Source: USDA, ARS, Midwest Area Office submitted to
FACTORS CONTRIBUTING TO PERSISTENCE OF HERBICIDES AND STRATEGIES FOR REDUCING OFF-TARGET IMPACTS
Sponsoring Institution
Agricultural Research Service/USDA
Project Status
TERMINATED
Funding Source
Reporting Frequency
Annual
Accession No.
0404405
Grant No.
(N/A)
Project No.
3611-12220-006-00D
Proposal No.
(N/A)
Multistate No.
(N/A)
Program Code
(N/A)
Project Start Date
Apr 6, 2001
Project End Date
Apr 5, 2006
Grant Year
(N/A)
Project Director
SIMS G K
Recipient Organization
USDA, ARS, Midwest Area Office
1201 W. Gregory Drive
Urbana,IL 61801
Performing Department
(N/A)
Non Technical Summary
(N/A)
Animal Health Component
30%
Research Effort Categories
Basic
70%
Applied
30%
Developmental
0%
Classification

Knowledge Area (KA)Subject of Investigation (SOI)Field of Science (FOS)Percent
1330110200020%
1331510206110%
1331820206110%
1332300206120%
1334010107010%
1335220100010%
2130110100020%
Goals / Objectives
1) Identify mechanisms of herbicide persistence associated with carryover damage and offsite movement. 2) Determine role of microbial inhibition in biodegradation of herbicides with anti-microbial properties. 3) Develop practical approaches to enhance degradation of xenobiotics used in agricultural production in order to limit onsite and offsite impacts. 4) Identify the major components of weed seeds accessed by microorganisms during seed decay, as well as factors that regulate seed decay.
Project Methods
Mechanisms of persistance will be investigated using a combination of soil incubation studies and cell permeability assays. Role of microbial inhibition will be evaluated using ALS-inhibiting herbicides and herbicides commonly partnered with these compounds. Field and laboratory studies will be involved. Objective 3 will be investigated using anaerobic conditions to promote degradation of trifluralin. The final objective will be addressed using isotopically labeled seeds to investigate microbial degradation of seed components.

Progress 04/06/01 to 04/05/06

Outputs
Progress Report 1. What major problem or issue is being resolved and how are you resolving it (summarize project aims and objectives)? How serious is the problem? Why does it matter? Weed management is one of the most critical components of successful crop production. At present, herbicides are the predominant tools for weed control in major crops in the United States. Widespread occurrence of agricultural chemicals in natural waters has stimulated interest in reducing or replacing the role of herbicides in agricultural management programs. Since effective alternatives to herbicides are not routinely available for use in most major crops, it is essential that present weed management practices be adapted in order to minimize the input of and offsite movement of herbicides. Herbicides vary widely in physical, chemical, and biological properties, as well as the manner in which they are used. These differences in properties result in variability in persistence (failure to decompose in the environment) and movement of herbicides away from the use area. Present approaches for evaluating environmental fate of pesticides focus on individual fate mechanisms, and usually ignore interactions among processes (coupled processes). This CRIS unit is involved in the evaluation of interacting fate processes and characterization of the factors controlling these processes for individual herbicides and closely related groups of herbicides. If we understand how the processes are coupled, and how these systems of coupled processes respond to environmental conditions, we can construct models that describe the complex and often unpredictable behavior of herbicides in the environment. The CRIS also examines fundamental processes in biologically based approaches for weed control and remediation of herbicide contamination. The research addresses the goals of National Programs 202 Soil Quality Management and 201, Water Quality Management. Specifically, each of the above objectives contributes to one or more components of the National Program 202 Action Plan. Key components addressed by this research include: Soil Conservation and Restoration Component, Problem Area 3: Remediation and Restoration (Improve knowledge of soil degradation and contamination processes and sources to prevent problems with soil fertility, environmental hazards, and food safety; Soil Biology Component, Problem Area 3: Interaction between soil management and soil biota (Determine short- and long-term effects of agricultural management practices on soil biological community populations, biodiversity, functioning, and resilience; and improve understanding of the specific roles of soil biota in interactions with soil chemical and physical processes to maximize efficient use of soil biota for crop growth; minimize the impact of management systems on the environment); Problem Area 5: Soil processes affecting transformation of pesticides and other xenobiotics (Develop knowledge and techniques that will minimize the impact of agrichemicals and other xenobiotics in the environment; Develop approaches to promote the degradation of xenobiotics in soils; Develop improved methods and decision aids for soils that require remediation to improve soil productivity, protect human health, and prevent environmental degradation). 2. List by year the currently approved milestones (indicators of research progress) Objective 1 (Persistence Mechanisms): 12 months-initiate N-heterocycle studies, recruit GRA for uptake work; 24 months-complete N-heterocycle work, publish, initiate uptake work; 36 months-complete uptake work, publish, recruit for mosture work; 48 months-initiate moisture studies; 60 months-complete moisture studies, publish results. Objective 2 (Bacterial resistance to ALS inhibitors): 12 months- establish field sites, monitor degradation, initiate isolations; 24 months-continue isolations, characterize isolates, publish; 36 months- characterize isolates, develop gene probes; 48 months-apply molecular probe techniques. Objective 3 (Remediation): 12 months-continue phyto-remediation project in progress; 24 months-complete phyto-remediation work/publish Recruit for dinitroaniline work; 36-months-initiate dinitroaniline prlject; 48 months-transfer phyto-remediation technology to users; 60 months-complete dinitroaniline project, transfer remediation technology to users. 4a List the single most significant research accomplishment during FY 2006. Problem Area 5 (soil processes affecting transformation of pesticides and other xenobiotics) of the USDA-ARS National Program 202 action plan, calls for developing knowledge and techniques that will minimize the impact of agrichemicals and other xenobiotics in the environment. Many of the processes affecting the behavior of herbicides in the environment are mediated by microorganisms, however little is known as to how environmental conditions or management practices regulate herbicide fate at the organism level. The majority of the research on this topic has depended on studies performed in culture or has examined community ecology without direct evidence that the organisms detected are actually involved in processes of interest. For FY 2006, applied DNA-based stable isotope probing to demonstrate the growth in soil of a native organism in response to the presence of the herbicide, 2,4-D. This was accomplished by introducing herbicide that had been labeled with a heavy isotope of carbon (13C) and separating heavy DNA formed when organisms in the soil grew on the labeled herbicide. This separated DNA was subjected to terminal restriction fragment length polymorphism (T-RFLP) to demonstrate the identity as well as the growth (increase in population) of native soil organisms metabolizing the herbicide. This work has provided the first such examination of native organisms actively degrading 2,4-D in soil without the need for isolation, and sets the stage for experiments that rigorously examine the effects of soil conditions and management practices on the dynamics of organisms involved in herbicide fate. 4b List other significant research accomplishment(s), if any. Problem Area 3 (interaction between soil management and soil biota) of the USDA-ARS National Program 202 action plan, is directed at determining short- and long-term effects of agricultural management practices on soil biological community populations, biodiversity, functioning, and resilience. Used soils from a long-term (greater than 100 years) fertility experiment to demonstrate the regulation of microbial degradation of the herbicides atrazine and cloransulam-methyl by soil nitrogen levels. The results indicate that fertility levels required for crop production are not conducive to degradation of these herbicides, which apparently undergo optimal degradation when the microbial community is starved for nitrogen. In collaboration with University of Illinois and US Army Corps of Engineers, we determined that an anaerobic organism known to degrade the explosive compound, RDX, was also able to transform a herbicide (trifluralin) that was structurally similar to the explosive. These results indicate that some of the progress made on treating sites contaminated with explosives may provide insight into the environmental behavior of certain herbicides called dinitroanilines, which are not explosive, but contain some of the same chemical structures found in RDX and TNT. 5. Describe the major accomplishments to date and their predicted or actual impact. In prior years, laboratory studies demonstrated the use of the herbicide atrazine as a nitrogen source by soil microorganisms, and that microbial degradation of atrazine may be in part prevented by the presence of nitrogen fertilizers in some organisms and in soil(addresses USDA-ARS National Program 202 Action Plan, Problem Area 5). Thus, one should consider the role of atrazine as a microbial N source when predicting the compounds fate in the environment. Studies with trifluralin strongly implicated a role of microbially modified iron minerals in the anaerobic (absence of oxygen) fate of this herbicide, and may account for rapid deactivation of this and other dinitroaniline herbicides in wet soils and sediments (addresses USDA-ARS National Program 202 Action Plan, Problem Area 3). Experiments were performed to examine the factors controlling degradation of pesticides and other organic compounds in soil. Degradation, sorption, and volatilization processes were apparently coupled in soil. Volatilization of the herbicide clomazone increased when degradation was eliminated by sterilization. Clomazone in soil water was preferentially utilized by microorganisms first, followed by slow release of clomazone from the solid phase to replace that lost from solution Addresses USDA-ARS National Program 202 Action Plan, Problem Area 3). During the course of conducting experiments on pesticide degradation, it became necessary to develop or adapt new methodology. For example, we developed a procedure for labeling nitrogen in the atrazine ring with a stable isotope, and discovered new chemistry for measurement of ammonium in soil and water. Such advances are important to research in other laboratories as well as our own. Studies were conducted on a newly registered herbicide, cloransulam- methyl, which has similar degradation properties across a wide range of soil types and conditions (addresses USDA-ARS National Program 202 Action Plan, Problem Area 3). The herbicide exhibited a pattern of temperature dependence similar to that observed in previous years with the herbicide clomazone. Degradation of the compound exhibited little dependence on soil moisture content, and the compound appeared to undergo significant non-biological degradation. The results of these studies will help identify proper seasonal windows for use of this compound with minimal negative environmental consequences. We examined sorption and degradation of the herbicide, isoxaflutole in soils of various organic matter content (addresses USDA-ARS National Program 202 Action Plan, Problem Area 3). Results showed that the herbicide is rapidly transformed to the herbicidally active product, diketonitrile. The parent herbicide remains sorbed to soil under dry conditions, and is rapidly degraded to release the diketonitrile when the soil is rewetted. These findings help explain the unusual rechargeable activity of this herbicide, in which the herbicide appears to be reactivated by rainfall immediately following dry periods. The ability of the aquatic plant, hornwort to remove herbicides from water was examined over a range of light and nutritional conditions. Both the plant and microorganisms living on the plants surfaces appeared to contribute to this process. These observations suggest that aquatic plants offer a promising alternative for remediation of pesticide contamination in waterways (addresses USDA-ARS National Program 202 Action Plan, Problem Area 5). Factors that limit availability of herbicides to microorganisms, such as soil sorption, or cellular uptake barriers, may contribute to herbicide persistence. The effects of ionization (formation of a charged molecule) of herbicides and model pollutants on uptake of the compounds by numerous species of bacteria was examined in pure culture using a range of pH conditions expected in the environment (addresses USDA-ARS National Program 202 Action Plan, Problem Area 3). As indicated by our previous findings, bacteria preferentially take up herbicides in their unionized (neutral) forms, and when these observations were then compared with the effects of ionization on adsorption of these compounds by soil solids, the results indicated that pH may have profound effects on both persistence and mobility of some herbicides in the environment. These findings are important to understanding variability in microbiological degradation of herbicides in the environment. Inhibition of soil microorganisms by herbicides has been reported sporadically in the literature, though mechanisms of inhibition and development of microbial resistance to herbicides have seldom been addressed in such studies. We examined the ecology of nitrification and herbicide biodegradation in the presence of mixtures of herbicides containing one or more components with anti-microbial properties (addresses USDA-ARS National Program 202 Action Plan, Problem Area 5). The results showed that, for some bacteria possessing enzymes sensitive to a particular herbicide, whole cells were insensitive due to permeability barriers, and in the field, we observed evidence for development of resistance of soil bacteria to certain inhibitory herbicides over time. These findings demonstrate the possibility of microbial adaptation to the presence of herbicides within a single growing season, thus providing an explanation for non-recurring persistence of some herbicides when first added as a component of a mixture, and may lead to management strategies for limiting herbicide carryover damage to crops in rotations. Environmental and toxicological characterization of herbicides is performed prior to any approved environmental release, though for practical and economic reasons, such information is too limited to predict behavior in all possible environmental situations. It is thus necessary to conduct additional studies on recently introduced compounds not only in anticipation of potential problems, but also to facilitate optimal use practices through a better understanding of behavior of the compound in the environment. Isoxaflutole is a recently registered herbicide representing a small class with a novel mode of action. The herbicide has some unusual features, including a highly reactive parent compound that is rapidly converted to an active herbicide product. Fundamental chemical properties, such as solubility and affinity for soil of the parent compound and the active form are quite different, leading to some difficulty in predicting both environmental and herbicidal behavior. Using advances made previously in the study of the soil sorption of this compound, we conducted studies that characterized the complex behavior of the compound in soil systems (addresses USDA-ARS National Program 202 Action Plan, Problem Area 3). The results explained one of the most unusual properties of the herbicide, the tendency to exhibit resurgent activity following precipitation. This behavior was found to be due to protection of the parent compound from activation, degradation, and leaching in dry soil owing to soil sorption. Upon rewetting, the parent compound is released from the soil surface and activated by exposure to the soil solution. The findings also showed the nature of the environmental behavior of the active product and a key, inactive degradation product. These findings will provide a better framework for the use of isoxaflutole, and may allow users to take advantage of the unusual behavior of the compound while guarding against potential negative environmental effects. Since the most significant impact of water regime on soil microorganisms in the North Central Region is the potential for anoxic conditions. Research on herbicide persistence under CRIS Objective 1 was focused on anaerobic herbicide degradation under flooded soil conditions (addresses USDA-ARS National Program 202 Action Plan, Problem Area 3). Initial findings of this work were reported last FY. For this FY, of the Invasive Weed Management Unit, in cooperation with University of Illinois, examined reductive dehalogenation (an important mechanism for detoxifying organic compounds in anoxic environments) of the herbicides, bromoxynil (3,5-dibromo-4-hydroxybenzonitrile) and ioxynil (3,5-diiodo-4- hydroxybenzonitrile), as well as the bromoxynil degradation product (3,5- dibromo-4-hydroxybenzoate) by the bacterium, Desulfitobacterium chlororespirans. We determined that cultures of D. chlororespirans not only actively removed bromine groups from bromoxynil and its soil metabolite, but appeared to use the process to support the organisms growth, while the other herbicide, ioxynil was only transformed when an additional electron acceptor was present, indicating that it could not be utilized as an electron acceptor for growth. To date, relatively few studies have examined reductive dehalogenation of herbicides, and this is the first report that carefully examines growth of an organism based on reductive debromination of a herbicide, as well as the only study demonstrating reductive removal of an iodine atom from a herbicide by a known organism, the impact of which is the likely occurrence of previously unexpected anaerobic biological transformations and resulting degradation products in the environment as a result of transient soil flooding. Many important microbial processes involving agricultural chemicals are dependent on the balance of carbon and nitrogen in the soil environment, however methods for examining the utilization of such chemicals as sources of either carbon or nitrogen are quite limited. In collaboration with University of Illinois scientists, we developed a method that allowed for quantitative recovery of both carbon and nitrogen incorporated into proteins by soil microorganisms (addresses USDA-ARS National Program 202 Action Plan, Problem Area 5). The method proved extremely successful on the model compound urea (a fertilizer that represents one of the simplest sources of both carbon and nitrogen for different groups of soil organisms), and was used to prove that nitrifying bacteria, previously known to utilize urea as a nitrogen and energy source, also utilize the compound as a source of carbon. The method will be invaluable for scientists studying the complex interactions of soil fertility and herbicide fate, and the findings with urea, which are the first to clearly demonstrate use of urea carbon by nitrifying bacteria, help explain why urea is among the most problematic nitrogen fertilizers with respect to nitrate pollution. Methods to identify organisms responsible for herbicide degradation have usually involved experimental conditions that differ significantly from those found in the environment. To investigate organisms responsible for in situ herbicide degradation, researchers from the Invasive Weed Management Unit, and a UIUC graduate student, developed a novel method, called 15N-DNA SIP, for identifying organisms capable of assimilating nitrogen containing compounds (addresses USDA-ARS National Program 202 Action Plan, Problem Area 3). The feasibility and limitations of the method were investigated by quantifying the separation of light and heavy (DNA that has incorporated the label) from two pure cultures (Escherichia coli and Micrococcus luteus) following 15N enrichment using the simple substrate 15NH4Cl. Also, using E. coli as a model organism, we investigated for the first time the effect of dual labels (15N and 13C) on the separation of light and heavy DNA. Additionally, we examined the effectiveness of separation of mixed DNA (14N and 15N DNA from E. coli and M. luteus) using terminal restriction fragment length polymorphism (T- RFLP) and quantitative real-time PCR. In summary, we developed a viable method for 15N DNA SIP that can now be applied to herbicides and environmental samples to better understand in situ processes. In collaboration with University of Illinois scientists, we determined that ammonia oxidizing bacteria (AOB) are able to utilize the N fertilizer, urea, as a source of carbon (addresses USDA-ARS National Program 202 Action Plan, Problem Area 3). AOB are of concern as they are largely responsible for the formation of nitrite and nitrate (common water contaminants)from N fertilizers. It has been previously suggested that urea provides an advantage to AOB in acidic soils, because urea is taken up more readily than ammonium when soils are acid. Our findings verified this theory, and also demonstrated that these organisms assimilate the carbon in the urea under a wide range of pH conditions, which may explain why urea is a better substrate than ammonia for AOB in soil, even though the organisms must first convert the urea to ammonium inside the cells. These observations may help explain why urea is among the most problematic nitrogen fertilizers with respect to nitrate pollution. 6. What science and/or technologies have been transferred and to whom? When is the science and/or technology likely to become available to the end- user (industry, farmer, other scientists)? What are the constraints, if known, to the adoption and durability of the technology products? Owing to the basic nature of much of the research, initial users are expected to be mostly scientists. Evidence for incorporation of the findings in approaches taken by the scientific community can be taken from an exponential increase in citations of products of this work in Science Citation Index over the life of the CRIS, as well as follow up research projects by other scientists in the areas of use of atrazine as an N source, and reduction of nitroaniline herbicides by reduced soil iron species. Agricultural industry consumers are made aware of the work through presentation of research findings and attendance of unit representatives at the University of Illinois Open House, Agronomy Day, and other field days, held each year. Our interactive approach to designing and conducting research allows us to share plans and results with other scientists from ARS, universities, and industry. These discussions guide our research, and provide insight to both public and private sector scientists seeking solutions to carryover injury and water contamination problems. Most of the other research results for this CRIS will likely undergo further development by applied scientists prior to adoption by producers. The results obtained in FY 2006 are expected to impact strategies for herbicide use over the next 5 years. 7. List your most important publications in the popular press and presentations to organizations and articles written about your work. (NOTE: List your peer reviewed publications below). Suszkiw, J. 2006. Unearthing new clues to controlling weeds. Agricultural Research, May, 2006. p. 20-21. Levy Larson. 2005. Research discovers fate of herbicides (press release). Available at http://www.aces.uiuc.edu/news/stories/news3270. html.

