Duration: 10/01/2000 to 09/30/2005

Administrative Advisor(s):

NIFA Reps:

Non-Technical Summary

Statement of Issues and Justification

STATEMENT OF PROBLEM:
Agricultural activity while essential in meeting the dietary needs of the world can result in the contamination of soil, air, and water resources. Identifying and adequately quantifying the chemical and biological processes that control the behavior of organic chemicals in the environment is imperative towards improving pesticide management, minimizing contamination of our natural resources, and remediating contaminated environments.

JUSTIFICATION:
Use of organic chemicals by all sectors of the economy has resulted in widespread contamination of soil, air, and water. Because chemical technology is generally recognized as having great societal benefit compared to the risks, it is critical that approaches and tools for managing chemical use are developed in order to minimize future contamination and to remediate contaminated environments. Evaluating and quantifying the environmental behavior of organic chemicals is vital towards the development of sound strategies for ensuring sustainable agriculture and protecting natural resource systems.
A major societal concern regarding chemical contamination is pesticide residues in our environment and food. Pesticide use will continue to decline as a result of improved integrated pest management (IPM) systems and development of sustainable, integrated farming systems. Nevertheless, use of pesticides will remain a mainstay within production systems, especially for the many crops for which IPM systems have not been developed. Research is needed on identifying efficient pesticide use practices with minimal environmental impacts. Newly developed pesticides, many of which are applied at rates one-tenth or less of conventional pesticides, are often highly toxic to nontarget crops or aquatic organisms; thus, knowledge is needed of the transport and fate of these substances.
In addition to pesticides, the environmental fate of pharmaceutically active substances is a rising concern. Pharmaceutical substances, which are designed to cause a biological effect and are usually organic in nature, have a high potential for being a major player in endocrine disruption. Almost half of the fifty million pounds of antibiotics produced annually in the United States is used for agriculture, with the majority being used as feed additives for growth promotion. With increases in the intensive use of antibiotics in concentrated animal feeding operations and land application of manure, there are concerns that excreted pharmaceuticals will migrate in the environment with potential impacts on water supplies and the production of antibiotic-resistant microbial populations. Recent research has shown a high percentage of multiple-antibiotic resistant microbial populations in litter from broiler houses. In large animal feeding operations antibiotics could be highly concentrated in animal wastes and associated lagoons. Little effort to date has been put forth with regards to the potential of these organic substances impacting ground and surface waters, their impact on soil microbial communities, and their overall persistence in the environment. A better understanding of the environmental fate of antibiotics is needed to assess the environmental risk involved in exposing animal wastes to the environment.
Organic chemicals not necessarily identified with the agricultural industry are also of interest. For example, petroleum products or "inert" materials (e.g. solvents, emulsifiers) are present in pesticide formulations and are commonly used on farms. Also, as areas of urban and rural land use increasingly overlap, these often conflicting communities impact one another through their chemical use patterns. The principles governing the behavior of organic chemicals in the environment are the same regardless of how these chemicals are used. Therefore, both urban and rural sectors of the economy can benefit from basic and applied studies of all organic chemicals whether they are used in agro-ecosystems or are associated with hazardous waste sites. Over the last several decades, the agricultural science community has conducted most of the research on the environmental behavior of organic chemicals regardless of their source. Much of the current research on the environmental behavior of industrial chemicals is dependent on basic principles originally derived in the study of pesticides, some of which resulted from research by W-82 members.
The fate and accumulation of organic compound residues are mediated by various, often tightly coupled, processes including advection and diffusion, sorption and desorption, biodegradation, and chemical reactions. These processes occur within and between intimately associated environmental compartments (soil, water, air, and biota). For example, chemical interactions with the soil controls chemical persistence, release into water and air, and bioavailability, which impact pesticide efficacy, degradation, and off-site transport. Because of the complexity of interactions among chemical properties, environmental compartments, and spatial and temporal scales, research involving environmental pollution requires a multi-disciplinary approach. A unique strength of the W-82 committee is the close research collaboration among its members from different scientific disciplines who, outside the committee, do not have sufficient opportunity to communicate with one another. W-82 provides a forum where specialists in mechanisms of chemical behavior, microbial ecology, transport behavior, mathematical modeling, and field assessment techniques can come together, and exchange information gleaned from individual or cooperative research efforts. Such cooperative efforts between research groups representing different expertise and diverse geographical areas are imperative developing appropriate management techniques for minimizing environmental contamination and thus risk.
The goal of W-82 research is to minimize environmental contamination from pesticides and other organic chemicals. W-82 proposes to carry out a cooperative and interdependent research program that elucidates fundamental mechanisms of chemical behavior and applies this knowledge to different spatial and temporal scales. In combination with mechanistic models, the principles of chemical behavior will be integrated to form management models and propose and assess best management techniques. Research carried out by W-82 will be useful in the continued development of best management practices for minimizing environmental contamination, as well as, the development of efficient and comparatively inexpensive strategies for remediating contaminated environments. Results of the research proposed by W-82 will be applicable to agro-ecosystems in addition to urban systems, and will fulfill USDA needs with regards to protection of water quality and development of integrated agricultural systems as well as the USDA mission for serving the dominant urban sector of our economy. By developing better management techniques the risks of adverse environmental and health effects of our chemical technology will be greatly minimized.

