Brief Summary of Minutes of Annual Meeting

The 2009 meeting of W-1082, 'Evaluating the Physical and Biological Availability of Pesticides and Pharmaceuticals in Agricultural Contexts' was held on November 12 and 13, 2009 in Chandler, AZ hosted by Clinton Williams. Lee Sommers (Administrative Advisor) was available by conference call. The meeting included presentations of research reports by all participants. Jack Watson served as Secretary and Clinton Williams served as Chair of the committee. Joe Pignatello was elected (in absentia) to serve as Secretary for the next two years. It was determined by consensus of the attending members that next year's meeting would be hosted by Chitteranjan Ray at the University of Hawaii - Manoa Campus in January 2011.

Objective 1: To identify and quantify fundamental chemical, physical, and biological processes relevant to agricultural pesticides and pharmaceuticals in the environment. Alabama: Stabilized iron oxide nanoparticles have potential for in-situ environmental remediation. However, little is known regarding the impact of these nanoparticles on soil microorganisms. This study aimed to investigate the effects of Fe3O4 nanoparticles on four pure cultures of bacteria, i.e., Escherichia coli, Pseudomonas aeruginosa, Bacillus subtilis, and Enterococcus faecalis. The effect of commercial and lab-prepared Fe3O4 nanoparticles was examined through growth experiments and observation of cell-nanoparticle interactions. The results show that Fe3O4 nanoparticles at concentrations of 0.3, 0.6, and 1.0 g Fe/L were neither toxic nor inhibitory to the four organisms tested. In some cases, growth stimulation was observed. After the addition of culture to nanoparticle suspensions, there was a loss of particle stability manifested by the formation of large aggregates. Scanning electron microscopy was performed on the aggregates formed in E. coli culture to examine the cell-nanoparticle interactions. Nanoparticles were found to cover cell surfaces and bridge cells together in clusters, but no damage to cell integrity was observed. E. coli cells blanketed by nanoparticles retained the shape of healthy cells. Aggregates formed in the presence of bacteria consisted of nanoparticles and bacterial cells held in the nanoparticle matrix. The results suggest that stabilized nanoparticles may interact with bacterial surfaces without causing damage sufficient to inhibit cell growth. Arizona: Guayule is the only commercial source of domestic latex currently available in the US. Laboratory sorption experiments were conducted to determine the extent to which soil organic matter derived from guayule residues can affect the sorption of pendimethalin. Soils where guayule had been grown for 0 to 38 months were collected for sorption experiments from beneath actively growing plants. An additional treatment was collected prior to planting cotton in a field one year after the final harvest of guayule that had been grown for 36 months was also included. Continuous guayule cultivation resulted in a modest increase in soil organic carbon from 0.29% (±0.01%) to 0.76% (±0.03%) after 38 months of production. Pendimethalin sorption to the soil increased with increasing guayule organic deposition as measured by time under cultivation. Soils where guayule was grown for 38 months had a KOC 23 times greater than the control soil where guayule had not been grown (389,400 vs 16,900 L kg-1). However, in the treatment prior to planting cotton the combination of time and cultivation resulted in a reduction of KOC from 389,400 to 21,500 L kg-1. The use of pendimethalin in a guayule - cotton rotation requires sufficient time and primary tillage prior to planting cotton. In addition, the use of pendimethalin during re-growth of guayule from the stump following harvest may require higher application rates to control weeds. Adsorption of pendimethalin to soil using batch equilibrium indicated that soil beneath actively growing guayule has a higher sorption capacity for pendimethalin than soil without guayule. California-Berkeley: Investigating a simplified model of the acid-base chemistry of humic substances. Tetracycline and ciprofloxacin, two widely-used, environmentally-important antibiotics, are either cations or zwitterions over the range of pH typical of soils and receiving waters, implying a significant potential for adsorption by humic substances, which are anions in the same pH range. Recent studies of antibiotic adsorption by humic substances (see, e.g., our 2007 progress report) have confirmed this possibility, showing that humic substances may play an important role in controlling the fate of these and other cationic antibiotics in soil and aquatic environments. The available data also indicate that the affinity of humic substances for cationic or zwitterionic antibiotics is pH-dependent as a result of the variable charge of the adsorptive antibiotic and the humic adsorbent. Chemical modeling of this pH-dependent adsorption thus requires a suitable characterization of the acid-base chemistry of