Impacts
(N/A)

Publications

  • Sims, G.K. 2006. Nitrogen starvation promotes biodegradation of n- heterocyclic compounds in soil. Soil Biology and Biochemistry, Vol 38. Available: http//www.sciencedirect.com.
  • Sims, G.K. 2006. Using the berthelot method for nitrite and nitrate analysis. Soil Science Society of America Journal. 70(3):1038.
  • Sims, G.K. 2006. Soil degradation. McGraw Hill Encyclopedia of Science and Technology, 10th ed. McGraw Hill, New York. Volume 16. Available: http://www.accesscience.com.
  • Sims, G.K., Holt, J.F. 2006. Anaerobic degradation of trifluralin [abstract]. Society of Environmental Toxicology and Chemistry, Platform Presentation No. CUP-1117-835394.
  • Cupples, A.M., Sims, G.K. 2006. Identification of 2,4-D degrading soil microorganisms with stable isotope probing [abstract]. American Society for Microbiology. 241/Q.
  • Sims, G.K., Shaffer, E.A., Cupples, A.M., Chee Sanford, J.C. 2006. Examining the ecology of heterocyclic N utilization [abstract]. International Society for Microbial Ecology Paper. 2668.


Progress 10/01/04 to 09/30/05

Outputs
1. What major problem or issue is being resolved and how are you resolving it (summarize project aims and objectives)? How serious is the problem? What does it matter? Weed management is one of the most critical components of successful crop production. At present, herbicides are the predominant tools for weed control in major crops in the United States. Widespread occurrence of agricultural chemicals in natural waters has stimulated interest in reducing or replacing the role of herbicides in agricultural management programs. Since effective alternatives to herbicides are not routinely available for use in most major crops, it is essential that present weed management practices be adapted in order to minimize the input of and offsite movement of herbicides. Herbicides vary widely in physical, chemical, and biological properties, as well as the manner in which they are used. These differences in properties result in variability in persistence (failure to decompose in the environment) and movement of herbicides away from the use area. Present approaches for evaluating environmental fate of pesticides focus on individual fate mechanisms, and usually ignore interactions among processes (coupled processes). This CRIS unit is involved in the evaluation of interacting fate processes and characterization of the factors controlling these processes for individual herbicides and closely related groups of herbicides. If we understand how the processes are coupled, and how these systems of coupled processes respond to environmental conditions, we can construct models that describe the complex and often unpredictable behavior of herbicides in the environment. The CRIS also examines fundamental processes in biologically based approaches for weed control and remediation of herbicide contamination. The research addresses the goals of National Programs 202 Soil Quality Management and 201, Water Quality Management. Specifically, each of the above objectives contributes to one or more components of the NP 202 Action Plan. Key components addressed include: Soil Conservation and Restoration Component, Problem Area 3: Remediation and Restoration (Improve knowledge of soil degradation and contamination processes and sources to prevent problems with soil fertility, environmental hazards, and food safety; Soil Biology Component, Problem Area 3: Interaction between soil management and soil biota (Determine short- and long-term effects of agricultural management practices on soil biological community populations, biodiversity, functioning, and resilience; and improve understanding of the specific roles of soil biota in interactions with soil chemical and physical processes to maximize efficient use of soil biota for crop growth; minimize the impact of management systems on the environment); Problem Area 5: Soil processes affecting transformation of pesticides and other xenobiotics (Develop knowledge and techniques that will minimize the impact of agrichemicals and other xenobiotics in the environment; Develop approaches to promote the degradation of xenobiotics in soils; Develop improved methods and decision aids for soils that require remediation to improve soil productivity, protect human health, and prevent environmental degradation). 2. List the milestones (indicators of progress) from your Project Plan. Objective 1 (Persistence Mechanisms): 12 months-initiate N-heterocycle studies, recruit GRA for uptake work; 24 months-complete N-heterocycle work, publish, initiate uptake work; 36 months-complete uptake work, publish, recruit for moisture work; 48 months-initiate moisture studies; 60 months-complete moisture studies, publish results. Objective 2 (Bacterial resistance to ALS inhibitors): 12 months- establish field sites, monitor degradation, initiate isolations; 24 months-continue isolations, characterize isolates, publish; 36 months- characterize isolates, develop gene probes; 48 months-apply molecular probe techniques. Objective 3 (Remediation): 12 months- continue phyto-remediation project in progress; 24 months- complete phyto-remediation work/publish Recruit for dinitroaniline work; 36-months-initiate dinitroaniline project; 48 months-transfer phyto-remediation technology to users; 60 months- complete dinitroaniline project, transfer remediation technology to users. Objective 4 (Weed seed decay ): 12 months- recruit personnel, conduct preliminary studies; 24 months- initiate spectro-scopic studies/ labeling studies; 36 months- continue spectroscopic work, label plants; 48 months- characterize labeled materials, publish results; 60 months- participate in follow-up studies with collaborators. 3a List the milestones that were scheduled to be addressed in FY 2005. For each milestone, indicate the status: fully met, substantially met, or not met. If not met, why. 1. Persistence mechanisms: Initiate moistue studies. Milestone Fully Met 2. Bacterial resistance to ALS inhibitors: Apply molecular probe techniques. Milestone Fully Met 3. Remediation: Complete dinitroaniline project. Milestone Substantially Met 4. Weed seed decay: Characterize labeled materials and publish results. Milestone Substantially Met 3b List the milestones that you expect to address over the next 3 years (FY 2006, 2007, and 2008). What do you expect to accomplish, year by year, over the next 3 years under each milestone? The milestones to be addressed over the next three years are defined only through April 2006, since this is the project termination date. New milestones are under development and a project plan will be submitted according to the schedule set forth by NPS. Milestones for FY 06 (60 month) are as follows: Objective 1: Complete moisture studies, publish results. Objective 3: Transfer remediation technology to users. Objective 4: Participate in follow-up studies with collaborators. For the first objective, this will consist largely of additional studies on anaerobic degradation in soils, as well as examining the role of carbon and nitrogen balance on degradation of herbicides, especially those containing nitrogen, utilizing the stable isotope method developed this year. For objective three (remediation), we intend to complete our tests on the effectiveness of the remediation approach developed for trifluralin, and, if fully successful, make this information available through our ARS web site, and distribution to contacts in regulatory agencies and environmental consulting firms. For objective 4, we will continue to identify and examine specific soil- related factors that influence microbial-mediated seed decay of velvetleaf and giant ragweed. A shift in approach due to the discovery of a wide range of water-soluble chemical exudates produced by seeds will preclude the use of isotopically labeled seed biomarkers for evaluating the fate of seeds in soil environments. The focus of study with seed exudates will be to examine their significance in microbial seed decay processes. These studies will be conducted in conjunction with the main objectives in CRIS project 3611-22000-018-00D in our unit. 4a What was the single most significant accomplishment this past year? To date, all methods to identify organisms responsible for herbicide degradation involve experimental conditions that differ significantly from those found in the environment in situ. To investigate organisms responsible for herbicide degradation, researchers Alison Cupples, Gerald Sims, Joanne Chee-Sanford from the Invasive Weed Management Unit, and Beth Shaffer, a UIUC graduate student, developed a novel method, called 15N-DNA SIP, for identifying organisms capable of assimilating nitrogen containing compounds. The feasibility and limitations of the method were investigated by quantifying the separation of light and heavy (DNA that has incorporated the label) from two pure cultures (Escherichia coli and Micrococcus luteus) after the bacteria had been fed a labeled nitrogen source. Also, using E. coli as a model organism, we investigated for the first time the effect of dual labels (nitrogen and carbon) on the separation of light and heavy DNA. Additionally, we examined the effectiveness of separation of mixed DNA (labeled and unlabeled DNA from E. coli and M. luteus) using molecular biology techniques called terminal restriction fragment length polymorphism (T-RFLP) and quantitative real- time PCR. In summary, we developed a viable method for 15N DNA SIP that can now be applied to herbicides and environmental samples to better understand in situ processes. 4b List other significant accomplishments, if any. In collaboration with University of Illinois scientists, Dr. Richard Mulvaney and Kerri Marsh, we determined that ammonia oxidizing bacteria (AOB) are able to utilize the N fertilizer, urea, as a source of carbon. AOB are of concern as they are largely responsible for the formation of nitrite and nitrate (common water contaminants)from N fertilizers. It has been previously suggested that urea provides an advantage to AOB in acidic soils, because urea is taken up more readily than ammonium when soils are acid. Our findings verified this theory, and also demonstrated that these organisms assimilate the carbon in the urea under a wide range of pH conditions, which may explain why urea is a better substrate than ammonia for AOB in soil, even though the organisms must first convert the urea to ammonium inside the cells. These observations may help explain why urea is among the most problematic nitrogen fertilizers with respect to nitrate pollution. 4d Progress report. Work under Obj. 1 scheduled for the 48 month milestone (bioavailability of herbicides as a function of moisture status) was addressed ahead of schedule in previous years, however, since the effect of moisture regime on soil oxygen status was not addressed, such work was initiated in FY 04. For FY 05, work initiated with Desulfitobacterium chlororespirans, to examine anaerobic degradation of the herbicides bromoxynil and ioxynil was completed and submitted for publication. The published paper is listed in this report. Research addressing the issues of bacterial sensitivity to ALS- inhibiting herbicides (Obj. 2) was reported in previous FYs. For FY 05, we worked on adapting a stable isotope probing technique for use in this project. This approach would facilitate separating DNA from ogranisms actively utilizing a herbicide from the bulk DNA of the microbial community, and thus allow us to expand the work on Obj. 2 beyond our original expectations. The approach was successful and has been developed as a methods paper and submitted for publication. We are presently applying the technique to determine whether partner herbicides affect the organisms responsible for degradation of a herbicide of interest in soil. In FY 04, we developed methods to verify the utilization of agricultural chemicals as either carbon or nitrogen sources for microbial growth in soils by ensuring the incorporation of labeled C or N derived from compound of interest into microbial cell proteins. In FY 05, this approach was applied successfully to the test compound, urea, and the findings were published. Prior year research under Obj. 3 (remediation mechanisms) suggested the need for greater knowledge of anaerobic biodegradation of herbicides. This topic was developed as a postdoctoral research associate proposal, and was funded. Two postdoctoral fellows, one supported by the CRIS and the other through the competitive postdoctoral program conducted research on anaerobic biodegradation of herbicides from the perspectives of persistence mechanisms (Obj. 1) and remediation tools (Obj. 3). Accomplishments are reported for both objectives. The 48 month milestone under Ojb. 4 addressed the subject of weed seed decay. Weed seed decay work is a primary focus of another CRIS (3611- 22000-018-00D; Biologically and ecologically-based knowledge for integrated weed management systems) in the management unit, and progress made in this area has been reported separately by Joanne Chee-Sanford under that project. Additional collaboration within the management unit related to the NP 304 mission, but not specifically detailed in the milestone plan was directed toward biocontrol of weeds (Amaranthus spp.) using the fungal organisms, Phomopsis amaranthicola, and Microsphaeropsis amaranthi. Early accomplishments for this work were reported in FY 04. This work was completed in FY 05, a manuscript was submitted for publication, and a presentation of the research findings made at a scientific meeting. Under conditions of carbon selection,where weed seeds provided the major sources of carbon nutrition, seeds of different species undergo a range of microbialmediated decay. With velvetleaf, in particular, regardless of different microbial communities derived from a variety of soil samples, decay of velvetleaf seeds is consistent and extensive. This result suggests that despite significant variations in microbial community assemblages on seeds when challenged with whole soil microbial communities, the same ecological niche associated with seed decay processes is filled by a wide variety of naturally-occurring, common soil bacteria. Furthermore, seeds of species such as velvetleaf can provide significant carbon nutrition for growth of native soil microorganisms, contributing to the overall bioavailable carbonreservior. This further suggests that the potential for seed decay of certain weed species is expected to be widely distributed in nature, however, because seeds are known to persist in soil for long periods of time, factors must be present that restrict seed decay in natural soil. Water-soluble exudates were found to be produced by seeds of a number of species of weeds, suggesting their possible role in mechanisms of protection, associations with other biota, soil chemical ecology, and possible intra- and interspecies plant relationships. Compounds from weeds seeds are emerging as natural products with ecological significance, and are being investigated as seed chemical constituents that may serve as biomarkers for investigating seed decay or seed constituents that may serve as biomarkers for investigating seed decay or seed fate. The discovery of these compounds has allowed a major shift in approach to examing seed fate in nature, facilitating studies to track seed fate without the use of complex chemical labeling of seeds. 