Brief Summary of Minutes of Annual Meeting

The 2006 meeting of W-1082 Evaluating the Physical and Biological Availability of Pesticides and Pharmaceuticals in Agricultural Contexts was held on January 5 and 6, 2006 at the University of Tennessee in Knoxville, TN. Mark Radosevich hosted the meeting. Lee Sommers (Administrative Advisor) provided an overview of the budget outlook for the coming year. He noted that the Western directors are emphasizing accountability for multi-state research projects, requiring reports showing the impact of each committee. Dr. Sommers congratulated the group on a successful proposal. Members discussed progress on the outputs and milestones specified in the proposal and approaches to increase the impact of the committee. The meeting included presentations of research reports by all participants. Mark Radosevich was elected chair for the next W-1082 meeting, and Clinton Williams was elected as secretary. The next meeting will be hosted by Chitaranjan Ray in Hawaii on January 4-5, 2007.

Objective 1. to identify and quantify fundamental chemical, physical, and biological processes relevant to agricultural pesticides and pharmaceuticals in the environment A. Sorption of Agrochemicals - Sorption-desorption is arguably the most important process affecting the transport of pesticides through soil since it controls the amount of pesticide available for transport. Sorption is usually characterized by determining batch sorption coefficients, which are then used in transport models to predict movement from the soil surface through the subsoils. Variability in subsurface soil properties can significantly affect pesticide transport. Research conducted by USDA-ARS scientists in Morris and St. Paul, MN characterized the sorption-desorption of the insecticide imidicloprid and three of its metabolites (imidacloprid-urea, imidacloprid-guanidine, and imidacloprid-guanidine-olefin) as a function of changing soil properties with depth in two soils. Overall, sorption of imidacloprid and all metabolites increased with increasing organic carbon, clay content, and cation exchange capacity. In each of the four cores, measured sorption coefficients (Kf) and coefficients normalized to the organic carbon content (Koc) or clay content (Kcm) varied over an order of magnitude. If OC contents of the subsoils and the surface Koc value were used to predict subsurface imidacloprid Kf values, predicted subsurface Kf values were 5 to 420% of actual measured values. Similar results were observed for each metabolite. Using multiple linear regression (OC, clay, and pH) of the pooled data did not significantly improve Kf predictions. These data illustrate the importance of evaluation of the sorption data used to predict potential mobility; mobility could be either over- or under-predicted depending on the sorption coefficients used. Desorption hysteresis further complicates prediction of imidacloprid mobility. Understanding the variability of soil properties and processes as a function of soil depth is necessary for accurate prediction of pesticide dissipation. As part of a research program to more fully characterize the sorption of organic compounds to soil organic matter (SOM) substances, Connecticut researchers have investigated history-dependent sorption behavior, in particular hysteresis and the conditioning effect. Hysteresis is observed when the sorption and desorption branches of the isotherm do not coincide. In the absence of artifacts it is called true hysteresis, or irreversible sorption. The term conditioning effect refers to the result of enhanced sorption of a test compound following the sorption (and then removal) of a conditioning agent, which could be the same or a different compound. Our working hypothesis is that these two behaviors are related mechanistically and are due to pore expansion and pore creation processes in the solid that are irreversible on the timescale of molecular diffusion in the solid. Such a mechanism is well established for glassy organic polymers. Results indicated that relaxation of the conditioning effect in the SOM solids depended on annealing temperature and, at a given temperature, followed a double additive exponential rate law with a non-zero constant term descriptive of the final state that depends inversely on temperature. By extrapolation, it could be predicted that the conditioning effect may never completely relax at environmentally relevant temperatures. The results provide compelling evidence for the glassy, non-equilibrium nature of natural organic matter solids and for irreversible structural expansion as a cause of irreversible sorption phenomena, such as hysteresis and conditioning. A portion of tylosin, a macrolide antimicrobial chemical used in swine, cattle, and poultry production, is excreted unchanged in manure. The sorption characteristics of tylosin to soil and manure will influence its fate in the environment. Researchers at South Dakota State University assessed sorption and desorption of tylosin in three silty clay loam soils of South Dakota and compared soil sorption data to sand and manure. The silty clay loam soils, from a toposequence in eastern South Dakota, standardized sand samples, and swine manure were used in 24-hr batch sorption studies with tylosin concentrations ranging from 25 to 232 ¼mole L-1. Desorption from soil was conducted over a 4-d period. Partition coefficients, based on the Freudlich isotherm (Kf) or Kd values, were calculated. Kf values for the silty clay loams were similar, not influenced by landscape position, and averaged 1350 with isotherm slopes ranging from 0.85 to 