humic substances, an ongoing challenge in current research because of the complexity of these organic materials. We developed a model with three proton affinity classes to describe the acid-base chemistry of representative HS samples from both terrestrial and aquatic sources. The three pre-designated pKa values in our model, 3, 6, and 8, reflected proton dissociation constants inferred from recent comprehensive examinations of the acid-base chemistry of humic and fulvic acids. Our model was optimized on new blank-corrected base titration data that were properly renormalized, with model validation then achieved through comparing the optimized relative content of each affinity class with an independent quantitation of the acidic functional groups in the HS samples. UC-Riverside: Chiral pesticides currently constitute about 25% of all pesticides used, and this ratio is increasing as more complex structures are introduced. Despite the great public concerns associated with the use of pesticides, the environmental significance of chirality in currently used insecticides is poorly understood. Our research activities in 2009 on this topic include evaluation of chiral coversion induced by alcohols. Epimerization of Cypermethrin Stereoisomers in Alcohols. Isomerization induced by light, heat and organic solvents has been shown to occur for some pyrethroid insecticides. Alcohols are popular solvents that are used in sample extraction, storage and analysis. Thus, alcohol-induced epimerization may contribute to the incorrect interpretation of results from enantioselective chemical analysis and bioassay of pyrethroids like cypermethrin. In this study, we investigated the relationship between the rate of epimerization of cypermethrin stereoisomers: 1R-cis-±R and 1R-trans-±R and short-chain alkyl alcohol properties. In the present study, complete epimerization of 1R-cis-±R produced an almost equal fraction of 1R-cis-±S and that of 1R-trans-±R yielded 1R-trans-±S. For both stereoisomers, epimerization was most rapid in ethanol. The same stereoisomers underwent relatively rapid epimerization in methanol, n-propanol, 2-methyl-1-propanol and n-butanol, but were stable in 2-butanol, suggesting that secondary alcohols have reduced reactivity, likely due to steric hindrance. We further evaluated epimerization of 1R-cis-±R and 1R-trans-±R stereoisomers of cypermethrin as a function of water content in methanol. The presence of water in methanol generally increased the epimerization rate. For 1R-cis-±R, epimerization was most rapid at a water content of d 2%, while for 1R-trans-±R, epimerization was most rapid at 10% water content. Results from this study clearly show that contact with commonly used primary alcohols may result in rapid abiotic epimerization, underscoring the importance to consider configurational stability in ensuring the analytical integrity and correct interpretation of bioassay data for stereoisomers of cypermethrin and similar pyrethroids. Bioavailability of hydrophobic contaminants: Hydrophobic contaminants such as synthetic pyrethroids and PAHs are extremely hydrophobic and their biological effects are governed by their bioavailability. In 2009 we expanded our research on the phase distribution and bioavailability of pyrethroids and PAHs in soil and sediment. The following are brief summaries of two representative publications on this subject. Simultaneous determination of free and total concentrations. Hydrophobic contaminants partition between water and sorbent phases such as dissolved organic matter (DOM) in environmental matrices. Consideration of bioavailability increasingly requires the measurement of freely dissolved concentration (Cfree) in addition to the total chemical concentration (Ctotal). However, current practices require the use of separate methods and samples to derive Cfree and Ctotal, and no method affords simultaneous measurement of both concentrations. We employed a method by coupling solid phase microextraction (SPME) with the use of an isotope labeled internal standard and gas chromatography  mass spectrometer (GC-MS) for detection. The method was demonstrated using 8 pyrethroids as model compounds and 13C-cis-permethrin as the labeled internal standard. Analysis of 4 spiked sediment porewater and 4 field-contaminated samples showed that Ctotal obtained by this method was in close agreement with the spiked concentrations or the total concentrations measured after whole-sample solvent extraction, while Cfree was only a small fraction of Ctotal, suggesting pronounced association of these compounds with DOM. The method displayed good reproducibility with average relative standard deviation < 20%, and high sensitivity with method detection limits in the range of 1-5 ng L-1. The method uses a small sample volume (< 20 mL, as opposed to 1 L for conventional analysis), and is solvent-less and fast. The concurrent measurements also allow for estimation of KDOC, a key parameter that is difficult to derive otherwise. The simultaneous determination of Cfree and Ctotal provides