Brief Summary of Minutes of Annual Meeting

The 2008 meeting of W-1082 Evaluating the Physical and Biological Availability of Pesticides and Pharmaceuticals in Agricultural Contexts was held on January 8 and 9, 2008 in Riverside, CA hosted by Jay Gan. Lee Sommers (Administrative Advisor) was unable to attend. Nancy Cavallaro (USDA-CSREES) sent a Powerpoint presentation. The meeting included presentations of research reports by all participants. Jack Watson served as Secretary and Clinton Williams served as Chair of the committee. It was determined by consensus of the attending members that next years meeting would be hosted by Clinton Williams at USDA-Maricopa, Az in October 2009, for the development of the new project proposal.

Objective 1 To identify and quantify fundamental chemical, physical, and biological processes relevant to agricultural pesticides and pharmaceuticals in the environment. USDA-ARS-Maricopa, Az 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. USDA-ARS - Morris, MN In hilly landforms subject to long-term cultivation, erosion has denuded upper slope positions of topsoil and accumulated topsoil in lower slope positions. One approach to remediate these eroded landforms is moving soil from areas of topsoil accumulation to areas of topsoil depletion, termed here soil-landscape rehabilitation. Rehabilitation resulted in an increase in grain yield of 63-65% in the upper backslope. Results indicate that addition of accumulated topsoil from lower slope positions to eroded upper slope positions can result in large yield increases in upper slope positions and more consistency in crop yields across the landscape. 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 in an eroded landform following application in the fall and in the spring. Despite large differences in soil properties, the rate of metolachlor dissipation from the top 1 m was essentially the same at all landscape positions. The results of this research suggest that fall-applied metolachlor may not provide economic weed control and presents an increased risk of water contamination; therefore, metolachlor should not be applied in the fall in the northern Corn Belt. Information regarding pesticide mobility is critical for the evaluation of pesticide management practices. We used repacked field lysimeters to evaluate the leaching and plant uptake of the herbicides pendimethalin, clopyralid, mecoprop (MCPP), and dicamba following fall and spring application to soil cropped to winter rye (Secale cereale L.). In most fall and spring trials, mass loss of herbicide through leaching was <3% of the amount applied. Based on this 6-year experiment, it appears that clopyralid is the most mobile of the tested herbicides in this soil, followed by dicamba, mecoprop, and pendimethalin. None of the herbicides was present in rye grain or straw at concentrations that exceed current EU or US tolerances. Colorado State University The presence of steroid hormones in Colorados Cache la Poudre River water is being investigated by solid-phase extraction, derivatization, and gas chromatographytandem mass spectrometry (GC-MS/MS). Rainfall simulations were also conducted on an agricultural field applied with municipal biosolids to investigate the potential for steroid hormone runoff and leaching. Laboratory experiments also are being conducted to investigate the potential for steroid hormone biodegradation and photodegradation under simulated natural conditions. Estrogens and androgens were observed at multiple sites along the river. Preliminary data from our rainfall simulation study shows significant concentrations of estrogens, androgens and progestins in the runoff. Androgens and progesterone were found to a larger extent in the runoff than estrogens. Biodegradation of 17²-estradiol, testosterone and progesterone by manure-borne microorganisms in pig manure was observed and multiple degradation products were detected by liquid chromatography time-of-flight mass spectrometry (LC-TOF-MS). Using UV-A lamps direct photodegradation of testosterone and progesterone was observed, and indirect photodegradation of testosterone and 17²-estradiol was observed in the presence of 5 mg/L humic acid. Several novel photodegradation products were observed by mass spectrometry. These findings suggest that steroid hormones are present in the Cache la Poudre River of Colorado, and have the potential to undergo biodegradation and photodegradation. In addition, humic acid (acting as a photosensitizer) can facilitate the indirect photodegradation of some steroid hormones. Finally, our preliminary data shows that steroid hormones have the potential to runoff from agricultural fields applied with biosolids during a heavy rainfall event. Iowa State University