Related, Current and Previous Work

Interfacial Transfer Processes

Our understanding of interfacial transfer processes impacting the distribution of organic chemicals in the environment has progressed greatly over the past two decades. Interfacial transfer includes partitioning between air, water, soil particles, and microorganisms. Sorption by organic matter (humus) and clay minerals are key processes affecting the mobility of pesticides and other chemicals in soils (Meyer and Thurman, 1996; Koskinen and Clay, 1997). Organic matter can be bound to minerals, and humus-coated minerals can play a very important role as sorbents (Kordel et al., 1997; Celis et al., 1997, 1998; 1999a,b; Cox et al., 1998). The interactions of chemicals with sorbed and in some cases dissolved (or colloidal) humus largely determine their ability to move through the soil profile (Meyer and Thurman, 1996; Koskinen and Clay, 1997; Seta and Karathanasis, 1997; Chien et al., 1997). Research is needed that focuses on the interactions of chemicals with such materials. Despite decades of research on these interactions, there are a number of issues that remain unresolved (Pignatello, 2000). These include: the mechanism of sorption by natural organic matter and organoclays, hysteresis, prediction of sorption/desorption kinetics, the relationship between sorption/desorption and bioavailability, and the influence of adjuvants in pesticide formulations on pesticide transport.

Sorption may be affected by the residence time in soil (Cox et al., 1998; McCall and Agin, 1985; Pignatello and Huang, 1991: Shelton and Parkin, 1991). Hysteresisthe asymmetry in the sorption isotherm between the forward (uptake) and reverse (desorption) directionsis a vexing problem that has not been satisfactorily explained. There is a need to account for sorption hysteresis in a quantitative way and to understand it mechanistically in order to improve our ability to predict leaching from aged residues. Partitioning of pesticides between particles and water may not be the same in field moist soils than traditional batch slurry systems; as a consequence, the obtained batch sorption parameters may not adequately reflect sorption processes in field moist or unsaturated soil (Celis and Koskinen, 1999; Hance, 1977; Rochette and Koskinen, 1996; Rochette and Koskinen, 1998).

Recently there has been a great deal of interest in sorption/desorption kinetics in relation to biological availability of contaminants in soils (Pignatello and Xing, 1996; Luthy, et al. 1997; Lee et al., 1998). It is known that intraparticle sorption processes reach equilibrium only slowly; that exhaustive water extraction leaves behind an appreciable fraction that strongly resists further desorption; and that the resistant fraction increases with time as the soil-chemical matrix ages. Evidence has emerged linking this resistant fraction to reduced leachability; non-ideal transport in groundwater; reduced bioavailability to bacteria, ecological receptors and humans; and incomplete remediation at polluted sites. Since bioavailability is strongly dependent on desorption rates, and since remediation costs rise exponentially with the degree of removal, studies are critically needed to understand the underlying causes of resistant desorption. In particular, the interaction of organic chemicals with soil organic matter is proving to be more complex than previously realized. Studies are needed to understand this interaction at a fundamental level. Similarly, it has been observed that rainfall soon after pesticide application (i.e., prior to attainment of equilibrium) results in elevated pesticide concentrations in ground and surface water samples, i.e. a flush effect (Wauchope 1987; Wauchope et al. 1990; Dravillas 1993; Dowdy et al., 1998). Many attempts have been made to model pesticide transport and to quantify the flush effect, but results have been less than adequate.