0.93. Kf values for sand were dependent on solution/sand ratios and pH, ranging from 1.4 to 25.1. Kd values of manure were dependent on the solution type and ranged from 840 L kg-1 with urine to about 175 L kg-1 when sorbed from water. Desorption of tylosin from each soil over the 4-d period was <0.2% of the amount added. The soils high Kf values and low desorption amounts suggest that once tylosin is in these soils, leaching to lower depths may not occur. However, this does not preclude runoff with soil eroded particles. If tylosin reaches a sand aquifer, through bypass flow or other mechanism(s), movement in the aquifer most likely would occur. In experiments conducted by University of California, Riverside scientists, in situ diffuse reflectance spectroscopy (DRIFT) was used to investigate sorption and desorption processes for water vapor on both specimen clay minerals and soils. Results indicated that condensation of vapor phase chemical to a liquid occurs spontaneously within pores of nanoporous dimension because of free energy differences between the bulk and sorbed states. As the liquid advances into the porous network, sorbed chemical in the vapor state must also be present at the liquid meniscus. Intermolecular forces that facilitate capillary flow of liquids both into and out of pores are not effective for molecules in the vapor state which are thus retained for extended periods of time within the pore system. Subsequent condensation events, whether of pollutant chemical or water, provide additional forces that can drive those vapor state molecules further into pore regions where molecular displacement is even more difficult. Scientists at Auburn and the University of Arkansas investigated the role of a wheat-residue-derived char in nutritional stimulation and adsorptive inhibition on biodegradation of benzonitrile in a soil. The biodegradation was measured at 78 mg/l of benzonitrile, an initial concentration much higher than the half-saturation constant of the degrading organism (~18 mg/l). The degradation was much faster in the extract of char-amended soil (CAS) than in those of soil and washed-char-amended soil (WCAS). The degradation was also faster in CAS slurry than in slurries of soil and WCAS until ~88% of benzonitrile degraded in char-containing slurries, where the aqueous-phase concentration was ~0.25 mg/l. Cell density was higher in extracts and slurries in the presence of the char nutrients than in the absence of them. Analysis of nutrient elements in extracts, along with measuring degradation in soil extract with nutrient supplements and subsequent stepwise multiple-regression, suggested that the char nutrients stimulated cell growth and degradation of benzonitrile, for which P was primarily responsible. Further degradation of benzonitrile beyond 88% in the presence of char was slow, suggestive of the adsorptive inhibition. The biodegradation of benzonitrile in CAS thus occurred through a fast-to-slow process, the former step being due primarily to the stimulation by soluble P of char and the latter phase to the adsorptive inhibition. B. Bioavailability of Agrochemicals - Scientists at the University of California, Riverside have conducted a series of studies to gain a better understanding of the interactions of pyrethroid phase distribution and their bioavailability to aquatic organisms. Contamination of surface streams by synthetic pyrethroids appears to be an emerging water quality issue in California and likely in other regions. Pyrethroid products are in widespread use in both urban and agricultural environments. Although pyrethroids have high aquatic toxicity, their strong adsorption may significantly affect their phase distribution and ultimately their actual toxicity. Characterization of pesticide bioavailability, particularly in aged soils, is of continued interest because this information is necessary for environmental risk assessment of pesticides. The objective of this study conducted by scientists at the USDA-ARS in St. Paul, MN was to correlate simazine (a triazine herbicide) residue bioavailability in aged soils, as determined by solvent extraction methods, to simazine mineralization by an simazine-degrading bacterium. We identified a 0.01 M CaCl2/methanol solvent extraction procedure that can characterize simazine bioavailability in dissimilar aged soils, which in turn may be useful to determine bioavailability of other compounds in soils, especially other triazine herbicides. Scientists now a relatively easy and inexpensive technique to determine the amounts of one class of pesticides, triazines, available for transport, plant uptake, and microbial degradation, particularly in aged soils, information needed for predicting environmental fate and environmental risk assessment. The impact of genetically modified plants containing Bacillus thuringiensis (Bt) toxin on soil processes has recently started to receive attention by scientists. Researchers at the University of Minnesota and the USDA-ARS in St. Paul, MN produced the insecticidal protein, Cry1Ac toxin, to determine the its effect on soil process affecting the herbicide glyphosate in two different soils. Glyphosate is an effective non-residual herbicide used to control a wide range of annual and perennial weeds. The addition of 0.25 to 1.0 µg/g soil of purified insecticidal protein did not significantly affect glyphosate bioavailability, that is degradation or binding, in either a sandy loam or a sandy soil. In contrast,we found that bioavailable glyphosate decreased over the 28-day incubation period in both soils. Our findings suggest that the reduction in the