Understanding sorption mechanisms and processes is critical for predicting the fate of organic pollutants in soils and for development of effective remediation strategies for contaminated soils. Of particular interest is how organic compounds interact with mineral surfaces that are physically organized with one another in different ways depending on the type of saturating cation and the water content of the system. A novel suspension x-ray diffraction (XRD) technique used to elucidate the influence of the size and swelling of K- and Ca-smectite quasicrystals in aqueous suspensions on adsorption of 4,6-dinitro-o-cresol (DNOC). XRD analysis is a valuable tool for gaining insight into interactions between smectites and organic molecules, but caution must be used in extrapolating data based on XRD patterns of air-dried and oven-dried smectite films to processes that may occur in aqueous smectite suspensions. The fate of organic contaminants in soils and sediments is influenced by sorption of the compounds surfaces of soil materials. The interactions among sorption of an organic compound, cation exchange reactions, and both the size and swelling of smectite quasicrystals were investigated. Results suggest that interactions among cation exchange and organic sorption reactions are controlled by an inherently hysteretic feedback process that is regulated by changes in the size and extent of swelling of smectite quasicrystals. The estrogenic hormones, e.g., 17²-estradiol (E2) and estrone (E1), are regarded as some of the most potent of natural endocrine-disrupting compounds (EDC). At levels of a few ng L-1, E2 and E1 can interfere with normal sexual development in some aquatic species. Both E2 and E1 have been added to soil through livestock waste from concentrated animal feeding operations. However, the fate and transport of these compounds in soils are not easily predicted, partly as a result of analytical challenges at low environmental concentrations and because of weak understandings of adsorption mechanisms at the water-soil interface. The comparisons of sorption parameters (n, Kd, and Koc) over the range of concentrations studied, demonstrate the essentially empirical nature of the models used to assess the interactions of hydrophobic solutes like estrogens and solid-phase sorbents like soil. It is possible to over-interpret the significance of sorption parameters, since they can depend on the concentration range explored and how the sorption reactions themselves affect concomitant reactions such as precipitation or condensation of sorbate molecules. South Dakota State University The runoff potential of tylosin and chlortetracycline from soils was assessed from soils treated with manure from swine fed rations containing the highest labeled rate of each chemical. Slurry manures from the swine contained either chlortetracycline (CTC) at 108 ¼g/g or tylosin at 0.3 ¼g/g. These manures were surface applied to clay loam, silty clay loam, and silt loam soils at a rate of 0.22 Mg/ha. The total amount of CTC collected ranged from 0.9 to 3.5% of the amount applied whereas tylosin ranged from 8.4 to 12%. These data indicate that if surface applied manure contains antimicrobials, runoff could lead to offsite contamination. The data from this study in combination with data from other studies indicate that manure from animals treated with antimicrobial chemicals should be handled carefully. While leaching of these antimicrobial chemicals into and through the soil profile may be limited, their movement in runoff to offsite areas may be an unintended consequence of manure application. Additional studies using manure from swine fed rations with and without CTC and biosolids with and without tetracycline (TET) changed soil microbial diversity and community structure with changes observed out to 42 DAT. The changes observed, in turn, may lead to changes in microbial function. A third study investigated the effects of the 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. Data suggested that swine manure from pigs administered CTC containing feed will take longer to stabilize under anaerobic conditions compared to tylosin or no-antimicrobial treatments. Residual concentrations of CTC are a concern when considering that land application of stabilized manure into the environment is common practice, and may subsequently result in potential dissemination of antimicrobial compounds or antimicrobial-resistant bacteria into the environment. Auburn University There have been increasing concerns regarding antimicrobials in the environment. Sorption of two antimicrobials, sulfadimethoxine (SDM) and ormetoprim (OMP), was investigated in two soils and sand using a series of batch experiments. Currently, limited research