Humus-coated clays and other model sorbents are useful models for studying the complex sorption sites for pesticides and other organics in soils with varying pH and ionic strength conditions (Celis et al., 1997, 1998). Organo-clay formulations have also been used as a means of plume containment at contaminated sites, i.e., and more recently, formulations were developed to reduce alachlor and metolachlor leaching (Polubesova et al., 1997; El-Nahhal et al., 1998, 1999). These formulations were based on montmorillonite preadsorbed with the synthetic organic cations benzyltrimethylammonium (BTMA) and phenyltrimethylammonium (PTMA) to change the clay mineral surface from hydrophilic to hydrophobic, resulting in effective adsorption of hydrophobic herbicides (Xu and Boyd, 1995), thus reducing their soil solution concentration and extending their herbicidal activity. Optimized organo-clay formulations demonstrated slow release of the herbicides to the soil solution, thus restricting herbicide activity to near the top of the soil profile as measured by bioassay (El-Nahhal et al., 1998, 1999). Similar results may be found for herbicides capable of hydrophobic interactions with humus-coated minerals. Additional research with organo-clays is needed to evaluate and optimize the use of such formulations as a means to modulate pesticide release and serve in-situ plume containment strategies, and as model sorbents to improve our ability to predict complex sorption processes.
The use of pesticdes in wetland ecoysytems such as those used in the production of cranberries can be problematic because of the strong likilhood that water flowing through the system will become contaminated. Weed control relies on the use of early season herbicides applied to the soil prior to cranberry shoot growth. Growers have reported efficacy problems with napropamide (Devrinol) as evidenced by the high rates of application required for control. Dichlobenil (Casoron) has performed very unpredictably; in some cases it has caused phytotoxicity to vines and in other situations it has failed to adequately control dodder. Herbicide efficacy can also be greatly affected by adsorption of the active ingredient to soil organic matter (OM), volatilization, and rate of degradation. Early work with dichlobenil indicated that bioactivity was affected by binding with organic matter (OM), which may have also reduced degradation (Miller et al. 1966). Leaving the chemical on the surface without incorporation augmented volatilization; irrigating following application to achieve some incorporation prolonged persistence (Miller et al. 1967). Commonly used pesticides in cranberries, including napropamide, 2,4-D, and carbofuran, have been shown to rapidly degrade upon repeatedly applying the product to soil (Walker and Welch 1991), which has been shown to adversely affect pest control efficacy (Felsot 1989; Wilson and Felsot 1997). In soil from a nearby bog without napropamide use but managed by the same grower, only 10% of the napropamide dissipated. In contrast to napropamide, multiple applications of dichlobenil did not affect degradation rate, which suggests either chemical degradation or volatilization as major loss mechanisms (Felsot and Patten 1997). Under drying conditions, sorption would increase thereby reducing bioavailability while under flooded conditions, bioavailability would be enhanced by desorption, thus enhancing the probability of uptake by cranberry vines with consequent phytotoxicity. Furthermore, growers periodically put a layer of sand on the bog, which may periodically decrease dichlobenil sorption potential, thereby increasing its volatilization and/or bioavailability. Effective pest management in cranberry requires a better understanding of soil-herbicide interactions in wetland-like systems. An understanding of these interactions will allow better predictions of bioavailability, a key determinant of efficacy as well as likelihood for environmental contamination.

Volatilization of pesticides may contribute significantly to air pollution in regions with intensive agricultural production. For instance, a multiple-year monitoring study conducted by the California Air Resource Board showed high concentrations of pesticides, especially soil fumigants, in ambient air near application sites (Baker et al., 1996). Because some soil fumigants are acutely toxic or carcinogenic, excessive emissions may impose hazardous effects on field workers and nearby residents. Thus, it is clearly important to understand fumigant volatilization after application and develop mitigation measures minimize their emissions. The maximum amount of pesticide losses to the atmosphere is determined by the Henrys law constant, i.e., the air-water partition coefficient, and the rate of mass transfer from the air-water, soil-air interface, or through liners used in fumigant application. Henrys law behavior is well known in simple aqueous systems; however, studies are needed to predict air-water partitioning in complex aqueous solutions that exist in soils, estuarine, and fresh-water systems, especially the influence of dissolved and colloidal organic matter (Baker et al., 1996; Breiter et al., 1998). Currently, plastic films are used to tarp the soil surface following soil fumigation; however, these films are relatively permeable to fumigant vapors, allowing a large proportion of the applied mass to escape to the atmosphere. Films with very low permeability are being developed in hopes that with more fumigant containment, fumigant application rates can be decreased and still result in adequate efficacy. The permeability of plastic films must be determined under a variety of environmental conditions to develop management practices that minimize fumigant flux to the atmosphere.