information for better relating chemical concentrations with potential ecotoxicological effects. Colorado: Some chemicals have the apparent ability to disrupt normal endocrine system functions after exposure to concentrations so small that they are difficult to detect in the environment. The objectives of this study were to investigate the presence of steroid sex hormones in northern Colorados Cache la Poudre River, to determine the potential for steroid sex hormone biodegradation and photodegradation under natural conditions, and to characterize the mobility of selected steroid sex hormones in agricultural fields using a rainfall simulator. The study determined that steroid sex hormones are present in the Cache la Poudre River, at concentrations ranging from 0.6 ng L1 (epitestosterone) to 22.6 ng L1 (estrone). The study also determined that testosterone, progesterone, and 17²-estradiol can be degraded by manure-borne bacteria, and that testosterone degradation is faster under aerobic conditions and at higher temperatures (i.e., 37°C vs. 22°C), but little affected by changes in pH (from 6 to 7.5) or glucose amendments. In ultraviolet light » > 340 nm, the study observed direct photodegradation of testosterone and progesterone, and indirect photodegradation of testosterone and 17²-estradiol in the presence of Elliot soil humic acid. On the other hand, in ultraviolet light » > 310 nm, direct photodegradation of androstenedione was substantially faster than direct photodegradation of testosterone in ultraviolet light » > 310 nm, and no indirect photodegradation observed. The study detected and identified three testosterone biodegradation products (dehydrotestosterone, androstenedione, and androstadienedione), and detected several products of testosterone and androstenedione photodegradation which appear to retain their steroid structure, and possibly their endocrine disrupting potential. Finally, the study generally observed that androgen runoff concentrations follow runoff rates and decrease after successive rainfall events, while runoff concentrations of other analytes (e.g., estrone) peak after the maximum runoff rate and first rainfall event. Sample and data analysis from the study are continuing, and comprehensive finding and recommendations are expected after the date of this report. Hawaii: Crop losses, impact on native vegetative populations - causing changes in ecosystems, have been correlated to increases in invasive snail populations. These in turn have had major economic impact on developing countries, raised environmental concerns in developed countries, and impacted crop production/yields worldwide. Invasive tropical snails are carriers of disease, which greatly impact human health in under-developed tropical countries. Their effect on human health impacts productivity, self-sufficiency and economic development. Iowa: This project deals with the fate of hormones in soils where they are added by land application of cattle manure. Our long-term goal is to improve risk assessment of hormones in the environment, especially those derived from concentrated animal feeding operations (CAFOs). We are determining how colloidal materials in manure and soils retain the two hormones estradiol and estrone. We found that WDCs had markedly higher organic carbon contents than their parent soil materials and were dominated by smectite in the mineral fraction for these three soils. The organic carbon contents were strongly correlated with adsorption intensity for these three Iowa soils and their WDCs, as evidenced by similar Koc values. But not all soil organic matter was the same with respect to adsorption. There were differences in log Koc values among the two alluvial soils and one till-derived soil. Moreover, water-dispersible colloids had higher Koc values than their parent soil materials. This was particularly true of the clay-rich that had also previously received biosolids amendments. In the remaining project period, we will explore the conditions under which the retention of these hormones by colloidal components either enhances or retards their movement in the soil and over the soil. These experiments are crucial in the development, parameterization, calibration, and validation of hormone transport models that will be used to guide both management and regulation of land-applied manure. Michigan: Clay minerals may be an important unrecognized sorptive phase for dioxins in soils and clay deposits. Smectites, especially Cs-saponite, effectively adsorbed dibenzo-p-dioxin from water, reaching 0.8 % (wt/wt). Adsorption was promoted by exchangeable cations with low hydration energies, and negative charge in the smectite arising from the tetrahedral siloxane sheets. X-ray diffraction measurements revealed that as dioxin loading increased to e 8,000 mg/kg the clay basal spacing increased abruptly from 12.3 to 15.2 angstrom demonstrating dioxin intercalation. The 12.3-angstrom spacing provides an interlayer distance that closely matches the molecular thickness of dioxin. In this configuration dioxin