exists on the fate of these compounds once they are discharged in human and animal waste. This study showed relatively low sorption of SDM and OMP in two southeastern U.S. soils, suggesting the potential for these compounds to reach surface and ground water. Recent studies have found widespread occurrence of anthropogenic organic compounds in the surface waters in the U.S. Most of these compounds are present at low concentrations and the risks to human and ecosystem health are largely unknown, especially for mixtures of compounds. Catoma Creek is on Alabamas 303(d) list due to organic enrichment and high fecal coliform concentrations. Occurrence of five anthropogenic compounds was monitored for a six-month period in this mixed landuse watershed. Water samples were collected monthly at six sampling sites and analyzed for caffeine, 1,7-dimethylxanthine, acetaminophen, sulfamethoxazole, and DEET (N, N-diethyl-m-toluamide) using LC/MS/MS. All five target compounds were detected in the watershed with DEET, caffeine, and sulfamethoxazole being detected more frequently. One of the six sampling sites was located in an urban area and more target compounds at higher concentrations were found at this site. DEET was detected in all blank samples at an average concentration of 8.7 ng/L. Penn State University Most of the previously reported saturated column experiments conducted to determine sorption of organic chemicals to soil have utilized glass columns, which adsorb very little estrone. However, due to the fragile nature of such glass columns, it is very difficult to connect any additional instruments to measure parameters such as water content and potential. Since these measurements are essential in unsaturated column experiments, an alternative column material was required. A brief sorption test was conducted using 3H-estrone and several different column materials. The materials that were tested included PVC, polycarbonate, type 316 stainless steel, type 302 stainless steel, Teflon, and glass. Polycarbonate, PVC and both types of stainless steel apparently adsorbed estrone. Based on these results, teflon was chosen as the column material for unsaturated column experiments. Connecticut AES Hysteresis, a frequently observed phenomenon in sorption experiments, is inconsistent with the key assumption of sorption reversibility in most fate and bioavailability models. This study of hysteresis has several important implications for the environmental behavior of organic compounds. The results confirm and broaden our previous findings that sorption hysteresis in natural organic matter can be due to creation of long-lifetime metastable states that arise in response to sorbate loading. We have shown that "irreversible" effects are similar for nonpolar aromatic molecules of comparable size; that they depend on concentration; and that this concentration dependence depends on sorbent properties. The results have important implications for modeling solute transport and bioavailability of pollutants because existing models are based on sorption reversibility. The finding that matrix deformation influences uptake and release rates suggests a role for relaxation kinetics in transport models. University of Wisconson Recent research indicates the rapid formation of non-extractable sulfonamide residues and the long-term persistence of these polar antimicrobial agents. Chemical incorporation of sulfonamide antimicrobials into Natural Organic Matter (NOM) may provide an explanation for these reports of apparent non-extractable residue formation. Our results suggest that Michael adduct formation with quinone-like moieties in NOM is likely a more important process for sulfonamide antimicrobial immobilization than are reactions producing Schiff bases. This finding has implications for the environmental stability of bound sulfonamide residues. Bound residues formed by Michael addition reactions are more likely to persist in soil than those formed by Schiff base reactions (e.g., imines); the latter are more easily hydrolyzed in aqueous solution. Reports of non-extractable sulfonamide residues in soil may therefore reflect Michael addition to quinone moieties in soil NOM. The importance of covalent coupling of sulfonamides with NOM vis-à-vis other potential mechanism of non-extractable residue formation warrants investigation. Chemical incorporation of sulfonamide antimicrobials into soil organic matter is expected to diminish their biological activity, and therefore reduce the selective pressure of these compounds for antimicrobial resistant microorganisms. The association of the cationic macrolide antimicrobial clarithromycin (CLA) with dissolved Elliot soil humic acid (ESHA) was investigated as a function of solution