5. Describe the major accomplishments over the life of the project, including their predicted or actual impact. In prior years, laboratory studies demonstrated the use of the herbicide atrazine as a nitrogen source by soil microorganisms, and that microbial degradation of atrazine may be in part prevented by the presence of nitrogen fertilizers in some organisms and in soil. Thus, one should consider the role of atrazine as a microbial N source when predicting the compounds fate in the environment. Studies with trifluralin strongly implicated a role of microbially modified iron minerals in the anaerobic (absence of oxygen) fate of this herbicide, and may account for rapid deactivation of this and other dinitroaniline herbicides in wet soils and sediments. Experiments were performed to examine the factors controlling degradation of pesticides and other organic compounds in soil. Degradation, sorption, and volatilization processes were apparently coupled in soil. Volatilization of the herbicide clomazone increased when degradation was eliminated by sterilization. Clomazone in soil water was preferentially utilized by microorganisms first, followed by slow release of clomazone from the solid phase to replace that lost from solution. During the course of conducting experiments on pesticide degradation, it became necessary to develop or adapt new methodology. For example, we developed a procedure for labeling nitrogen in the atrazine ring with a stable isotope, and discovered new chemistry for measurement of ammonium in soil and water. Such advances are important to research in other laboratories as well as our own. Studies were conducted on a newly registered herbicide, cloransulam- methyl, which has similar degradation properties across a wide range of soil types and conditions. The herbicide exhibited a pattern of temperature dependence similar to that observed in previous years with the herbicide clomazone. Degradation of the compound exhibited little dependence on soil moisture content, and the compound appeared to undergo significant non-biological degradation. The results of these studies will help identify proper seasonal windows for use of this compound with minimal negative environmental consequences. We examined sorption and degradation of the herbicide, isoxaflutole in soils of various organic matter content. Results showed that the herbicide is rapidly transformed to the herbicidally active product, diketonitrile. The parent herbicide remains sorbed to soil under dry conditions, and is rapidly degraded to release the diketonitrile when the soil is rewetted. These findings help explain the unusual rechargeable activity of this herbicide, in which the herbicide appears to be reactivated by rainfall immediately following dry periods. The ability of the aquatic plant, hornwort to remove herbicides from water was examined over a range of light and nutritional conditions. Both the plant and microorganisms living on the plants surfaces appeared to contribute to this process. These observations suggest that aquatic plants offer a promising alternative for remediation of pesticide contamination in waterways. Factors that limit availability of herbicides to microorganisms, such as soil sorption, or cellular uptake barriers, may contribute to herbicide persistence. The effects of ionization (formation of a charged molecule) of herbicides and model pollutants on uptake of the compounds by numerous species of bacteria was examined in pure culture using a range of pH conditions expected in the environment. As indicated by our previous findings, bacteria preferentially take up herbicides in their unionized (neutral) forms, and when these observations were then compared with the effects of ionization on adsorption of these compounds by soil solids, the results indicated that pH may have profound effects on both persistence and mobility of some herbicides in the environment. These findings are important to understanding variability in microbiological degradation of herbicides in the environment. Inhibition of soil microorganisms by herbicides has been reported sporadically in the literature, though mechanisms of inhibition and development of microbial resistance to herbicides have seldom been addressed in such studies. We examined the ecology of nitrification and herbicide biodegradation in the presence of mixtures of herbicides containing one or more components with anti-microbial properties. The results showed that, for some bacteria possessing enzymes sensitive to a particular herbicide, whole cells were insensitive due to permeability barriers, and in the field, we observed evidence for development of resistance of soil bacteria to certain inhibitory herbicides over time. These findings demonstrate the possibility of microbial adaptation to the presence of herbicides within a single growing season, thus providing an explanation for non-recurring persistence of some herbicides when first added as a component of a mixture, and may lead to management strategies for limiting herbicide carryover damage to crops in rotations. Environmental and toxicological characterization of herbicides is performed prior to any approved environmental release, though for practical and economic reasons, such information is too limited to predict behavior in all possible environmental situations. It is thus necessary to conduct additional studies on recently introduced compounds not only in anticipation of potential problems, but also to facilitate optimal use practices through a better understanding of behavior of the compound in the environment. Isoxaflutole is a recently registered herbicide representing a small class with a novel mode of action. The herbicide has some unusual features, including a highly reactive parent compound that is rapidly converted to an active herbicide product. Fundamental chemical properties, such as solubility and affinity for soil of the parent compound and the active form are quite different, leading to some difficulty in predicting both environmental and herbicidal behavior. Using advances made previously in the study of the soil sorption of this compound, we conducted studies that characterized the complex behavior of the compound in soil systems. The results explained one of the most unusual properties of the herbicide, the tendency to exhibit resurgent activity following precipitation. This behavior was found to be due to protection of the parent compound from activation, degradation, and leaching in dry soil owing to soil sorption. Upon rewetting, the parent compound is released from the soil surface and activated by exposure to the soil solution. The findings also showed the nature of the environmental behavior of the active product and a key, inactive degradation product. These findings will provide a better framework for the use of isoxaflutole, and may allow users to take advantage of the unusual behavior of the compound while guarding against potential negative environmental effects. Since the most significant impact of water regime on soil microorganisms in the North Central Region is the potential for anoxic conditions. Research on herbicide persistence under CRIS Objective 1 was focused on anaerobic herbicide degradation under flooded soil conditions. Initial findings of this work were reported last FY. For this FY, Research Associate, Dr. Alison Cupples of the Invasive Weed Management Unit, in cooperation with Dr. Robert Sanford, University of Illinois, examined reductive dehalogenation (an important mechanism for detoxifying organic compounds in anoxic environments) of the herbicides, bromoxynil (3,5- dibromo-4-hydroxybenzonitrile) and ioxynil (3,5-diiodo-4- hydroxybenzonitrile), as well as the bromoxynil degradation product (3,5- dibromo-4-hydroxybenzoate) by the bacterium, Desulfitobacterium chlororespirans. We determined that cultures of D. chlororespirans not only actively removed bromine groups from bromoxynil and its soil metabolite, but appeared to use the process to support the organisms growth, while the other herbicide, ioxynil was only transformed when an additional electron acceptor was present, indicating that it could not be utilized as an electron acceptor for growth. To date, relatively few studies have examined reductive dehalogenation of herbicides, and this is the first report that carefully examines growth of an organism based on reductive debromination of a herbicide, as well as the only study demonstrating reductive removal of an iodine atom from a herbicide by a known organism, the impact of which is the likely occurrence of previously unexpected anaerobic biological transformations and resulting degradation products in the environment as a result of transient soil flooding. Recent research showing rapid decomposition of trifluralin in saturated soils was confirmed by other scientists with other nitro-aromatic herbicides, suggesting the potential of soil flooding to remedy contamination by this family of herbicides, and the possibility of using soil iron reduction to predict dinitroaniline herbicide performance failures in saturated soils. We conducted studies to identify parameters that would allow prediction of conditions conducive to reduction of iron in temporarily saturated surface soils, using surface soil samples representing the major soil orders. In order to examine the potential for the fungal herbicides, Microsphaeropsis amaranthi and Phomopsis amaranthicola to control Amaranthus spp. common to Illinois, host plant susceptibility studies were conducted on A. rudis, A. tuberculatus, A. retroflexus, A. hybridus, A. powellii, A. spinosus, A. albus, A. blitoides, and A. palmeri. Dew chamber and greenhouse studies were initiated to evaluate conditions that favor rapid development of the fungi. Many important microbial processes involving agricultural chemicals are dependent on the balance of carbon and nitrogen in the soil environment, however methods for examining the utilization of such chemicals as sources of either carbon or nitrogen are quite limited. In collaboration with University of Illinois scientists Dr. Richard Mulvaney and Kerri Marsh, we developed a method that allowed for quantitative recovery of both carbon and nitrogen incorporated into proteins by soil microorganisms. The method proved extremely successful on the model compound urea (a fertilizer that represents one of the simplest sources of both carbon and nitrogen for different groups of soil organisms), and was used to prove that nitrifying bacteria, previously known to utilize urea as a nitrogen and energy source, also utilize the compound as a source of carbon. The method will be invaluable for scientists studying the complex interactions of soil fertility and herbicide fate, and the findings with urea, which are the first to clearly demonstrate use of urea carbon by nitrifying bacteria, help explain why urea is among the most problematic nitrogen fertilizers with respect to nitrate pollution. 6. What science and/or technologies have been transferred and to whom? When is the science and/or technology likely to become available to the end- user (industry, farmer, other scientists)? What are the constraints, if known, to the adoption and durability of the technology products? Owing to the basic nature of much of the research, initial users are expected to be mostly scientists. Evidence for incorporation of the findings in approaches taken by the scientific community can be taken from an exponential increase in citations of products of this work in Science Citation Index over the life of the CRIS, as well as follow up research projects by other scientists in the areas of use of atrazine as an N source, and reduction of nitro-aniline herbicides by reduced soil iron species. Agricultural industry consumers are made aware of the work through presentation of research findings and attendance of unit representatives at field days, held each year. Our interactive approach to designing and conducting research allows us to share plans and results with other scientists from ARS, universities, and industry. These discussions guide our research, and provide insight to both public and private sector scientists seeking solutions to carryover injury and water contamination problems. Most of the other research results for this CRIS will likely undergo further development by applied scientists prior to adoption by producers. The results obtained in FY 2005 are expected to impact strategies for herbicide use over the next 5 years.