Microbial Degradation & Microbial Communities
Our ability to investigate the soil microbial populations involved in biodegradation has been enhanced with the expansion of molecular tools for describing, and in some cases quantifying, specific microbial populations and communities. A clear understanding of the fate of organic contaminants in the environment depends on an understanding of the biodegradation pathways by which these compounds are transformed, and an understanding of the mechanisms by which genes encoding their metabolism are spread throughout a soil community. Genetic exchange and gene recruitment are likely to be important mechanisms in development of novel pathways for metabolism of newly introduced compounds, such as pesticides. Little is known about how genes encoding pesticide degradation spread among soil bacteria, or of the impact that genetic exchange has on the development of enhanced biodegradation.

Despite numerous years of study, little information is available concerning microbial population and community structure involved in the transformation of pesticides and organic chemicals in soil. Relatively few microorganisms that degrade pollutants have been isolated and characterized. For example, virtually all that is known of the biochemistry and genetics of bacterial naphthalene metabolism was gained from analysis of a limited number of microorganisms, such as Pseudomonas sp. strains, but attention is now turning to metabolism by more diverse gram positive organisms, such as Rhodococcus species. Rhodococcus strains metabolize a range of aromatic hydrocarbons and chlorinated aromatic compounds (Kastner et al., 1994; Finnerty, 1992; Grund et al., 1992; Uz et al., 1999); however, little is known of the pathways or genetics of metabolism by Rhodococcus strains. A similar situation exits for the pesticide atrazine, where despite several years of research there is little information is available concerning the genes involved in the metabolism of atrazine and other s-triazine compounds (Nagy et al., 1995; Shao and Behki, 1995). In a model system developed to study atrazine biodegradation, the first three genes involved in atrazine degradation in Pseudomonas sp. strain ADP have been cloned, sequenced and expressed (de Souza, et al.,1996; 1997; Mandelbaum et al., 1995; Chakrabarty, 1996). We have shown that atrazine degradation genes are plasmid encoded in strain ADP and have investigated the distribution and transfer of these genes in other atrazine degrading bacteria on a global scale (MN). Similar work is being performed with carbofuran as well (FL). Use of genomics will allow us to gain a better understanding of the way in which genes and biodegradation pathways are assembled on plasmids to degrade new anthropogenic compounds.

It is often assumed that the solution phase of a sorbed chemical can be biodegraded by microorganisms. However, there is a significant diversity in the capabilities of microorganisms to degrade contaminants partitioned in, or sorbed by natural organic matter (NOM) (Guerin and Boyd, 1997; Tang et al., 1998). Physiological explanations for such diversity may include variations in attachment and adhesion to NOM surfaces (Harms and Zehnder, 1994; Holm et al., 1992; Neu, 1996), production of biosurfactants (Herman et al., 1997; Noordman et al., 1998), motility, rates of membrane transport, and/or variation in metabolic pathways or enzyme expression leading to variations in mineralization kinetic parameters (Stringfellow and Aitken, 1994). Enrichment strategies in which contaminants are sorbed to organic solid phases may provide a more relevant selection environment, and may eventually lead to a better understanding of the involvement of microorganisms and microbial processes in the mineralization of contaminants in soils.

Soil microbial communities are extraordinarily diverse and it is unknown what proportion of the community is actively engaged in degradation processes in soil. Analysis of phospholipid fatty acids (PLFA) can be used to quantitatively describe and ""fingerprint"" the whole soil community. (Kerger et al., 1986; Dowling et al., 1986, Ringelberg et al, 1989, Olsson et al., 1995, LeChevalier, 1977). Community level, PLFA analysis can distinguish changes in microbial biomass and community structure in soils polluted with heavy metals and organic pollutants (Pennanen et al., 1996, Smith et al., 1986). Recently, 13C-labeled PLFAs have been used resulting from incorporation of stable isotope-labeled C substrates into soil, to provide a way to define the groups of organisms utilizing those substrates (CA).