is essentially dehydrated as it interacts with the opposing hydrophobic siloxane sheets and with co-planar Cs+ via one of the dioxin ring oxygens. Ab initio calculations suggest that geometrical structures form at higher loadings in which intercalated dioxin molecules adopt a butterfly geometry sandwiched between dehydrated interlayer Cs+ and the siloxane surface, consistent with the 15.2 angstrom spacing, wherein Cs+ interacts with dioxin ring oxygens and benzene ring pi-electrons. Fourier transformation infrared measurements confirm that adsorbed dioxin is present in orientations that are not parallel with the interlayer planar siloxane surfaces of smectite. Clay minerals also strongly sorb many pharmaceuticals. Lincomycin, an antibiotic widely administered as a veterinary medicine, is frequently detected in water. Little is known about the soil-water distribution of lincomycin despite the fact that this is a major determinant of its environmental fate and potential for exposure. Cation exchange was the primary mechanism responsible for lincomycin sorption by soil clay minerals. This was evidenced by pH-dependent sorption, and competition with inorganic cations for sorptive sites. As solution pH increased, lincomycin sorption decreased. The extent of reduction was consistent with the decrease in cationic lincomycin species in solution. The presence of Ca2+ in solution diminished lincomycin sorption. Clay interlayer hydration status strongly influenced lincomycin adsorption. Smectites with the charge deficit from isomorphic substitution in tetrahedral layers (i.e. saponite) manifest a less hydrated interlayer environment resulting in greater sorption than that by octahedrally substituted clays (i.e. montmorillonite). Strongly hydrated exchangeable cations resulted in a more hydrated clay interlayer environment reducing sorption in the order of Ca- < K- < Cs-smectite. X-ray diffraction revealed that lincomycin was intercalated in smectite clay interlayers. Sorption capacity was limited by clay surface area rather than by cation exchange capacity. Smectite interlayer hydration was shown to be a major, yet previously unrecognized, factor influencing the cation exchange process of lincomycin on aluminosilicate mineral surfaces. USDA-ARS, Minneapolis, MN: An enrichment culture approach was used to isolate a pure culture of the yeast Lipomyces kononenkoae, which had the ability to grow on the herbicide picloram. The yeast rapidly and completely degraded 50 µg/mL picloram by 48 hr of growth. While L. kononenkoae was found to use both N atoms of picloram as a sole nitrogen source for growth, it failed to mineralize the herbicide or use it as a sole C source. Product analysis done using LC-ESI-MS indicated that biodegradation of picloram by L. kononenkoae proceeds via a didechlorinated, dihydroxylated pyridinecarboxylic acid derivative. Our results are consistent with the hypothesis that the majority of picloram degradation in the soil is likely due to microbial catabolic processes. USDA-ARS, Morris, MN: Information regarding the impact of varying soil, landscape, and climate conditions on the off-site transport of pesticides is critical to the development of improved pesticide management practices. We quantified the rate of S-metolachlor dissipation after fall and spring application in eroded and rehabilitated landforms in which topsoil was moved from the lower slope to the upper slope. Despite large differences in soil properties, including soil organic carbon contents that varied by up to a factor of 4, the rate of metolachlor dissipation from the top 1 m was essentially the same at all landscape positions. Most of the fall-applied metolachlor was depleted from the root zone during the winter (presumably by leaching and runoff), so that only 20% of the applied metolachlor remained in the top 1 m of the soil profile at the beginning of the growing season. S-metolachlor dissipated in the spring with a half-life of 24 to 29 d. Bromide and metolachlor were depleted from the root zone at nearly the same rate during most of the growing season, suggesting that metolachlor degradation and plant uptake acted together to result in a dissipation rate similar to that for a non-reactive tracer, which was primarily dissipated through plant uptake. In these trials, fall-applied metolachlor dissipated prior to spring planting to such an extent that it provided no control of annual grasses. The results of this research suggest that fall-applied metolachlor may not provide economic weed control and presents an increased risk of water contamination. Although landscape position and bulk soil movement within the landform had a large impact on soil properties, we observed no significant differences in metolachlor dissipation between different landscape positions and between eroded and rehabilitated landforms. Missouri: Vegetative buffer strips (VBS) are postulated to be one management tool that can reduce VA transport to surface water resources. The objectives of this study were to (1) investigate oxytetracycline (OTC) and sulfadimethoxine (SDT) sorption to agroforestry buffer, grass buffer, and cropland soils, (2) evaluate differences in VA sorption to soils collected from different vegetative managements and soil series, and (3) elucidate relationships between soil properties and VA sorption. Sorption/extraction isotherms for OTC were well-fitted by the Freundlich isotherm model (r2 > 0.86). Oxytetracycline was strongly adsorbed by all soils and the VA was not readily extractable. Oxytetracycline and SDT solid to solution partition coefficients (Kd) values are significantly greater for soils planted to VBS relative to grain crops. Significant differences in OTC and SDT Kd values were also noted among the soil series studied. Linear regression analyses indicate that clay content and pH were the most important soil properties controlling OTC and SDT adsorption, respectively. Greater clay content in the VBS is hypothesized to occur due to improved aggregation and stabilization of soil by permanent vegetation and the deposition of clay particles and clay aggregates as runoff waters pass through VBS. Lower soil pH in VBS is attributed to lack of liming VBS. Results from this study suggest that agroforestry and grass buffer strips may effectively mitigate antibiotic loss from agroecosystems, in part, due to enhanced antibiotic sorption properties. Pennsylvannia: Sample cleanup and concentration procedures have been worked out for soil samples such that we have confidence in results. Maintenance of a unit hydraulic gradient in the soil columns has been an issue and recently solved with some modifications from earlier designs. Samples have been collected from a few locations in an effluent irrigated location to determine distribution of three estrogens by depth. One set of samples have been analyzed for estrone, indicating that for the sample site, deeper sampling depths than those originally expected are needed. We have obtained data comparing the degree of sorption of estrone to soil organic carbon at relatively high concentrations (from approximately 5% to 50% of the estrone aqueous solubility concentration), using radiolabeled techniques as well as non-radiolabeled techniques using batch isotherms and extraction of soil sorbed estrone. The collaboration with USDA-ARS in AZ has proven quite beneficial, as the equipment available for research has yielded dependable results. Based on conversation with the extension program leader for the environment, the college strategic plan includes an emphasis by both the water quality and crop nutrient management groups on emerging contaminants. This research work has been cited internally as support for the educational programs being developed. So the impact has not yet reached citizens directly, but will during the next 5 year plan of work, because of the internal impact related to extension program planning. South Dakota: This study investigates the effects of two universally administered animal feed additives, tylosin and chlorotetracycline (CTC), during batch anaerobic swine manure digestion. Both compounds are poorly absorbed within the swine intestines and consequently, these compounds and bioactive metabolites are excreted. The breakdown of insoluble organic matter through anaerobic hydrolysis reactions were faster for manure containing CTC compared with tylosin or no-antimicrobial treatments, however volatile fatty acid (VFA) accumulation, including acetate, butyrate, and propionate, was significantly greater for CTC compared to the tylosin and no-antimicrobial control treatments. Aceticlastic methanogen abundance for CTC treatments (Methanosaetaceae and Methanosarcinaceae spp.) were less than no-antimicrobial control treatments, and methane and carbon dioxide generation rates were inhibited due to the presence of CTC. For tylosin, effects on manure degradation were limited, however their was a significant shift in the relative abundance of aceticlastic methanogens Methanosaetaceae and Methanosarcinaceae spp. compared to no-antimicrobial control treatments, suggesting that other C-1 VFA compounds in addition to acetate appear to be effectively utilized during methanogenesis in the presence of tylosin. Life cycle assessment of tylosin and chlortetracycline antimicrobial use at swine production facilities - This study investigates the environmental effects associated with tylosin and chlortetracycline (CTC) antimicrobial sub-theraputic use within Midwestern US swine production facilities following life cycle assessment (LCA) methodology. Environmental LCA-associated impacts were modeled using SimaPro and assessed using EcoIndicator 99 for antimicrobial manufacturing, feed blending and transport, metabolic and manure emissions, and facility operations for starter, grower, and finishing swine operations. LCA results suggest current high energy demands associated with manufacturing fermentation processes and large transport distances to producers of CTC and tylosin increased disability adjusted life year (DALY) climate change impacts compared to no antimicrobial