chemistry. Despite its low Kow value, CLA+ association with ESHA is similar in magnitude to the binding of many nonpolar organic contaminants (e.g., anthracene, pyrene) with other humic acids. Association of CLA+ (and similar macrolides) with humic acids may afford the antimicrobial(s) protection from degradation processes and reduce bioaccessibility to microorganisms, diminishing potential selective pressure for antibiotic resistant organisms. Association with humic acid may increase the total dissolved concentration of CLA+ in soil and sediment interstitial water, potentially facilitating subsurface transport, and reduces the freely dissolved CLA+ concentration which controls interactions with solid phases and bioavailability. These findings can be extended to complex environmental matrices and soils, while the ability of particulate-bound humic substances to interact with macrolides requires investigation. University of California-Riverside Many pesticides contain stereogenic chiral centers and therefore optical isomers that may have different biological activities or different behaviors (e.g., persistence) in the environment. However, currently chiral pesticides are mostly used as racemates and the chiral selectivity is ignored in risk assessment. Our studies showed that great differences exist in aquatic toxicities as well as biodegradation rates among chiral insecticides and these differences should be considered in risk assessment and regulation. Univeristy of California-Davis Triclosan (TCS) and Triclocarban (TCC) are broad range antibacterial agents widely used in common household products (i.e. shampoo, soap, detergent, toothpaste, cosmetics, sanitizers, etc). Recent research has identified TCS in soil, fish tissue, and human breast milk and has caused the American Medical Association (AMA) to question the necessity and effectiveness of TCS and other antibacterial agents in personal care products. All available evidence suggests that TCS and TCC are likely to accumulate in soils that are amended with biosolids. Preliminary experiments were performed to explore the potential effects on TCS and TCC on soil microbial communities, using phospholipid fatty acid (PLFA) analysis as a screening method. Biomass decreased in both TCS and TCC treatments in comparison to the controls. The decrease of biomass was higher at 100-ug/g TCS and TCC treatments than at 10-ug/g treatments. At low exposures to TCC, the community was no different from an unexposed community, whereas even low exposure to TCS substantially altered the community composition. At higher exposures, both compounds affected the community and the responses were quite variable. In conclusion, the more strongly sorbedTCC had less of an impact than the more water soluble TCS, perhaps due to differences in availability or toxicity. Fungal biomarkers remained unchanged, but abundance of monounsaturated fatty acids decreased in antimicrobial treated soils. Thus this initial characterization of effects demonstrated that significant changes in microbial community could be expected in agricultural soils at concentrations as low as 10-ug/g of TCS and that there may be differences in the impacts of the two antimicrobial compounds. Univiersity of Nebraska-Lincoln Experimental evidence was obtained supporting the formation of nitrosamine derivatives of atrazine (ATR), cyanazine (CYA), simazine (SIM), and desisopropylatrazine (DIA) from reaction with sodium nitrite under acidic aqueous conditions. Optimum temperature programs were also developed for GC-MS analysis of nitrosoatrazine, nitrosocyanazine, nitrososimazine and nitrosodesisopropylatrazine. Although maintaining thermal stability during analysis was a concern, the GC-MS method provides an alternative means of detecting nitrosotriazines. Soil sorption data was obtained for atrazine and nitrosoatrazine. KD values for atrazine and nitrosoatrazine adsorption were 2.5 and 5.4 L/kg. Desorption KDs were 10.0 and 16.7 L/kg, respectively. Based on a soil organic carbon content of 2%, the corresponding Koc values are 125 and 270. These results indicate that the soil retention of nitrosoatrazine is similar to or slightly greater than atrazine. Results of recovery studies of nitrosomorpholine and nitrosoatrazine demonstrated recoveries decreased with increasing soil incubation time. Recoveries after 35 d were 60 and 80%, respectively. Results indicated considerable stability of these nitrosamines in soil. The presence of vitamins B-12 and B-9 resulted in a 50 and 30% reduction in the amount of nitrosoranitidine formed under simulated digestive tract conditions. Vitamins B-12 and B-9 resulted in a 60 and 20% reduction in the amount of nitrosoethambutol formed. The presence and denitrosation of