Soil fumigants are degraded in soil both chemically and microbially. It was reported that in soils that had received repeated applications of fumigants, fumigant degradation was significantly enhanced (Smelt et al., 1989). Understanding biodegradation of fumigants will not only improve our knowledge on the environmental fate of soil fumigants, but may also lead to isolation and identification of fumigant degraders. Application of such biodegraders may, ideally, be used to reduce fumigant contamination of air and/or groundwater. Our early study also showed that amendment of some organic wastes in soil resulted in drastically enhanced fumigant degradation, and the enhancement was mainly due to stimulated microbial degradation (Gan et al., 1998a). It is important to screen and identify organic amendments that are capable of degrading fumigants. Such amendments may be applied in practice for reducing fumigant emissions.

Antibiotics are widely used in animal feeding operations and can be expected to appear in animal wastes. Pharmaceutical substances such as antibiotics are designed to cause a biological effect, and have a high potential for being a major player in endocrine disruption; however, little effort has been put forth with regards to their environmental fate (Halling-Sxrensen et al., 1998). In the past few years, endocrine disruption has become one of EPA's priority research areas (Kavlock, 1999). The majority of research to date has focused on fate of industrial chemicals and their role in endocrine disruption. However, almost half of the fifty million pounds of antibiotics produced annually in the United States is used for agriculture, with the majority of this used as feed additives for growth promotion (Wade and Barkley, 1991). Antibiotics fed to animals are either metabolized or excreted unchanged in the urine and feces (Chiu et al., 1990; Magnussen et al., 1991). In large animal feeding operations antibiotics could be highly concentrated in animal wastes and associated lagoons. In addition, spreading manure on land as both a fertilizer and a disposal strategy is commonly practiced in animal feeding operations (USDA, 1996). With increases in the intensive use of antibiotics in concentrated animal feeding operations and land application of manure, there is concern that excreted pharmaceuticals will migrate in the environment with potential impacts on water supplies and the production of antibiotic-resistant microbial populations. A better understanding the environmental fate of antibiotics from animal waste application, survival and development of antibiotic-resistant microbial population in the environment, and antibiotic-resistance gene transfer among microbial populations are important to assess the environmental risk involved in exposing animal waste to the environment.

Abiotic Transformation Processes

Almost nothing is known about the role of Mn (IV) oxides in the oxidation of herbicides and other pesticides commonly applied to soils (Wolfe et al., 1990). The prevalent view is that pesticide oxidation in natural soils is usually enzyme-catalyzed, not mineral-surface catalyzed (Bollag and Liu, 1990). However, Lehman et al. (1987) and Lehman and Cheng (1988) have demonstrated that phenolic acids are rapidly oxidized abiotically in natural soils in the presence of Mn oxides. Li and Lee (1999) and Li et al. (2000) have demonstrated the reduction of Mn(III) to Mn(II) during transformation of organic amines in sterile soils. A more comprehensive characterization of the abiotic MnO2-catalyzed degradation of atrazine demonstrating that dealkylation proceeds at the same rate with or without O2 and involves no net redox .

Volatilization loss of a fumigant can be reduced if its degradation in soil is accelerated. This has been demonstrated in laboratory column and field micro-plot experiments. Gan et al. (1998b,e) recently discovered that thiosulfate salts can rapidly react with chlorinated compounds including methyl bromide, 1,3-dichloropropene, chloropicrin, methyl iodide and propargyl bromide, and transform these compounds into non-volatile, less toxic ionic species. Because common thiosulfate salts (e.g., ammonium thiosulfate and potassium thiosulfate) are commercial fertilizers, this approach is highly feasible for field application and warrants more study.