Impacts
(N/A)

Publications

  • Marsh, K.L., Sims, G.K., Mulvaney, R.L. 2005. Availability of urea to autotriphic ammonia-oxidizing bacteria as related to the fate of 145c- and 15N-labeled urea added to soil. Biol Fertil Soils. 102(1):DOI:10. 1007/s00374-005-0004-2.
  • Cupples, A.M., Sanford, R.A, Sims, G.K. 2005. Dehalogenation of the herbicides bromoxynil (3,5-dibromo-4-hydroxybenzonitrile) and loxynil (3,5- diiodino-4-hydroxybenzonitrile) by desulfitobacterium chlororespirans [abstract]. American Society for Microbiology, 105th General Meeting. No. Q-015.
  • Sims, G.K., Chee Sanford, J.C., Cupples, A.M., Shaffer, E.A. 2005. Nutritional limitations for biodegradation of herbicides [abstract]. Weed Science Society of America. 44:74.
  • Ortiz-Ribbing, L.M., Williams, M.M. 2005. Two fungal organisms, phomopsis amaranthicola and microsphaeropsis amaranthi, infect several weedy amaranthus species [abstract]. Weed Science Society of America Meeting. 45:63.
  • Cupples, A.M., Sanford, R.A., Sims, G.K. 2005. Dehalogenation of the herbicides bromoxynil (3,5-dibromo-4-hydroxybenzonitrile) and ioxynil (3,5- diiodino-4-hydroxybenzonitrile) by desulfitobacterium chlororespirans. Applied and Environmental Microbiology. 71(7):3741-3746.
  • Beasley, J.S., Branham, B.E., Ortiz Ribbing, L.M. 2005. Trinexapac-ethyl affects kentucky bluegrass (poa pratensis l.) root characteristics. Hortscience. 40(5):1539-1542.