use. Feeding CTC resulted in several local positive changes including 20% increase in feed utilization and reduced manure greenhouse gas emissions. However, these positive changes in the local environment did not offset negative global impacts associated with material manufacturing and transport. Using renewable energy sources for production and transport would result in net environmental enhancement. Wisconsin: Assessing occurrence, persistence and biological effects of hormones released from livestock waste. The overall goal is to determine the presence, persistence and biological effects of natural and synthetic hormones that may be released into the environment from concentrated animal feed operations (CAFOs), and evaluate the effects of different animal waste disposal practices on the fate and activity of these compounds. This research will help to evaluate whether CAFO waste is an important source of endocrine disrupting chemicals in the environment. Seven hormones were identified and quantified using HPLC-MS/MS in the snow-melt grab samples. These include: estradiol, a-zearalanol, zearalenone, 4-androstene-3,17-dione, 17b-nortestosterone, progesterone, and 17,20-dihydroxyprogesterone. Levels of most hormones were <100 ng/L, though concentrations of the most prevalent hormones (progesterone, 17,20-dihydroxy-progesteone, and zearalenone) ranged up to 350 ng/L. Estrogenic activity from the snow melt samples were also determined using the E-screen bioassay. In this assay, the only target compounds that should elicit a response would be estriol, estradiol, estrone and the zearanols. In general, trends in the E-screen bioassay were consistent with the chemical profiles of the samples. Fathead Minnow Exposures - Three percent CAFO effluent (from a steer facility) had no effect on the number of eggs produced by fathead minnows during a three week exposure. In addition, the levels of vitellogenin expression in the exposed males were similar to their respective controls. The levels of hormones may have been too low to cause an effect due to the dilution of effluent (necessary to prevent ammonia toxicity to the fish) or rapid degradation of hormones associated with the liquid manure. We completed a study using Computer Assisted Sperm Analysis (CASA) to investigate the acute effects of various progestins on sperm motility in fathead minnows. Semen samples were exposed short-term in vitro to various doses of progesterone, 17a,20b-P, or melengestrol acetate (MA). The sperm were activated, video recorded, and analyzed for the following parameters using CASA: percent motility, curvilinear velocity, velocity average path, straight line velocity, and percent linearity. Preliminarily, short-term progesterone exposure had a slight, but significant effect on fathead minnow sperm motility. Objective 2: Integrate chemical and biological process information for use in models applicable across different spatial and temporal scales. USDA-ARS, Morris, MN: Metolachlor transport in eroded and rehabilitated prairie landforms - Information regarding the impact of varying soil, landscape, and climate conditions on the off-site transport of pesticides is critical to the development of improved pesticide management practices. We quantified the rate of S-metolachlor dissipation after fall and spring application in eroded and rehabilitated landforms in which topsoil was moved from the lower slope to the upper slope. Despite large differences in soil properties, including soil organic carbon contents that varied by up to a factor of 4, the rate of metolachlor dissipation from the top 1 m was essentially the same at all landscape positions. Most of the fall-applied metolachlor was depleted from the root zone during the winter (presumably by leaching and runoff), so that only 20% of the applied metolachlor remained in the top 1 m of the soil profile at the beginning of the growing season. S-metolachlor dissipated in the spring with a half-life of 24 to 29 d. Bromide and metolachlor were depleted from the root zone at nearly the same rate during most of the growing season, suggesting that metolachlor degradation and plant uptake acted together to result in a dissipation rate similar to that for a non-reactive tracer, which was primarily dissipated through plant uptake. In these trials, fall-applied metolachlor dissipated prior to spring planting to such an extent that it provided no control of annual grasses. The results of this research suggest that fall-applied metolachlor may not provide economic weed control and presents an increased risk of water contamination. Although landscape position and bulk soil movement within the landform had a large impact on soil properties, we observed no significant differences in metolachlor dissipation between different landscape positions and between eroded and rehabilitated landforms. Objective 3: Provide stakeholders with tools for developing strategies to ensure sustainable agriculture and to protect natural resource systems. California-Riverside: Oxidative Removal of Bisphenol A (BPA) by Manganese Dioxide - Bisphenol A (BPA) is a ubiquitous environmental contaminant with endocrine disruption potential. In this study, exploiting the outstanding oxidative capacity of manganese dioxide (´-MnO2), we explored for the first time the efficacy and mechanisms of BPA removal by MnO2. In aqueous solutions, MnO2 displayed an extremely efficient capacity to remove BPA. Nearly all BPA (> 99%) was eliminated in 6 min in a pH 4.5 solution initially containing 800 ¼M MnO2 and 4.4 ¼M BPA. While humic acid showed negligible inhibition on BPA removal, co-existing metal ions such as Mn2+, Ca2+, Mg2+, and Fe3+ displayed suppressive effects and the inhibitive capacity followed the order of Mn2+ > Ca2+ > Mg2+ H Fe3+. A total of 11 products or intermediates were indentified and a detailed reaction scheme was suggested. The products could be ascribed to a suite of reactions of radical coupling, fragmentation, substitution, and elimination, triggered by the BPA radical formed through electron transfers to MnO2. The exceptional efficiency of MnO2 in removing BPA represents a perspective use of MnO2 to treat waters containing phenolic compounds, and also suggests a potentially important role of oxide-facilitated abiotic transformations in BPA attenuation in natural soil and sediment environments. Use of Constructed Wetlands to Remove Pesticides in Tailwaters. Pollutants in agricultural irrigation return flow (tailwater) constitute a significant non-point source of pollution in intensive agricultural regions such as the Central Valley of California. Constructed wetlands (CWs) represent a feasible mitigation option to remove pollutants including pesticides in the tailwater. In this study, we evaluated two CWs in the Central Valley for their performance in removing pyrethroid and organophosphate insecticides under field-scale production conditions. Both CWs were found to be highly effective in reducing pyrethroid concentrations in the tailwater, with season-average concentration reductions ranging from 52 to 94%. The wetlands also reduced the flow volume by 68-87%, through percolation and evapotranspiration. When both concentration and volume reductions were considered, the season-average removal of pyrethroids ranged from 95 to 100%. The primary mechanism for pyrethroid removal was through sedimentation of pesticide-laden particles, which was influenced by hydraulic residence time and vegetation density. The season-average removal of chlorpyrifos ranged 52-61%. The wetlands, however, were less effective at removing diazinon, likely due to its limited sorption to sediment particles. Analysis of pesticide partitioning showed that pyrethroids were enriched on suspended particles. Mass balance calculation of suspended solids suggests that the sediment basin served as the primary sink for pesticides on a mass basis, and the CWs were able to remove fine particles enriched with pesticides. Results from this study show that flow-through CWs, when properly designed, are an effective practice for mitigating hydrophobic pesticides in the irrigation tailwater.

Wang, L.M., S.S. Zhou, K.D. Lin, M.R. Zhao, J. Gan, and W.P. Liu. 2009. Enantioselective estrogenicity of o,p2-dichlorodiphenyltrichloroethane in the MCF-7 human breast carcinoma cell line. Environmental Toxicology & Chemistry 28: 1-8. Hunter, W., Y. Yang, F. Reichenberg, P. Mayer, and J. Gan. 2009. Measuring pyrethroids in sediment porewater using matrix-solid phase microextraction. Environmental Toxicology & Chemistry 28: 36-43. Yang, Y., W. Hunter, S. Tao, and J. Gan. 2009. Effects of black carbon on pyrethroid bioavailability in sediments. Journal of Agricultural & Food Chemistry 57: 232-238. Wang, H.Z., J. Gan, J.B. Zhang, J.M. Xu, S.R. Yates, J.J. Wu, and Q.F. Ye. 2009. Kinetics 14C-metsulfuron-methyl residues in paddy soils under different moisture conditions. Journal of Environmental Quality 38: 164-170. Zhao, M.R., Y. Zhang, C. Wang, Z.W. Fu, W.P. Liu, and J. Gan. 2009. Induction of macrophage apoptosis by an organochlorine insecticide acetofenate. Chemical Research in Toxicology 22: 504-510. Lin, K.D., D. Haver, L. Oki, and J. Gan. 2009. Persistence and sorption of fipronil degradates in urban stream sediments. Environmental Toxicology & Chemistry 28: 1462-1468. Cáceres-Jensen, L. J. Gan, M. Báez, R. Fuentes, and M. Escudey. 2009. Adsorption of glyphosate on variable-charge Chilean soils. Journal of Environmental Quality 38: 1449-1457. Yang, Y., W. Hunter, S. Tao, and J. Gan. 2009. Microbial availability of different forms of phenanthrene in soils. Environmental Science & Technology 43: 1852-1857. Mangiafico, S.S., J. Newman, D.J. Merhaut, J. Gan, B. Faber, L. Wu. 2009. Nutrients and pesticides in stormwater runoff and soil water in production nurseries and citrus and avocado groves in California. HortTechnology 19: 360-367. Budd, R., A. OGeen, K. Goh, S. Bondarenko, and J. Gan. 2009. Efficacy of constructed wetlands in pesticide removal from tailwaters in the Central Valley, California. 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