CRIS Review of Regional Project Overlap
The proposed research for this regional project combines the study of processes controlling pesticide movement in soil, water, and air with the goal of model development and of providing stakeholders with environmentally sound decision-making strategies that optimize the management of pesticides. A search of currently funded CRIS projects revealed that there are several projects that address pieces of the proposed work, especially the study of transport mechanisms in soil; however, there are no existing projects that encompass all the aspects of the research included in this project.
Interestingly, several of the overlapping projects in the area of transport mechanisms have a W-82 member as the primary investigator. For example, Dr. S. Yates and Dr. J. Gan lead three out of the four existing projects focused on volatilization processes. Dr. J. Pignatello and Dr. W. Inskeep are lead scientists in two out of the six projects on sorption/desorption kinetics. There are also currently three projects that address pesticide movement in soil using a traditional hydrologic approach and soil column leach tests. Additionally, Dr. L. Lee leads one of the two projects on abiotic processes controlling mobility and bioavailability of pesticides in soil. Therefore this regional project team includes a number of outstanding scientists in the area of pesticide transport.
In the area of bioavailability and biotransformation of organic chemical in soil through the study of microbial ecology, most of the projects are focused on remediation of chlorinated and petroleum-based contaminants and not pesticides. And in the area of model predictions of pesticide fate, most funded projects are utilizing existing models and are not developing new models as proposed here.
As a regional project, W-82 has been complementary in focus to the W-45 regional project that is also undergoing renewal. The new project proposal for W-45 is different than W-82 in that its objectives are to 1) identify, develop, and/or validate trace residue analytical methods, immunological procedures, and biomarkers, 2) characterize abiotic and biotic reaction mechanisms, transformation rates, and fate in agricultural and natural ecosystems, 3) determine adverse impacts from agrochemical exposure to cells, organisms, and ecosystems. Therefore, the W-45 project proposal will be more fundamental in nature with an emphasis on a molecular level processes and exposure rates as compared to the W-82 project proposal.

Objectives

1. Characterize and quantify the basic chemical and biological processes controlling the behavior of pesticides, other organic chemicals, and microorganisms in soil, water, and air.
   
2. Integrate chemical and biological process information for use in models applicable across different spatial and temporal scales
   
3. Provide stakeholders with tools for developing strategies to ensure sustainable agriculture and to protect natural resource systems.
   
4. 
   

Methods

Measurement of Progress and Results

Outputs

• The research conducted by W-82 committee members will generate new data that will serve to advance the understanding of environmental fate processes of organic chemicals. W-82 committee members have consistently demonstrated productivity through several hundred publications over the past project periods and are expected to continue the publication of research results in peer-reviewed journal articles, books, book chapters, and technical bulletins as well as commentaries and news briefs. Specific outcomes that are expected include the following: (1) novel laboratory and field measurement techniques for characterizing the behavior of organic chemicals in soils water, air, systems and monitoring of chemicals in the environment; (2) improved predictability of chemical release from soils to water and ecological receptors; (3) a more thorough understanding of microbial community population, structure, diversity, and transfer of genetic information as it applies to contaminant degradation behavior in the field; (4) initial assessment of the persistence, occurrence and mobility of antibiotics from animal production units and the potential for impacting microbial communities; (5) evaluate the environmental fate of new pesticides; and (5) recommendations for pesticide use, application methods, and region-, pesticide-, and crop-specific irrigation practices to minimize environmental contamination without compromising efficacy (e.g., reduced-fumigant application methods; BMP in cranberry productions ).

Outcomes or Projected Impacts

Milestones

(0):0

Projected Participation

View Appendix E: Participation

Outreach Plan

Organization/Governance

Literature Cited

The regional research technical committee consists of members who represent AES, USDA-ARS, and other research units. All voting members of the committee are eligible for office. A chairman and secretary are elected each year. The chairperson will coordinate the regional research activities, arrange annual meetings, and prepare annual reports in consultation with the committee members, the administrative advisor, and the CSRS representative. The secretary will record and distribute the minutes of the annual meeting, perform duties of the chairperson in case of absence, and be promoted to chairperson at the conclusion of the one-year of office. The chairperson and secretary, in conjunction with the site host comprise the executive committee. Ad hoc subcommittees are formed when needed to deal with special charges.

Attachments

Land Grant Participating States/Institutions

AL, AZ, CA, CT, DE, FL, GA, HI, IA, ID, IN, MI, MN, OK, SD, TN

Non Land Grant Participating States/Institutions

University of Illinois at Urbana-Champaign, USDA-ARS/Maryland, USDA-ARS/Minnesota, USDA/ARS-California