Progress 10/01/03 to 09/30/04

Outputs
1. What major problem or issue is being resolved and how are you resolving it (summarize project aims and objectives)? How serious is the problem? What does it matter? Weed management is one of the most critical components of successful crop production. At present, herbicides are the predominant tools for weed control in major crops in the United States. Widespread occurrence of agricultural chemicals in natural waters has stimulated interest in reducing or replacing the role of herbicides in agricultural management programs. Since effective alternatives to herbicides are not routinely available for use in most major crops, it is essential that present weed management practices be adapted in order to minimize the input of and offsite movement of herbicides. Herbicides vary widely in physical, chemical, and biological properties, as well as the manner in which they are used. These differences in properties result in variability in persistence (failure to decompose in the environment) and movement of herbicides away from the use area. Present approaches for evaluating environmental fate of pesticides focus on individual fate mechanisms, and usually ignore interactions among processes (coupled processes). This CRIS is involved in the evaluation of interacting fate processes and characterization of the factors controlling these processes for individual herbicides and closely related groups of herbicides. If we understand how the processes are coupled, and how these systems of coupled processes respond to environmental conditions, we can construct models that describe the complex and often unpredictable behavior of herbicides in the environment. The CRIS also examines fundamental processes in biologically based approaches for weed control and remediation of herbicide contamination. The research addresses the goals of National Programs 202 Soil Quality Management and 201, Water Quality Management. Specifically, each of the above objectives contributes to one or more components of the National Program 202 Action Plan. Key components addressed by this research include: Soil Conservation and Restoration Component, Problem Area 3: Remediation and Restoration (Improve knowledge of soil degradation and contamination processes and sources to prevent problems with soil fertility, environmental hazards, and food safety; Soil Biology Component, Problem Area 3: Interaction between soil management and soil biota (Determine short- and long-term effects of agricultural management practices on soil biological community populations, biodiversity, functioning, and resilience; and improve understanding of the specific roles of soil biota in interactions with soil chemical and physical processes to maximize efficient use of soil biota for crop growth; minimize the impact of management systems on the environment); Problem Area 5: Soil processes affecting transformation of pesticides and other xenobiotics (Develop knowledge and techniques that will minimize the impact of agrichemicals and other xenobiotics in the environment; Develop approaches to promote the degradation of xenobiotics in soils; Develop improved methods and decision aids for soils that require remediation to improve soil productivity, protect human health, and prevent environmental degradation). 2. List the milestones (indicators of progress) from your Project Plan. Milestones for the CRIS project were developed to indicate progress for each of the four objectives at 12, 24, 36, 48, and 60 months in the project plan. The objectives include: (1) identifying mechanisms involved in sporadic occurrences of persistence of herbicides; (2) determining the role of microbial inhibition in the biodegradation of mixtures of herbicides containing one or more components with anti- microbial properties; (3) developing practical approaches to enhance degradation of xenobiotics used in agricultural production in order to limit off-target impacts of these compounds, and; (4) identifying the major components of weed seeds accessed by microorganisms during seed decay, as well as factors that regulate decay of these seeds. The milestones for these four objectives are as follows for FY 04 (48 month milestones): Objective 1 (persistence mechanisms): Initiate moisture studies. Objective 2 (bacterial resistance to ALS inhibitors): Apply molecular probe techniques. Objective 3 (remediation): Complete dinitroaniline project. Objective 4 (weed seed decay): Characterize labeled materials and publish results. Milestones for FY 05 (60 month) are as follows: Objective 1: Complete moisture studies, publish results. Objective 3: Transfer remediation technology to users. Objective 4: Participate in follow-up studies with collaborators. 3. Milestones: A. List the milestones that were scheduled to be addressed in FY 2004. How many milestones did you fully or substantially meet in FY 2004 and indicate which ones were not fully or substantially met, briefly explain why not, and your plans to do so. The milestones discussed below for FY 2004 correspond to Month 48 on the project plan schedule, and primarily address objectives 1, 3, and 4. Research addressing the issues of bacterial sensitivity to ALS-inhibiting herbicides (Objective 2) was completed in the previous FY. Work under Objective 1 scheduled for the 48 month milestone (bioavailability of herbicides as a function of moisture status) had also been addressed ahead of schedule in previous years, however since the effect of moisture regime on soil oxygen status was not addressed, this work was initiated in FY 04 and is discussed in this report. Prior year research under Objectives 1 and 3 (remediation mechanisms) suggested the need for greater knowledge of anaerobic biodegradation of herbicides. This topic was developed as a postdoctoral research associate proposal, and was funded. Two postdoctoral fellows, one supported by the CRIS and the other through the competitive postdoctoral program conducted research on anaerobic biodegradation of herbicides from the perspectives of persistence mechanisms (objective 1) and remediation tools (objective 3). The 48 month milestone under objective 4 addressed the subject of weed seed decay. Weed seed decay work is a primary focus of another CRIS (3611-22000-017-00D, Developing biological/ecological knowledge for enhancing weed management systems) in the management unit, and progress made in this area has been reported separately by Joanne Chee-Sanford under that project. Additional collaboration within the management unit related to the National Program 304 mission, but not specifically detailed in the milestone plan was directed toward biocontrol of weeds (Amaranthus spp.) using the fungal organisms, Phomopsis amaranthicola, and Microsphaeropsis amaranthi. The milestones listed below were met: Our recent research has shown that the rapid decomposition of trifluralin in saturated soils is restricted to iron-reducing soil conditions. This work has been confirmed by other scientists with other nitro-aromatic herbicides, suggesting the potential of soil flooding to remedy contamination by this family of herbicides, and the possibility of using soil iron reduction to predict dinitroaniline herbicide performance failures in saturated soils. This FY, we set out to identify parameters that will allow prediction of conditions conducive to reduction of iron in temporarily saturated surface soils. Sixty-three surface soil samples representing the major soil orders were collected through the collaborative efforts of scientists in 28 states. Soils were characterized as to soil texture, organic matter, soil pH, cation exchange capacity, available phosphorus, exchangeable potassium, magnesium, calcium, sulfur, zinc, manganese, iron, copper and boron concentrations. The soils were extracted using the Citrate- Dithioniate analyzed using Atomic Absorption Spectrometry to determine 'Free"-iron oxide concentrations, and studies initiated to simulate flooded soil conditions. Moisture studies under objective 1 (herbicide persistence mechanisms) focused on anaerobic herbicide degradation under flooded soil conditions. Using the organism, Desulfitobacterium chlororespirans, we examined anaerobic degradation of the herbicides bromoxynil and ioxynil. Pure culture techniques, liquid chromatography and gas chromatography-mass spectrometry were used to determine not only the degradation of the herbicides, but to identify the products formed and the mechanisms involved. In order to examine the potential for the fungal herbicides, Microsphaeropsis amaranthi and Phomopsis amaranthicola to control Amaranthus spp. common to Illinois, host plant susceptibility studies were conducted on A. rudis, A. tuberculatus, A. retroflexus, A. hybridus, A. powellii, A. spinosus, A. albus, A. blitoides, and A. palmeri. Dew chamber and greenhouse studies were initiated to evaluate conditions that favor rapid development of the fungi. Since previous findings showed that some herbicides, such as atrazine, may be better nitrogen than carbon sources for microorganisms, we developed methods to verify the utilization of these materials as either carbon or nitrogen sources for microbial growth in soils by measuring the incorporation of labeled C or N derived from a compound of interest into microbial cell proteins. B. List the milestones that you expect to address over the next 3 years (FY 2005, 2006, & 2007). What do you expect to accomplish, year by year, over the next 3 years under each milestone? The milestones to be addressed in FY 2005 are: FY 2005 represents the last full year of the project, which terminates in April, 2006. Milestones will be those listed at 60 months in the schedule above. For the first objective, this will consist largely of additional studies on anaerobic degradation in soils, as well as examining the role of carbon and nitrogen balance on degradation of herbicides containing nitrogen, utilizing the method developed this past year for urea. For objective three (remediation), we intend to test the effectiveness of the remediation approach developed for trifluralin, and compare the agreement of predictive parameters developed this FY on the rate and extent of soil iron reduction and herbicide degradation under flooded conditions. 4. What were the most significant accomplishments this past year? A. Single most significant accomplishment during FY2004: Since the most significant impact of water regime on soil microorganisms in the North Central Region is the potential for anoxic conditions, research on herbicide persistence under CRIS Objective 1 was focused on anaerobic herbicide degradation under flooded soil conditions. Research Associate, Dr. Alison Cupples of the Invasive Weed Management Unit, in cooperation with Dr. Robert Sanford, University of Illinois, examined reductive dehalogenation (an important mechanism for detoxifying organic compounds in anoxic environments) of the herbicides, bromoxynil (3,5- dibromo-4-hydroxybenzonitrile) and ioxynil (3,5-diiodo-4- hydroxybenzonitrile), as well as the bromoxynil degradation product (3,5- dibromo-4-hydroxybenzoate) by the bacterium, Desulfitobacterium chlororespirans. We determined that cultures of D. chlororespirans not only actively removed bromine groups from bromoxynil and its soil metabolite, but appeared to use the process to support the organism's growth, while the other herbicide, ioxynil was only transformed when an additional electron acceptor was present, indicating that it could not be utilized as an electron acceptor for growth. To date, relatively few studies have examined reductive dehalogenation of herbicides, and this is the first report that carefully examines growth of an organism based on reductive debromination of a herbicide, as well as the only study demonstrating reductive removal of an iodine atom from a herbicide by a known organism, the impact of which is the likely occurrence of previously unexpected anaerobic biological transformations and resulting degradation products in the environment as a result of transient soil flooding. B. Other significant accomplishment(s). Many important microbial processes involving agricultural chemicals are dependent on the balance of carbon and nitrogen in the soil environment, however methods for examining the utilization of such chemicals as sources of either carbon or nitrogen are quite limited. In collaboration with University of Illinois scientists Dr. Richard Mulvaney and Kerri Marsh, we developed a method that allowed for quantitative recovery of both carbon and nitrogen incorporated into proteins by soil microorganisms. The method proved extremely successful on the model compound urea (a fertilizer that represents one of the simplest sources of both carbon and nitrogen for different groups of soil organisms), and was used to prove that nitrifying bacteria, previously known to utilize urea as a nitrogen and energy source, also utilize the compound as a source of carbon. The method will be invaluable for scientists studying the complex interactions of soil fertility and herbicide fate, and the findings with urea, which are the first to clearly demonstrate use of urea carbon by nitrifying bacteria, help explain why urea is among the most problematic nitrogen fertilizers with respect to nitrate pollution. Many of the most important herbicides for weed control in soybean are nitro-aromatic compounds (e.g. trifluralin, pendimethalin, fomesafen), which are degraded rapidly by reduced iron minerals commonly occurring under saturated soil conditions, and result in frequent herbicide failures. Researchers, Dr. Loretta Ortiz-Ribbing and Dr. Gerald Sims of the Invasive Weed Management Unit, and collaborator Jon Holt, University of Illinois, are examining herbicide deactivation (iron-reduction) and its correlation to soil factors such as soil organic matter, soil texture, iron oxide concentrations and soil pH to determine whether it may provide information for a predictive model for growers. To date, we gave collected 63 soil samples through the collaborative efforts of 28 scientists in 25 states, characterized soils as to texture, organic matter, soil pH, cation exchange capacity, available phosphorus, exchangeable potassium, magnesium, calcium, and for sulfur, zinc, manganese, iron, copper and boron concentrations, as well as 'Free" -iron oxide concentrations, and initiated an experiment employing simulating flooded soil conditions. This research, which is among very few studies examining iron-reduction over a wide variety of soils, would allow managers to potentially predict the occurrence of conditions conducive to reduction of iron in temporarily saturated surface soils, thus facilitating decisions regarding remediation of nitro-aromatic herbicide spills and timing of soil applied herbicides in soybean production. Given that species of the Amaranthus genus are some of the most troublesome weeds in crop production, especially since several Amaranthus spp. have developed resistance to multiple herbicide families, research has focused identifing alternative control methods (biological control) of Amaranthus spp. Drs. Loretta Ortiz-Ribbing and Marty Williams, of the Invasive Weed Management Unit, are examining the role of two fungal pathogens (Microsphaeropsis amaranthi and Phomopsis amaranthicola) isolated from Amaranthus spp., to enhance weed control. We determined that for the eight Amaranthus spp. common to Illinois (A. rudis, A. tuberculatus, A. retroflexus, A. hybridus, A. powellii, A. spinosus, A. albus, A. blitoides, and A. palmeri), infection by M. amaranthi and P. amaranthicola appears to be favored by high dew periods after application, and though high relative humidity (90-100%) may provide some infection, surface leaf moisture appears to be more critical for infection and development of lesions on the stem of the weeds (lesions on the leaf do not appear to provide sufficient damage for plant death). Preliminary results indicate that Phomopsis amaranthicola may have a wider weed host range than Microsphaeropsis amaranthi, while a mixture of both pathogens provides a synergist effect. The impact of this research will allow the development of alternative weed control methods that would reduce the reliance on current herbicide use, thus reducing selection pressure for development of herbicide resistance. C. Significant Activities that Support Special Target Populations None D. Progress Report opportunity to submit additional programmatic information to your Area Office and NPS. When the CRIS project was developed in 2001, the Invasive Weed Management Unit had a completely different complement of scientists, with Sims, now Research Leader, the only SY remaining in the unit since the project plan was written. In September, 2004, the final SY position will be filled, and the group will carefully examine all of the objectives in the CRIS project for potential modifications that could benefit from the additional expertise present in the unit. All scientists will be involved in the development of the next project plan. 5. Describe the major accomplishments over the life of the project, including their predicted or actual impact. In prior years, laboratory studies demonstrated the use of the herbicide atrazine as a nitrogen source by soil microorganisms, and that microbial degradation of atrazine may be in part prevented by the presence of nitrogen fertilizers in some organisms and in soil. Thus, one should consider the role of atrazine as a microbial N source when predicting the compound's fate in the environment. Studies with trifluralin strongly implicated a role of microbially modified iron minerals in the anaerobic (absence of oxygen) fate of this herbicide, and may account for rapid deactivation of this and other dinitroaniline herbicides in wet soils and sediments. Experiments were performed to examine the factors controlling degradation of pesticides and other organic compounds in soil. Degradation, sorption, and volatilization processes were apparently coupled in soil. Volatilization of the herbicide clomazone increased when degradation was eliminated by sterilization. Clomazone in soil water was preferentially utilized by microorganisms first, followed by slow release of clomazone from the solid phase to replace that lost from solution. During the course of conducting experiments on pesticide degradation, it became necessary to develop or adapt new methodology. For example, we developed a procedure for labeling nitrogen in the atrazine ring with a stable isotope, and discovered new chemistry for measurement of ammonium in soil and water. Such advances are important to research in other laboratories as well as our own. Studies were conducted on a newly registered herbicide, cloransulam- methyl, which has similar degradation properties across a wide range of soil types and conditions. The herbicide exhibited a pattern of temperature dependence similar to that observed in previous years with the herbicide clomazone. Degradation of the compound exhibited little dependence on soil moisture content, and the compound appeared to undergo significant non-biological degradation. The results of these studies will help identify proper seasonal windows for use of this compound with minimal negative environmental consequences. We examined sorption and degradation of the herbicide, isoxaflutole in soils of various organic matter content. Results showed that the herbicide is rapidly transformed to the herbicidally active product, diketonitrile. The parent herbicide remains sorbed to soil under dry conditions, and is rapidly degraded to release the diketonitrile when the soil is rewetted. These findings help explain the unusual rechargeable activity of this herbicide, in which the herbicide appears to be reactivated by rainfall immediately following dry periods. The ability of the aquatic plant, hornwort to remove herbicides from water was examined over a range of light and nutritional conditions. Both the plant and microorganisms living on the plant's surfaces appeared to contribute to this process. These observations suggest that aquatic plants offer a promising alternative for remediation of pesticide contamination in waterways. Factors that limit availability of herbicides to microorganisms, such as soil sorption, or cellular uptake barriers, may contribute to herbicide persistence. The effects of ionization (formation of a charged molecule) of herbicides and model pollutants on uptake of the compounds by numerous species of bacteria was examined in pure culture using a range of pH conditions expected in the environment. As indicated by our previous findings, bacteria preferentially take up herbicides in their unionized (neutral) forms, and when these observations were then compared with the effects of ionization on adsorption of these compounds by soil solids, the results indicated that pH may have profound effects on both persistence and mobility of some herbicides in the environment. These findings are important to understanding variability in microbiological degradation of herbicides in the environment. Inhibition of soil microorganisms by herbicides has been reported sporadically in the literature, though mechanisms of inhibition and development of microbial resistance to herbicides have seldom been addressed in such studies. We examined the ecology of nitrification and herbicide biodegradation in the presence of mixtures of herbicides containing one or more components with anti-microbial properties. The results showed that, for some bacteria possessing enzymes sensitive to a particular herbicide, whole cells were insensitive due to permeability barriers, and in the field, we observed evidence for development of resistance of soil bacteria to certain inhibitory herbicides over time. These findings demonstrate the possibility of microbial adaptation to the presence of herbicides within a single growing season, thus providing an explanation for non-recurring persistence of some herbicides when first added as a component of a mixture, and may lead to management strategies for limiting herbicide carryover damage to crops in rotations. Environmental and toxicological characterization of herbicides is performed prior to any approved environmental release, though for practical and economic reasons, such information is too limited to predict behavior in all possible environmental situations. It is thus necessary to conduct additional studies on recently introduced compounds not only in anticipation of potential problems, but also to facilitate optimal use practices through a better understanding of behavior of the compound in the environment. Isoxaflutole is a recently registered herbicide representing a small class with a novel mode of action. The herbicide has some unusual features, including a highly reactive parent compound that is rapidly converted to an active herbicide product. Fundamental chemical properties, such as solubility and affinity for soil of the parent compound and the active form are quite different, leading to some difficulty in predicting both environmental and herbicidal behavior. Using advances made previously in the study of the soil sorption of this compound, we conducted studies that characterized the complex behavior of the compound in soil systems. The results explained one of the most unusual properties of the herbicide, the tendency to exhibit resurgent activity following precipitation. This behavior was found to be due to protection of the parent compound from activation, degradation, and leaching in dry soil owing to soil sorption. Upon rewetting, the parent compound is released from the soil surface and activated by exposure to the soil solution. The findings also showed the nature of the environmental behavior of the active product and a key, inactive degradation product. These findings will provide a better framework for the use of isoxaflutole, and may allow users to take advantage of the unusual behavior of the compound while guarding against potential negative environmental effects. 6. What science and/or technologies have been transferred and to whom? When is the science and/or technology likely to become available to the end- user (industry, farmer, other scientists)? What are the constraints, if known, to the adoption and durability of the technology products? Owing to the basic nature of much of the research, initial users are expected to be mostly scientists. Evidence for incorporation of the findings in approaches taken by the scientific community can be taken from an exponential increase in citations of products of this work in Science Citation Index over the life of the CRIS, as well as follow up research projects by other scientists in the areas of use of atrazine as an N source, and reduction of nitroaniline herbicides by reduced soil iron species. Agricultural industry consumers are made aware of the work through presentation of research findings and attendance of unit representatives at the University of Illinois Open House, Agronomy Day, and other field days, held each year. Our interactive approach to designing and conducting research allows us to share plans and results with other scientists from ARS, universities, and industry. These discussions guide our research, and provide insight to both public and private sector scientists seeking solutions to carryover injury and water contamination problems. It is anticipated that the remediation approaches for nitroaniline herbicides will be at a stage during FY 2005 that will be suitable for presentation to growers and chemical industry professionals. However, most of the other research results for this CRIS will likely undergo further development by applied scientists prior to adoption by producers. The results obtained in FY 2004 are expected to impact strategies for herbicide use over the next 5 years. 7. List your most important publications in the popular press and presentations to organizations and articles written about your work. Maxwell, J., and Sims, G. K. Life Beneath Your Feet. ACES Open House, University of Illinois, March 11-12, 2003. A staffed, interactive presentation of microorganisms and their functions in soil and water. Merrick, K. Jerry Sims: Interview with leading USDA-ARS researcher. Illinois Technograph Engineering Magazine, Vol. 117 (4):16-17. Illini Media, Urbana, IL. 2002.