bioavailabily of glyphosate was not influenced by the presence of insecticidal protein, but rather the results of aging or binding processes. The influence of crop residue derived char on sorption, desorption, and bioavailability of atrazine was evaluated by scientists at Auburn University and the University of Arkansas using two soils (Hartsells and Grady) in the presence and absence of a wheat char. Both char amended soils produced similar isotherms indicating that the presence of small amount of char in soils dominates the overall sorption processes. The amount of atrazine sorbed by char was 800  3800 times more than the soils. With char amendment, both soils exhibited reduced hysteresis. Pseudomonas sp. strain ADP, capable of mineralizing atrazine, was used to evaluate bioavailability of atrazine. The presence of char in the system reduced both rate and extent of atrazine mineralization, which may be attributed to increased sorption of atrazine in char-containing systems. The results suggest that the presence of char in soils controls the sorption and desorption processes that influence the bioavailability of atrazine and may ultimately affect its environmental fate. A study, conducted by South Dakota State University researchers, determined uptake, translocation, and metabolism of ring-labeled-14C-2,4-D in soybean at the third trifoliate (V3) stage of growth. Plants were harvested and partitioned into four parts from 1 hr (HAT) to 10 d (DAT) after treatment. Thin layer chromatography techniques were used to determine if 14C remaining in the tissue was parent chemical or metabolite. 2,4-D uptake ranged from 39% at 1 HAT to 74% 6 DAT. By 10 DAT, 14C translocated to the youngest tissue (10%) and older tissue (8%). All 14C recovered from the treated leaf 1 HAT was parent 2,4-D, however, at 24 HAT and later, only about 30% of the 14C remained as 2,4-D whereas 70% of the 14C was observed as a more water soluble compound. Based on this research and evidence from the literature, the 2,4-D in the soybean plant was being conjugated into more water-soluble forms, either glucose or amino acid conjugates, or both. These reactions would decrease the 2,4-D concentration over time and are similar in the reduction of 2,4-D that is observed in field treated plants. These data would explain why, at the end of the season, no or very little 2,4-D was detected in stems or leaf tissue, although, injury symptoms were very evident. An acidic extraction, that may break the glucose or amino acid bond and change the metabolite back to parent acid, may yield a higher amount of 2,4-D in these plant tissues if further degradation does not occur. C. Transformation of Agrochemicals - Researchers at the USDA-ARS in Riverside, CA determined that chloropicrin undergoes an extremely rapid redox reaction in hydrogen sulfide solution. Transformation products indicated reductive dechlorination of chloropicrin by hydrogen sulfide species to produce dichloro- and chloronitromethane. The transformation of chloropicrin in hydrogen sulfide solution significantly increased with increasing pH, indicating that H2S is less reactive toward chloropicrin than HS is. Because of the relatively low smell threshold values and potential environmental persistence of organic sulfur products yielded by the reaction of 1,3-D and HS-, the effects of reduced sulfide species should be considered in the development of alternative fumigation practices, especially in the integrated application of sulfur-containing fertilizers. The interactions of stearic acid in a non-aqueous chemical environment with other non-aqueous chemical have not been adequately addressed. Solids researchers have proposed that stearic acid exist in a cubic phase, i.e. they self associate in a group of parallel aligned molecules. Researchers at the USDA-ARS in Beltsville, MD demonstrated that the same explanation holds for predicting the solubility of stearic acid in four of five structurally different solvents. Results suggest molecules that disrupt the stearic acid cubic array may also add to or detract from its desired physical properties in commercial products formulations. Scientists at the USDA-ARS in Riverside, CA and Morris, MN developed a chemical tarp approach, termed a reactive surface barrier (RSB), to reduce the emission of fumigant 1,3-dichloropropene (1,3-D) from the soil surface. The agrochemicals thiourea and allylthiourea were tested as active reagents for the construction of a RSB, where these soil amendments react with 1,3-D to form non-volatile isothiuronium ions at the soil surface, and thereby impede fumigant emission into the atmosphere. The present results clearly indicate that this chemical remediation technology has great potential to control the emissions of volatile halogenated organic contaminants and mitigate atmospheric pollution. The degradation kinetics of sulfadimethoxine, a widely used sulfonamide antibiotic, in manure under aerobic condition was investigated by USDA-ARS scientists in Riverside, CA. Based on the first-order kinetics and the assumption of the availability of sulfadimethoxine in manure for the degradation process, a new kinetic model was developed and was found to fit the degradation kinetics well. The degradation rate in sterilized manure was found to be much lower than in non-sterilized manure, indicating that microorganisms are responsible for a significant portion of degradation of this antibiotic in manure. Mixing highly contaminated manure with less contaminated, while keeping manure at high moisture and storing the manure in a moderately warm place under aerobic conditions, can greatly