nitrosated compounds in egg yolk may affect the nitric oxide (NO) content within cells, which is critical for normal development. USDA-ARS, St. Paul and University of Minnesota An extraction procedure was identified using aqueous methanol (a water/alcohol mixture) that can characterize triazine herbicide bioavailability in dissimilar aged soils, which in turn may be useful to determine bioavailability of other compounds in soils, especially other related herbicides. Scientists now have 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. This is valuable information for predicting environmental fate and environmental risk assessment. University of California-Berkley Antibiotics were developed to have specific mechanisms of action for well-defined therapeutic purposes, when these compounds are released into the environment they can exhibit unpredicted toxic effects on endogenous soil bacteria and sensitive aquatic organisms. Fluoroquinolone (FQ) antibiotics, exhibit a broad spectrum of activity towards pathogenic bacteria and are widely used in both human and veterinary medicine. They are now detected in surface waters worldwide at concentrations up to 150 ¼M. FQs and related compounds have been shown to affect the growth or species diversity of photosynthetic organisms, including higher plants, phytoplankton, and cyanobacteria. One study reported here appears to be the first to reveal that chloroplasts of photosynthetic organisms are also the inhibitory target of a fluorinated quinolone, ciprofloxacin (Cipro). The results indicated significant reductions in plant growth and development, as well as inhibition of Photosystem II, both of which imply that the antibiotic may deter chloroplast replication by a mechanism related to its antibacterial action and that it may interfere with photosynthetic electron transport. Objective 2 Integrate chemical and biological process information for use in models applicable across different spatial and temporal scales. Incorporating slope and slope length data generated from relatively high resolution 10 m digital elevation models (DEMs), increased sensitivity to topography at the SSURGO polygon level. Although discontinuities occur between counties, model output can identify the most vulnerable areas in each county. The results enhance the ability to correctly identify landscape areas vulnerable to pesticide leaching and runoff in spite of county soil map interpretation differences. Results aid pesticide applicators and environmental managers identify areas most sensitive to surface and ground water contamination so that management practices can be properly targeted to minimize contamination. Objective 3 Provide stakeholders with tools for developing strategies to ensure sustainable agriculture and to protect natural resource systems. Univeristy of California-Riverside Pesticide residues remain on concrete and are available for contaminating runoff for a prolonged time, and the long persistence may be an important cause for non-point source contamination of pesticides in urban watersheds. Clientele (including commercial nurseries in southern California, pesticide applicators, the Regional Water Quality Control Boards, State regulatory agencies - Department of Pesticide Regulation and Department of Food and Agriculture, and county/city water quality managers) may use the research results to implement pesticide TMDLs, and improve water quality in impaired waterbodies in urban and suburban watersheds. University of Nebraska-Lincoln Analysis of survey data revealed significant positive relationships between the use of conservation tillage and instrumental motivation, internal self-concept, and goal internalization, as well as education, farm sales, and percent of income derived from farming. Significant negative relationships were found between conservation tillage and an external self-concept, age, and years of farming. Farmers who believe they cannot maintain autonomous control over farming practices when using conservation tillage are less likely to use the technology. Habitual tendencies are large drivers in conservation tillage adoption decisions. Preferences for control impact the conservation tillage intensity decision. These findings support the idea that an intricate mix of financial incentives and moral suasion may be required to convince farmers to incorporate conservation tillage strategies on working farms.