Impacts
(N/A)

Publications

  • Marsh, K., Mulvaney, R.L., Sims, G.K. 2003. Availability of urea to autotrophic ammonia oxidizers as related to the fate of 14C- and 15N-urea in soil. [abstract] In: Abstracts of the 103rd Annual Meeting of the American Society for Microbiology. Washington, DC. Number N-025. p. 402- 2003.
  • Sims, G.K., Potera, R., Tranel, P., Riechers, D. 2003. Uptake of herbicides by soil bacteria. [abstract]. Society for Environmental Toxicology and Chemistry. 24th Annual Meeting in North America. Austin, TX. No. PT-026. Annual Meeting Abstract Book. No. p. 194.
  • Sims, G.K., Cupples, A.M. 2004. Role of exogenous inorganic N on biodegradation of N- heterocycles in environmental matrices. [abstract]. In: Abstracts of the 104th Annual Meeting of the American soceity for Microbiology. New Orleans, LA. No. Q-290.


Progress 10/01/02 to 09/30/03

Outputs
1. What major problem or issue is being resolved and how are you resolving it? Weed management is one of the most critical components of successful crop production. At present, herbicides are the predominant tools for weed control in major crops in the U.S. Widespread occurrence of agricultural chemicals in natural waters has stimulated interest in reducing or replacing the role of herbicides in agricultural management programs. Since effective alternatives to herbicides are not routinely available for use in most major crops, it is essential that present weed management practices be adapted in order to minimize the input of and offsite movement of herbicides. Herbicides vary widely in physical, chemical, and biological properties, as well as the manner in which they are used. These differences in properties result in variability in persistence (failure to decompose in the environment) and movement of herbicides away from the use area. Present approaches for evaluating environmental fate of pesticides focus on individual fate mechanisms, and usually ignore interactions among processes (coupled processes). This project is involved in the evaluation of interacting fate processes and characterization of the factors controlling these processes for individual herbicides and closely related groups of herbicides. If we understand how the processes are coupled, and how these systems of coupled processes respond to environmental conditions, we can construct models that describe the complex and often unpredictable behavior of herbicides in the environment. The project also examines fundamental processes in biologically based approaches for weed control and remediation of herbicide contamination. 2. How serious is the problem? Why does it matter? Difficulties in predicting the behavior of agricultural chemicals in the environment have resulted in contamination of natural waters, soil, and even air with agricultural chemicals. In addition, sporadic cases of herbicide carryover on the farm threaten sensitive crops in rotations. Better understanding of herbicide behavior is essential not only for developing management strategies that reduce environmental impacts of agriculture, but also to develop decision aids that protect growers from crop injury by better predicting herbicide carryover. 3. How does it relate to the National Program(s) and National Program Component(s) to which it has been assigned? National Program 202, Soil Quality Management (60%) Soil microorganisms are essential in the natural processes that maintain soil and water quality, and are the major tool used to clean up contaminated soils. Microorganisms are also key players in the natural detoxification and degradation of herbicides. Because of the complexity of biological and non-biological processes involved in herbicide fate, we must identify the factors that control these processes in order to develop weed management practices that protect our soil resources. National Program 201, Water Quality Management (40%) Maintenance of water quality requires improved management practices. This goal is accomplished in part through the use of decision support systems based on a better understanding of the factors influencing the behavior of herbicides in the environment. This research identifies the factors controlling biological and nonbiological processes in the fate of herbicides, as well as the interactions among these processes. The results are incorporated into models that contribute to the development of decision aids for protecting the Nation's water resources. 4. What were the most significant accomplishments this past year? A. A. Single most significant accomplishment during FY 2003: Environmental and toxicological characterization of herbicides is performed prior to any approved environmental release, though for practical and economic reasons, such information is too limited to predict behavior in all possible environmental situations. It is thus necessary to conduct additional studies on recently introduced compounds not only in anticipation of potential problems, but also to facilitate optimal use practices through a better understanding of behavior of the compound in the environment. Isoxaflutole is a recently registered herbicide representing a small class with a novel mode of action. The herbicide has some unusual features, including a highly reactive parent compound that is rapidly converted to an active herbicide product. Fundamental chemical properties, such as solubility and affinity for soil of the parent compound and the active form are quite different, leading to some difficulty in predicting both environmental and herbicidal behavior. Using advances made previously in the study of the soil sorption of this compound, we conducted studies that characterized the complex behavior of the compound in soil systems. The results explained one of the most unusual properties of the herbicide, the tendency to exhibit resurgent activity following precipitation. This behavior was found to be due to protection of the parent compound from activation, degradation, and leaching in dry soil owing to soil sorption. Upon rewetting, the parent compound is released from the soil surface and activated by exposure to the soil solution. The findings also showed the nature of the environmental behavior of the active product and a key, inactive degradation product. These findings will provide a better framework for the use of isoxaflutole, and may allow users to take advantage of the unusual behavior of the compound while guarding against potential negative environmental effects. B. Other significant accomplishment(s), if any: none. C. Significant activities that support special target populations: none. 5. Describe the major accomplishments over the life of the project, including their predicted or actual impact. In prior years, laboratory studies demonstrated the use of the herbicide atrazine as a nitrogen source by soil microorganisms, and that microbial degradation of atrazine may be in part prevented by the presence of nitrogen fertilizers in some organisms and in soil. Thus, one should consider the role of atrazine as a microbial N source when predicting the compound's fate in the environment. Studies with trifluralin strongly implicated a role of microbially modified iron minerals in the anaerobic (absence of oxygen) fate of this herbicide, and may account for rapid deactivation of this and other dinitroaniline herbicides in wet soils and sediments. Experiments were performed to examine the factors controlling degradation of pesticides and other organic compounds in soil. Degradation, sorption, and volatilization processes were apparently coupled in soil. Volatilization of the herbicide clomazone increased when degradation was eliminated by sterilization. Clomazone in soil water was preferentially utilized by microorganisms first, followed by slow release of clomazone from the solid phase to replace that lost from solution. During the course of conducting experiments on pesticide degradation, it became necessary to develop or adapt new methodology. For example, we developed a procedure for labeling nitrogen in the atrazine ring with a stable isotope, and discovered new chemistry for measurement of ammonium in soil and water. Such advances are important to research in other laboratories as well as our own. Studies were conducted on a newly registered herbicide, cloransulam- methyl, which has similar degradation properties across a wide range of soil types and conditions. The herbicide exhibited a pattern of temperature dependence similar to that observed in previous years with the herbicide clomazone. Degradation of the compound exhibited little dependence on soil moisture content, and the compound appeared to undergo significant non-biological degradation. The results of these studies will help identify proper seasonal windows for use of this compound with minimal negative environmental consequences. We examined sorption and degradation of the herbicide, isoxaflutole in soils of various organic matter content. Results showed that the herbicide is rapidly transformed to the herbicidally active product, diketonitrile. The parent herbicide remains sorbed to soil under dry conditions, and is rapidly degraded to release the diketonitrile when the soil is rewetted. These findings help explain the unusual rechargeable activity of this herbicide, in which the herbicide appears to be reactivated by rainfall immediately following dry periods. The ability of the aquatic plant, hornwort to remove herbicides from water was examined over a range of light and nutritional conditions. Both the plant and microorganisms living on the plant's surfaces appeared to contribute to this process. These observations suggest that aquatic plants offer a promising alternative for remediation of pesticide contamination in waterways. Factors that limit availability of herbicides to microorganisms, such as soil sorption, or cellular uptake barriers, may contribute to herbicide persistence. The effects of ionization (formation of a charged molecule) of herbicides and model pollutants on uptake of the compounds by numerous species of bacteria was examined in pure culture using a range of pH conditions expected in the environment. As indicated by our previous findings, bacteria preferentially take up herbicides in their unionized (neutral) forms, and when these observations were then compared with the effects of ionization on adsorption of these compounds by soil solids, the results indicated that pH may have profound effects on both persistence and mobility of some herbicides in the environment. These findings are important to understanding variability in microbiological degradation of herbicides in the environment. Inhibition of soil microorganisms by herbicides has been reported sporadically in the literature, though mechanisms of inhibition and development of microbial resistance to herbicides have seldom been addressed in such studies. We examined the ecology of nitrification and herbicide biodegradation in the presence of mixtures of herbicides containing one or more components with anti-microbial properties. The results showed that, for some bacteria possessing enzymes sensitive to a particular herbicide, whole cells were insensitive due to permeability barriers, and in the field, we observed evidence for development of resistance of soil bacteria to certain inhibitory herbicides over time. These findings demonstrate the possibility of microbial adaptation to the presence of herbicides within a single growing season, thus providing an explanation for non-recurring persistence of some herbicides when first added as a component of a mixture, and may lead to management strategies for limiting herbicide carryover damage to crops in rotations. 6. What do you expect to accomplish, year by year, over the next 3 years? This project has four major objectives, which include: (1) identifying mechanisms involved in sporadic occurrences of persistence of herbicides; (2) determining the role of microbial inhibition in the biodegradation of mixtures of herbicides containing one or more components with anti- microbial properties; (3) developing practical approaches to enhance degradation of xenobiotics used in agricultural production in order to limit off-target impacts of these compounds, and; (4) identifying the major components of weed seeds accessed by microorganisms during seed decay, as well as factors that regulate decay of these seeds. Anticipated practical outcomes include predictive models/decision aids that minimize undesirable effects of herbicides, improved weed management practices that utilize less chemical input, and strategies for remediation of herbicide spills and runoff. During the upcoming year (FY2004), we will continue work on herbicide remediation (part of objective 3) using a microbial rather than phytoremediation approach. Greater advances in this area are expected in part owing to a new collaborative effort developed with the USDA-ARS National Soil Erosion Laboratory in Lafayette, IN. We will continue to work on this objective and objective 4 (microbial decay of weed seeds) through the duration of the current project. 7. What science and/or technologies have been transferred and to whom? When is the science and/or technology likely to become available to the end- user (industry, farmer, other scientists)? What are the constraints, if known, to the adoption and durability of the technology products? Research findings are shared with individual producers and industry scientists through attendance at the University of Illinois Open House, Agronomy Day, and other field days, held each year. During FY 2003, we significantly improved previously reported interactive exhibits on soil microorganisms and presented them to a large audience at the University of Illinois, ACES Open House. To enhance participation, we developed a card game based on the principals of microbial ecology. This game is presently under consideration for development by the American Society for Microbiology. Our interactive approach to designing and conducting research allows us to share plans and results with other scientists from ARS, universities, and industry. These discussions guide our research, and provide insight to both public and private sector scientists seeking solutions to carryover injury and water contamination problems. During FY 2003, as individual research projects reached a stage in which transfer of information outside the scientific community became practical, the information was provided to other scientists through conferences and publications. Because of the basic nature of the research, results will likely undergo further development by applied scientists prior to adoption by producers. The results obtained in FY 2003 are expected to impact strategies for herbicide use over the next 3-5 years. 8. List your most important publications in the popular press and presentations to organizations and articles written about your work. (NOTE: This does not replace your peer-reviewed publications listed below). Sims, G.K. 2002. Soil degradation. McGraw Hill Encyclopedia of Science and Technology, 9th Ed. McGraw Hill, New York. V. 16.