enhance the degradation of sulfadimethoxine in manure. This may be an effective approach for eliminating this contaminant from the environment. Spreading of contaminated manure into agricultural lands, as fertilizer is the major route through which veterinary antibiotics enter the environment. Researchers at the USDA-ARS in Riverside, CA investigated the degradation of manure-derived sulfadimethoxine, a widely used sulfonamide antibiotic, in manure-amended soil. Sulfadimethoxine degradation was effectively enhanced with the increasing moisture of amended soil. No adverse effect was observed with manure storage on the degradation of manure-derived sulfadimethoxine after application into soil. Tylosin (Tyl) and chlortetracycline (CTC) are antimicrobial chemicals used as growth promoters in cattle, swine, and poultry production and can be excreted as the parent compound. Landspreading manure can move these chemicals into soil and thereby change the soil microbial make up or degradative activity. The objective of this study, conducted by South Dakota State University scientists, was to determine if Tyl and CTC changed the growth or herbicide degrading activity of pure cultures of two bacteria, Pseudomonas ADP, an atrazine degrader, and Sphingobium herbicidovorans, a 2,4-D degrader. Research conducted by University of Georgia scientists has shown that 4-nonylphenol (4-NP) appears in biosolids at a wide concentration ranges, from several mg kg-1 to several thousands mg kg-1. A pilot scale laboratory-controlled composting experiment was conducted to investigate the effectiveness of 4-NP removal through mixing biosolids with wood shavings at different environmental conditions. The results from this investigation provided further evidence that 4-NP can be effectively degraded during composting. The success of this research will not only have significant economic impact on wastewater treatment plants in the United States and world-wide but also have tremendous environmental impact. The overall hypothesis of research conducted by University of Tennessee researchers is that the existing collection of bacteria does not adequately reflect all community member species involved in the breakdown of atrazine in soils and sediments. The focus of the first project year has been on the cultivation of atrazine degrading bacteria from field-incubated BioSep beads. To date, approximately 75 atrazine-degrading bacteria have been isolated from field sites in Ohio and Tennessee. Fifteen of these 75 isolates have been taxonomically identified and fall into one of three categories:1) closely related to known atrazine-degrading bacteria, 2) phylogenetically novel bacteria with few cultured relatives, and 3) strains that are not phylogenetically novel but not previously reported to degrade atrazine. Screening of these isolates for known atrazine catabolic genes is in progress. Several isolates exhibit strong atrazine degradation activity but apparently do not possess any of the known atrazine catabolic genes. These results suggest novel atrazine degradation genes are present in these bacteria. D. Improved Analysis of Agrochemicals - An analytical method for the determination of oxytetracycline, a member of tetracyclines, in steer manure was developed at the USDA-ARS in Riverside, CA. The method uses acidified methanol extraction and high performance liquid chromatography analysis. The obtained recoveries of oxytetracycline for all kinds of investigated manure and for the silt loam soil were more than (89.3±2.2)% and less than (102.5±5.0)%, demonstrating that the developed analytical method had a robust extraction ability for oxytetracycline from different manures and provided a reliable quantification of oxytetracycline content in different manures. E. Measurement of Agrochemical Fate and Toxicity - University of California, Riverside scientists resolved enantiomers of a number of synthetic pyrethroid and organophosphate insecticides on chiral selective columns, and evaluated occurrence of enantioselectivity in aquatic toxicity and biodegradation. Dramatic differences were observed between enantiomers in their acute toxicity to freshwater invertebrates Ceriodaphnia dubia and Daphnia magna, suggesting that the aquatic toxicity is mostly attributable to only a specific enantiomer in the racemate. Tennessee requires engineered wood (products that contain adhesive resins) waste to be placed in landfills rather than recycled. Regulators are concerned with potential adverse human and ecological health effects of resins that contain formaldehyde. Urea formaldehyde resin (UF) for example is used in medium density fiberboard (MDF) and plywood. In 2004-2005 a study was conducted at the University of Tennessee to 1) assess the fate of formaldehyde during the decomposition of land applied medium density fiberboard and 2) determine the effect of MDF application on the production of corn. The results showed that the added MDF residue was quickly degraded and formaldehyde emissions remained below detection throughout the growing season. Further, nitrogen from the MDF was mineralized, adding to the crop-available soil N. Although this did not result in statistically significant increases in corn yield, the plants in MDF-amended plots were obviously greener, more vigorous, and taller than control plots. The study was repeated in 2005 at several additional sites across Tennessee and soil samples were taken at greater depths to determine if any formaldehyde from the added MDFresidue leached below the rooting zone. The results showed that formaldehyde did not leach beneath the rooting zone and the N