Accinelli, C., W. C. Koskinen, J. M. Becker, and M. J. Sadowsky. Mineralization of the Bacillus thuringiensis Cry1Ac endotoxin in Soil. J. Agric. Food Chem. 56:1025-1028. 2008. Anhalt, J. C., T. B. Moorman, and W. C. Koskinen. Degradation and sorption of imidacloprid in dissimilar surface and subsurface soils. J. Environ. Sci. Health B. 43:207-213. 2008. Aristilde, L., and Sposito, G. (2008) Molecular modeling of metal complexation by a fluoroquinolone antibiotic. Environ. Toxicol. Chem. 27:2304-2310. Bialk, H.M.; Pedersen, J.A. NMR investigation of enzymatic coupling of sulfonamide antimicrobials with humic substances. Environ. Sci. Technol. 2008, 42, 106-112. Cabrera , A., L. Cox, W. C. Koskinen, and M. J. Sadowsky. Availability of triazine herbicides in aged soils amended with olive oil mill waste. J. Agric. Food Chem. 56:4112-4119. 2008. Chatterjee, R., D.A. Laird, and M.L. Thompson. 2008. Interactions among K+-Ca2+ exchange, sorption of m-dinitrobenzene, and smectite quasicrystal dynamics. Environ. Sci. Technol. 42:9099-9103. Coffelt, T.A. and C.F. Williams. Characterization and recycling of waste water from guayule latex extraction. Industrial Crops Prod. 29:648-653. 2009. Devlin, D. et al. (P.J. Shea). 2008. Pesticide Management for Water Quality Protection in the Midwest. Heartland Regional Water Coordination Initiative. Kansas State University, Manhattan, KS. (http://www.oznet.ksu.edu/library/h20ql2/mf2822.pdf) Farenhorst, A., Papiernik, S. K., Saiyed, I., Messing, P., Stephens, K. D., Schumacher, J. A., Lobb, D. A., Sheng, L., Lindstrom, M. J., and Schumacher, T. E. Herbicide sorption coefficients in relation to soil properties and terrain attributes on a cultivated prairie. J. Environ. Qual. 37:1201-1208. 2008. Feng, Y. 2008. Soil microbiology. In: Encyclopedia of Soil Science, W. Chesworth (ed). Springer Publishing Company, New York, NY. Koskinen, W. C., and P. A. Banks. Soil movement and environmental fate of triazine herbicides. p. 355-385. In H. M. LeBaron, O. C. Burnside, and J. McFarland (eds.) The Triazine Herbicides. Elsevier Science, Amsterdam, The Netherlands. 2008. (Book Chapter) Laird. D. A., and W. C. Koskinen. Triazine soil interactions. p. 275-299. In H. M. LeBaron, O. C. Burnside, and J. McFarland (eds.) The Triazine Herbicides. Elsevier Science, Amsterdam, The Netherlands. 2008. (Book Chapter) Papiernik, S. K., Schumacher, T. E., Lobb, D. A., Lindstrom, M. J., Lieser, M. L., Eynard, A., and Schumacher, J. A. Soil properties and productivity as affected by topsoil movement within an eroded landform. Soil Tillage Res. 102:67-77. 2009. Pereira, T.R., D.A. Laird, M.L. Thompson, C.T. Johnston, B.J. Teppen, H. Li, and S.A. Boyd. 2008. Role of smectite quasicrystal dynamics in adsorption of dinitrophenol. Soil Sci. Soc. Am. J. 72:347-354. Reiman, M., D.E. Clay, C.G. Carlson, S.A. Clay, G. Reicks, D.W. Clay, and D.E. Humburg. 2009. Manure placement depth impacts on crop yields and N retained in soil. J. Envrion. Sci. Health (B). 44:76-85. Regitano, J. B. and W. C. Koskinen. Characterization of nicosulfuron availability in aged soils. J. Agric. Food Chem. 56:5801-5806. 2008. Sakaliene, O., Papiernik, S. K., Koskinen, W. C., Kavoliknaite, I., and Brazenaitei, J. Using lysimeters to evaluate the relative mobility and plant uptake of four herbicides in a rye production system. J. Agric. Food Chem. Accepted Dec. 18, 2008. Sakaliene, O., S. A. Clay, W. C. Koskinen, and G. Almantas. Early Season Weed suppression in buckwheat using clopyralid. Weed Tech. 22:707-712. 2008. Sakaliene, O., W. C. Koskinen, G. Blazauskiene, and I. Petroviene. Level and fate of chlorpropham in potatoes during storage and processing. J. Environ. Sci. Health B. 44:1-6. 2009. Sanders, S.M., P. Srivastava, Y. Feng, J.H. Dane, J. Basile, and M.O. Barnett. 2008. Sorption of the veterinary antimicrobials sulfadimethoxine and ormetoprim in soil. J. Environ. Qual. 37:1510-1518. Sheng, L., Lobb, D. A., Lindstrom, M. J., Papiernik, S. K., and Farenhorst, A. Modeling tillage-induced redistribution of soil mass and its constituents within different landscapes. Soil Sci. Soc. Am. J. 72:167-179. 2008. Sibley, S.D.; Pedersen, J.A. Interaction of the macrolide antimicrobial clarithromycin with disolved humic acid. Environ. Sci. Technol. 2008, 42, 422-428. Walker, C., and H. Lin. 2008. Soil property changes after four decades of wastewater irrigation: A landscape perspective. Catena 73:63-74 Wortmann, C.S. et al. (P.J. Shea). 2008. Targeting of Watershed Management Practices for Water Quality Protection. Heartland Regional Water Coordination Initiative. University of Nebraska-Lincoln, Lincoln, NE. (http://www.ianrpubs.unl.edu/epublic/live/rp195/build/rp195.pdf). Xie, B., S.K. Khanal, J. van Leeuwen, S.W. Veysey, and M.L. Thompson. 2008. Sorption of steroidal hormones by two Iowa soil materials: Detection and modeling. Soil Sci. 173:602-612. Zheng, W., Yates, S. R., and Papiernik, S. K. Transformation kinetics and mechanism of the sulfonylurea herbicides pyrazosulfuron ethyl and halosulfuron methyl in aqueous solutions. J. Agric. Food Chem. 56:7367-7372. 2008.