Impacts
(N/A)

Publications

  • Rupassara, S.I., Larson, R.A., Sims, G.K., Marley, K.A. Degradation of atrazine by hornwort in aquatic systems. Bioremediation Journal. 2002. v. 6. p. 217-224.
  • Taylor-Lovell, S., Sims, G.K., Wax, L.M. 2002. Effect of moisture, temperature, and biological activity on the degradation of isoxaflutole in soil. Journal of Agricultural Food Chemistry. v. 50(20). p. 5626-5633.


Progress 10/01/01 to 09/30/02

Outputs
1. What major problem or issue is being resolved and how are you resolving it? Weed management is one of the most critical components of successful crop production. At present, herbicides are the predominant tools for weed control in major crops in the United States. Widespread occurrence of agricultural chemicals in natural waters has stimulated interest in reducing or replacing the role of herbicides in agricultural management programs. Since effective alternatives to herbicides are not routinely available for use in most major crops, it is essential that present weed management practices be adapted in order to minimize the input of and offsite movement of herbicides. Herbicides vary widely in physical, chemical, and biological properties, as well as the manner in which they are used. These differences in properties result in variability in persistence (failure to decompose in the environment) and movement of herbicides away from the use area. Present approaches for evaluating environmental fate of pesticides focus on individual fate mechanisms, and usually ignore interactions among processes (coupled processes). This project is involved in the evaluation of interacting fate processes and characterization of the factors controlling these processes for individual herbicides and closely related groups of herbicides. If we understand how the processes are coupled, and how these systems of coupled processes respond to environmental conditions, we can construct models that describe the complex and often unpredictable behavior of herbicides in the environment. The project also examines fundamental processes in biologically based approaches for weed control and remediation of herbicide contamination. 2. How serious is the problem? Why does it matter? Difficulties in predicting the behavior of agricultural chemicals in the environment have resulted in contamination of natural waters, soil, and even air with agricultural chemicals. In addition, sporadic cases of herbicide carryover on the farm threaten sensitive crops in rotations. Better understanding of herbicide behavior is essential not only for developing management strategies that reduce environmental impacts of agriculture, but also to develop decision aids that protect growers from crop injury by better predicting herbicide carryover. 3. How does it relate to the national Program(s) and National Program Component(s) to which it has been assigned? National Program 202, Soil Quality Management (60%) Soil microorganisms are essential in the natural processes that maintain soil and water quality, and are the major tool used to clean up contaminated soils. Microorganisms are also key players in the natural detoxification and degradation of herbicides. Because of the complexity of biological and non-biological processes involved in herbicide fate, we must identify the factors that control these processes in order to develop weed management practices that protect our soil resources. National Program 201, Water Quality Management (40%) Maintenance of water quality requires improved management practices. This goal is accomplished in part through the use of decision support systems based on a better understanding of the factors influencing the behavior of herbicides in the environment. This research identifies the factors controlling biological and non-biological processes in the fate of herbicides, as well as the interactions among these processes. The results are incorporated into models that contribute to the development of decision aids for protecting the Nation's water resources. 4. What was your most significant accomplishment this past year? A. Single Most Signicicant Accomplishments during FY 2002: Inhibition of soil microorganisms by herbicides has been reported sporadically in the literature, though mechanisms of inhibition and development of microbial resistance to herbicides have seldom been addressed in such studies. We examined the ecology of nitrification and herbicide biodegradation in the presence of mixtures of herbicides containing one or more components with anti-microbial properties. The results showed that, for some bacteria possessing enzymes sensitive to a particular herbicide, whole cells were insensitive due to permeability barriers, and in the field, we observed evidence for development of resistance of soil bacteria to certain inhibitory herbicides over time. These findings demonstrate the possibility of microbial adaptation to the presence of herbicides within a single growing season, thus providing an explanation for non-recurring persistence of some herbicides when first added as a component of a mixture, and may lead to management strategies for limiting herbicide carryover damage to crops in rotations. B. Other significant accomplishment(s), if any: none. C. Significant activities that support special target populations: none. 5. Describe your major accomplishments over the life of the project, including their predicted or actual impact? In prior years, laboratory studies demonstrated the use of the herbicide atrazine as a nitrogen source by soil microorganisms, and that microbial degradation of atrazine may be in part prevented by the presence of nitrogen fertilizers in some organisms and in soil. Thus, one should consider the role of atrazine as a microbial N source when predicting the compound's fate in the environment. Studies with trifluralin strongly implicated a role of microbially modified iron minerals in the anaerobic (absence of oxygen) fate of this herbicide, and may account for rapid deactivation of this and other dinitroaniline herbicides in wet soils and sediments. Experiments were performed to examine the factors controlling degradation of pesticides and other organic compounds in soil. Degradation, sorption, and volatilization processes were apparently coupled in soil. Volatilization of the herbicide clomazone increased when degradation was eliminated by sterilization. Clomazone in soil water was preferentially utilized by microorganisms first, followed by slow release of clomazone from the solid phase to replace that lost from solution. During the course of conducting experiments on pesticide degradation, it became necessary to develop or adapt new methodology. For example, we developed a procedure for labeling nitrogen in the atrazine ring with a stable isotope, and discovered new chemistry for measurement of ammonium in soil and water. Such advances are important to research in other laboratories as well as our own. Studies were conducted on a newly registered herbicide, cloransulam- methyl, which has similar degradation properties across a wide range of soil types and conditions. The herbicide exhibited a pattern of temperature dependence similar to that observed in previous years with the herbicide clomazone. Degradation of the compound exhibited little dependence on soil moisture content, and the compound appeared to undergo significant non-biological degradation. The results of these studies will help identify proper seasonal windows for use of this compound with minimal negative environmental consequences. We examined sorption and degradation of the herbicide, isoxaflutole in soils of various organic matter content. Results showed that the herbicide is rapidly transformed to the herbicidally active product, diketonitrile. The parent herbicide remains sorbed to soil under dry conditions, and is rapidly degraded to release the diketonitrile when the soil is rewetted. These findings help explain the unusual rechargeable activity of this herbicide, in which the herbicide appears to be reactivated by rainfall immediately following dry periods. The ability of the aquatic plant, hornwort to remove herbicides from water was examined over a range of light and nutritional conditions. Both the plant and microorganisms living on the plant's surfaces appeared to contribute to this process. These observations suggest that aquatic plants offer a promising alternative for remediation of pesticide contamination in waterways. Factors that limit availability of herbicides to microorganisms, such as soil sorption, or cellular uptake barriers, may contribute to herbicide persistence. The effects of ionization (formation of a charged molecule) of herbicides and model pollutants on uptake of the compounds by numerous species of bacteria was examined in pure culture using a range of pH conditions expected in the environment. As indicated by our previous findings, bacteria preferentially take up herbicides in their unionized (neutral) forms, and when these observations were then compared with the effects of ionization on adsorption of these compounds by soil solids, the results indicated that pH may have profound effects on both persistence and mobility of some herbicides in the environment. These findings are important to understanding variability in microbiological degradation of herbicides in the environment. 6. What do you expect to accomplish, year by year, over the next 3 years? This project has four major objectives, which include: (1) identifying mechanisms involved in sporadic occurrences of persistence of herbicides; (2) determining the role of microbial inhibition in the biodegradation of mixtures of herbicides containing one or more components with anti- microbial properties; (3) developing practical approaches to enhance degradation of xenobiotics used in agricultural production in order to limit off-target impacts of these compounds, and; (4) identifying the major components of weed seeds accessed by microorganisms during seed decay, as well as factors that regulate decay of these seeds. Anticipated practical outcomes include predictive models/decision aids that minimize undesirable effects of herbicides, improved weed management practices that utilize less chemical input, and strategies for remediation of herbicide spills and runoff. During the upcoming year (FY2003), we will complete our characterization of the role of uptake of herbicides in biological degradation (component of objective 1) and finalize our work on phytoremediation (part of objective 3). Since the vacancy in microbiology at the location has been filled, we can now initiate work on objective 4 (microbial decay of weed seeds). These objectives will continue to be addressed in FY 2004. 7. What technologies have been transferred and to whom? When is the technology likely to become available to the end user (industry, farmer other scientist)? What are the constraints, if known, to the adoption durability of the technology? Research findings are shared with individual producers and industry scientists through attendance at the University of Illinois Open House, Agronomy Day, and other field days, held each year. During FY 2002, two interactive exhibits on soil microorganisms were developed and presented to a large audience at the University of Illinois, ACES Open House. Our interactive approach to designing and conducting research allows us to share plans and results with other scientists from ARS, universities, and industry. These discussions guide our research, and provide insight to both public and private sector scientists seeking solutions to carryover injury and water contamination problems. During FY 2002, as individual research projects reached a stage in which transfer of information outside the scientific community became practical, the information was provided to other scientists through conferences and publications. Because of the basic nature of the research, results will likely undergo further development by applied scientists prior to adoption by producers. The results obtained in FY 2002 are expected to impact strategies taken by chemical manufacturers over the next 3-5 years. 8. List your most important publications and presentations, and articles written about your work (NOTE: this does not replace your review publications which are listed below) Sims, G.K. Soil degradation. AccessScience @ McGraw Hill. Available from: http://www.accessscience.com.