released from the added MDF increased crop biomass. The results show that land application of engineered wood waste such as MDF or particle board is safe and the formaldehyde is rapidly degraded, is beneficial to crop production, and offers a less expensive disposal alternative to landfills. These findings should significantly affect regulatory decisions regarding disposal of engineered wood waste, which will ultimately have a positive economic impact on industries that use these materials. Objective 2. Integrate chemical and biological process information for use in models applicable across different spatial and temporal scales. Fluoroquinolone antibiotics have become widespread in the environment because of their extensive use in human and veterinary medicine. To assess the risk from this contamination, a better understanding of their fate in soils and waters is required. This project conducted at the University of California, Berkeley quantified the fate and toxicological impact of an important antibiotic, ciproflaxin (Cipro), while exploring mechanisms through which it can be detoxified by natural organic matter (humus). Humus can play a crucial role in the environmental fate of pharmaceuticals by interacting with them. Molecular simulations of these interactions are useful as a guide to interpreting the results of both chemical and toxicological experiments. The research summarized here and reported in detail by Sutton et al. (2005) is the first rigorous computational exploration of the behavior of a model humic acid molecule under a variety of chemical conditions typical of soils and natural water. Rural domestic wells, particularly farmstead wells are not regulated. Researchers at the University of Hawaii use artificial neural networks (ANNs), an alternative modeling approach, to predict the contamination potential of domestic and farmstead wells using data from several states. In this year, they used data from selected large-scale studies of pesticide and nitrate assessment in North Carolina and Illinois. Human interaction, land use, and hydrogeologic data, in conjunction with the occurrence data were used for predictive simulations. Objective 3. To provide information required for field-scale recommendations for the management of agricultural pesticides and pharmaceuticals in the environment. Nursery and floriculture production is an important industry in California and many other states. However, commercial nurseries rely on heavy use of pesticides, fertilizers, and irrigation, and consequently, surface runoff is widespread at many nursery sites. Nursery runoffs commonly contain high levels of multiple pesticides, and discharge of nursery runoff contributes directly to water quality impairment of surface streams, especially in urban and suburban watersheds. In southern California, nursery runoff has been identified as an important source of pesticides detected in urban creeks and estuaries. In close collaboration with nursery growers in Orange County and Ventura County, University of California, Riverside scientists have carried out studies to understand the source, fate and distribution of pesticides in nursery runoff, and to develop best management practices (BMPs) to reduce pesticide load in the runoff. They have also worked closely with the State Water Resources Control Board, the Regional Boards, and California Department of Pesticide Regulation to extend the technology to nursery growers through many forms of public outreach and education activities, including training workshops for growers and pesticide applicators, and publication of fact sheets and newsletter articles. A GIS-based simulation tool was used by University of Hawaii researchers to calculate leaching characteristics of pesticides based upon soil physical/chemical properties, depth to water, recharge rate, and pesticide properties. The model is used to calculate leaching of existing and new chemicals coming to Hawaii on island-wide scale. Variability in soil organic carbon at various soil classification groups and the variabilities in half-life and organic carbon partition coefficients are taken into consideration while developing this GIS-based model. Soil database for all islands are now available and it was recently updated. Variation in recharge was also considered in the model. The model will be used by the Hawaii Department of Agriculture and pesticide registrants to evaluate relative attenuation of pesticides. If a new chemical appears to be significantly mobile compared to two reference chemicals (one that is frequently observed in drinking waters and the other has never been found so far), restrictive measures will be taken by the state for the registration of these compounds.The model was recently updated to ARC/GIS from Arc/View and all soil, pesticide, and recharge data were updated. The detailed evaluation 13 new chemicals have been completed where the registrants sought their use in Hawaii. Scientists at the USDA-ARS in Riverside, CA conducted a large-scale project highlighting a promising emission reduction methodology in the San Joaquin Valley near Buttonwillow, CA. Two fields were treated with 1,3-D and one of the fields received a surface water application (i.e., a water seal) at 11:00 am during the first few days after application. Emissions were determined using two independent measurement methods, aerodynamic and ambient methods. The data are currently being analyzed. Comparisons will be made between fields to determine if water seals are effective in reducing fumigant emissions. This research should lead to low-cost methods to reduce fumigant emission.