TECHNICAL REPORTS 794 Elucidating veterinary antibiotic interactions with soil is important for assessing and mitigating possible environmental hazards. he objectives of this study were to investigate the efects of vegetative management, soil properties, and >1000 Da dissolved organic matter (DOM >1000 Da ) on sulfamethazine (SMZ) behavior in soil. Sorption experiments were performed over a range of SMZ concentrations (2.5–50 μmol L -1 ) using samples from three soils (Armstrong, Huntington, and Menfro), each planted to one of three vegetation treatments: agroforestry bufers strips (ABS), grass bufer strips (GBS), and row crops (RC). Our results show that SMZ sorption isotherms are well itted by the Freundlich isotherm model (log K f = 0.44–0.93; Freundlich nonlinearity parameter = 0.59–0.79). Further investigation of solid-to-solution distribution coeicients (K d ) demonstrated that vegetative management signiicantly (p < 0.05) inluences SMZ sorption (ABS > GBS > RC). Multiple linear regression analyses indicated that organic carbon (OC) content, pH, and initial SMZ concentration were important properties controlling SMZ sorption. Study of the two most contrasting soils in our sample set revealed that increasing solution pH (pH 6.0– 7.5) reduced SMZ sorption to the Armstrong GBS soil, but little pH efect was observed for the Huntington GBS soil containing 50% kaolinite in the clay fraction. he presence of DOM >1000 Da (150 mg L -1 OC) had little signiicant efect on the Freundlich nonlinearity parameter; however, DOM >1000 Da slightly reduced SMZ K d values overall. Our results support the use of vegetative bufers to mitigate veterinary antibiotic loss from agroecosystems, provide guidance for properly managing vegetative bufer strips to increase SMZ sorption, and enhance understanding of SMZ sorption to soil. Sulfamethazine Sorption to Soil: Vegetative Management, pH, and Dissolved Organic Matter Efects Bei Chu, Keith W. Goyne,* Stephen H. Anderson, Chung-Ho Lin, and Robert N. Lerch S ulfamethazine (4-amino-N-[4, 6-dimethyl-2-py- rimidinyl] benzenesulfonamide) (SMZ) is one of the sul- fonamide veterinary antibiotics (VAs) commonly used for livestock and aquaculture disease treatment, disease prevention, and growth promotion (Sarmah et al., 2006). In the United States, approximately 3.63 × 10 5 kg of SMZ is used annually as a feed additive for cattle and swine production (Mellon et al., 2001). Like most VAs, SMZ is poorly absorbed and metabo- lized ater entering a human or animal body, and the typical SMZ concentration in manure and manure slurry is on the order of 3 to 35 μmol kg -1 (Haller et al., 2002; Kumar et al., 2005; Burkhardt et al., 2005; Shelver et al., 2010). Sulfamethazine concentrations in soil fertilized with manure range from non- detectable to several micromoles per kilogram (Hamscher et al., 2005; Aust et al., 2008). In surface runof from manured plots, SMZ concentrations can reach 2.5 to 6.8 μmol L -1 (Burkhardt et al., 2005; Kreuzig et al., 2005). Additionally, 1 to 4% of the initial quantity of sulfonamides applied to test plots can be lost via short (<100 min) surface runof events (Burkhardt et al., 2005; Kreuzig et al., 2005). In some cases, VA inputs to soil may afect the quantity and quality of native microbial communities (Kotzerke et al., 2008; Kümmerer, 2003; Nygaard et al., 1992; Westergaard et al., 2001). Although VA concentrations are very low in most soils, they may lead to the increased selection pressure of VA-resistant bacteria in the environment (Kümmerer, 2003; Nygaard et al., 1992). Land application of manure is a primary source of VA release into the environment, resulting in the development of antibiotic-resistant genes within microorganisms (Aarestrup and Wegener, 1999; Herron et al., 1998; Nygaard et al., 1992). For example, multiple tetracycline- and sulfonamide-resistant genes were detected in dairy lagoon water, irrigation ditch water, and urban/agriculturally impacted river sediment samples from northern Colorado (Pruden et al., 2006). Spreading of antibiotic- resistant genes causes public concern that human pathogens will develop antibiotic resistance and be diicult to treat with current antibiotics (Shea, 2003). An additional concern is that SMZ and Abbreviations: ABS, agroforestry bufers strip; CBD, citrate–bicarbonate– dithionite; DOM, dissolved organic matter; GBS, grass bufer strip; HPLC, High- performance liquid chromatography; OC, organic carbon; RC, row crop; SMZ, sulfamethazine; VA, veterinary antibiotic. B. Chu, K.W. Goyne, and S.H. Anderson, Dep. of Soil, Environmental and Atmospheric Sciences, Univ. of Missouri, 302 ABNR Building, Columbia, MO 65211; C.-H. Lin, Center for Agroforestry, Univ. of Missouri, 203 ABNR Building, Columbia, MO 65211; R.N. Lerch, USDA–ARS, Cropping Systems and Water Quality Research Unit, 269 Ag. Eng. Bldg., Columbia, MO 65211. Assigned to Associate Editor K.G. Karthikeyan. Copyright © American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America. 5585 Guilford Rd., Madison, WI 53711 USA. All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. J. Environ. Qual. 42:794–805 (2013) doi:10.2134/jeq2012.0222 Supplemental data ile is available online for this article. Received 30 May 2012. *Corresponding author (goynek@missouri.edu). Journal of Environmental Quality ORGANIC COMPOUNDS IN THE ENVIRONMENT TECHNICAL REPORTS