Impacts
(N/A)

Publications

  • Xu, J.C., Stucki, J.W., Wu, J., Kostka, J.E., Sims, G.K. Fate of atrazine and alachlor in redox-treated ferruginous smectite. Journal of Environmental Toxicology and Chemistry. 2001. v. 20. p. 2717-2724.
  • Hultgren,R.P., Hudson, R.J.M., Sims, G.K. Effects of soil pH and soil water content on Prosulfuron dissipation. Journal of Agricultral Feed Chemistry. 2002. v. 5. p. 3236-3243.
  • Crawford, J.J., Sims, G.K., Simmons, F.W., Wax, L.M., Freedman, D.L. Dissipation of the herbicide (14C) dimethenamid under anaerobic aquatic conditions in flooded soil microcosms. Journal of Agricultral Feed Chemistry. 2002. v. 50. p. 1483-1491.


Progress 10/01/00 to 09/30/01

Outputs
1. What major problem or issue is being resolved and how are you resolving it? Weed management is one of the most critical components of successful crop production. At present, herbicides are the predominant tools for weed control in major crops in the United States. Widespread occurrence of agricultural chemicals in natural waters has stimulated interest in reducing or replacing the role of herbicides in agricultural management programs. Since effective alternatives to herbicides are not routinely available for use in most major crops, it is essential that present weed management practices be adapted in order to minimize the input of and offsite movement of herbicides. Herbicides vary widely in physical, chemical, and biological properties, as well as the manner in which they are used. These differences in properties result in variability in persistence (failure to decompose in the environment) and movement of herbicides away from the use area. Present approaches for evaluating environmental fate of pesticides focus on individual fate mechanisms, and usually ignore interactions among processes (coupled processes). This CRIS unit is involved in the evaluation of interacting fate processes and characterization of the factors controlling these processes for individual herbicides and closely related groups of herbicides. If we understand how the processes are coupled, and how these systems of coupled processes respond to environmental conditions, we can construct models that describe the complex and often unpredictable behavior of herbicides in the environment. The CRIS also examines fundamental processes in biologically based approaches for weed control and remediation of herbicide contamination. 2. How serious is the problem? Why does it matter? Difficulties in predicting the behavior of agricultural chemicals in the environment have resulted in contamination of natural waters, soil, and even air with agricultural chemicals. In addition, sporadic cases of herbicide carryover on the farm threaten sensitive crops in rotations. Better understanding of herbicide behavior is essential not only for developing management strategies that reduce environmental impacts of agriculture, but also to develop decision aids that protect growers from crop injury by better predicting herbicide carryover. 3. How does it relate to the National Program(s) and National Component(s)? National Program 202, Soil Quality Management (60%) Soil microorganisms are essential in the natural processes that maintain soil and water quality, and are the major tool used to clean up contaminated soils. Microorganisms are also key players in the natural detoxification and degradation of herbicides. Because of the complexity of biological and non-biological processes involved in herbicide fate, we must identify the factors that control these processes in order to develop weed management practices that protect our soil resources. National Program 201, Water Quality Management (40%) Maintenance of water quality requires improved management practices. This goal is accomplished in part through the use of decision support systems based on a better understanding of the factors influencing the behavior of herbicides in the environment. This research identifies the factors controlling biological and non-biological processes in the fate of herbicides, as well as the interactions among these processes. The results are incorporated into models that contribute to the development of decision aids for protecting the Nation's water resources. 4. What were the most significant accomplishments this past year? A. Single Most Significant Accomplishment during FY 2001: Factors that limit availability of herbicides to microorganisms, such as soil sorption, or cellular uptake barriers, may contribute to herbicide persistence. The effects of ionization (formation of a charged molecule)of herbicides and model pollutants on uptake of the compounds by numerous species of bacteria was examined in pure culture using a range of pH conditions expected in the environment. As indicated by our previous findings, bacteria preferentially take up herbicides in their unionized (neutral) forms, and when these observations were then compared with the effects of ionization on adsorption of these compounds by soil solids, the results indicated that pH may have profound effects on both persistence and mobility of some herbicides in the environment. These findings are important to understanding variability in microbiological degradation of herbicides in the environment. B. Other Significant Accomplishment(s), if any: Nothing to report. C. Significant Accomplishments/Activities that Support Special Target Populations: Nothing to report. 5. Describe the major accomplishments over the life of the project including their predicted or actual impact. This is a new project plan replacing 3611-12220-005-00D. The previous project focused on factors influencing herbicide sorption, degradation and bound residue formation. In prior years, laboratory studies demonstrated the use of the herbicide atrazine as a nitrogen source by soil microorganisms, and that microbial degradation of atrazine may be in part prevented by the presence of nitrogen fertilizers in some organisms and in soil. Thus, one should consider the role of atrazine as a microbial N source when predicting the fate of the compound in the environment. Studies with trifluralin strongly implicated a role of microbially modified iron minerals in the anaerobic (absence of oxygen) fate of this herbicide, and may account for rapid deactivation of this and other dinitroaniline herbicides in wet soils and sediments. Experiments were performed to examine the factors controlling degradation of pesticides and other organic compounds in soil. Degradation, sorption, and volatilization processes were apparently coupled in soil. Volatilization of the herbicide clomazone increased when degradation was eliminated by sterilization. Clomazone in soil water was preferentially utilized by microorganisms first, followed by slow release of clomazone from the solid phase to replace that lost from solution. During the course of conducting experiments on pesticide degradation, it became necessary to develop or adapt new methodology. For example, we developed a procedure for labeling nitrogen in the atrazine ring with a stable isotope, and discovered new chemistry for measurement of ammonium in soil and water. Such advances are important to research in other laboratories as well as our own. Studies were conducted on a newly registered herbicide, cloransulam- methyl, which has similar degradation properties across a wide range of soil types and conditions. The herbicide exhibited a pattern of temperature dependence similar to that observed in previous years with the herbicide clomazone. Degradation of the compound exhibited little dependence on soil moisture content, and the compound appeared to undergo significant non-biological degradation. The results of these studies will help identify proper seasonal windows for use of this compound with minimal negative environmental consequences. We examined sorption and degradation of the herbicide, isoxaflutole in soils of various organic matter content. Results showed that the herbicide is rapidly transformed to the herbicidally active product, diketonitrile. The parent herbicide remains sorbed to soil under dry conditions, and is rapidly degraded to release the diketonitrile when the soil is rewetted. These findings help explain the unusual rechargeable activity of this herbicide, in which the herbicide appears to be reactivated by rainfall immediately following dry periods. The ability of the aquatic plant, hornwort to remove herbicides from water was examined over a range of light and nutritional conditions. Both the plant and microorganisms living on the plantts surfaces appeared to contribute to this process. These observations suggest that aquatic plats offer a promising alternative for remediation of pesticide contamination in waterways. 6. What do you expect to accomplish, year by year, over the next 3 years? This project has four major objectives, which include: (1) identifying mechanisms involved in sporadic occurrences of persistence of herbicides; (2) determining the role of microbial inhibition in the biodegradation of mixtures of herbicides containing one or more components with anti- microbial properties; (3) developing practical approaches to enhance degradation of xenobiotics used in agricultural production in order to limit off-target impacts of these compounds, and; (4) identifying the major components of weed seeds accessed by microorganisms during seed decay, as well as factors that regulate decay of these seeds. Anticipated practical outcomes include predictive models/decision aids that minimize undesirable effects of herbicides, improved weed management practices that utilize less chemical input, and strategies for remediation of herbicide spills and runoff. During the upcoming year (FY2002), we will continue our efforts toward characterizing the importance of uptake of herbicides in biological degradation as well as inhibitory effects of herbicides on degradation of herbicide partners (components of objectives 1 and 2) and finalize our work on phytoremediation (part of objective 3). These objectives will continue to be addressed in FY 2003 and 2004. Upon filling a vacancy in microbiology at the location (anticipated during FY 2002), we plan to initiate work on objective 4. 7. What science and/or technologies have been transferred and to whom? When is the science and/or technology likely to become available to the end user (industry, farmer, other scientists)? What are the constraints if known, to the adoption & durability of the technology product? Research findings are shared with individual producers and industry scientists through attendance at the University of Illinois Agronomy Day and other field days, held each year. Our interactive approach to designing and conducting research allows us to share plans and results with other scientists from ARS, universities, and industry. These discussions guide our research, and provide insight to both public and private sector scientists seeking solutions to carryover injury and water contamination problems. During FY 2001, as individual research projects reached a stage in which transfer of information outside the scientific community became practical, the information was provided to other scientists through conferences and publications. Because of the basic nature of the research, results will likely undergo further development by applied scientists prior to adoption by producers. The results obtained in FY 2001 are expected to impact strategies taken by chemical manufacturers over the next 3-5 years. 8. List your most important publications in the popular press (no abstracts) and presentations to non-scientific organizations and articles written about your work (NOTE: this does not replace your peer-reviewed publications which are listed below)

Impacts
(N/A)

Publications

  • Sims, G.K., Hultgren, R.P., Cupples, A.M., Hudson, R.J. Role of ionization in bacterial uptake and soil sorption of agrochemicals. Proceedings of the International Conference on Groundwater Quality. 2001. p. 268-270.