Predicting Perchlorate Exposure in Milk from Concentrations in Dairy Feed CLIFFORD P. RICE,* ,† RANSOM L. BALDWIN VI, § LINDA C. ABBOTT, § CATHLEEN J. HAPEMAN, † ANTHONY V. CAPUCO, ‡ ANH LE, † KRYSTYNA BIALEK-KALINSKI, † DOUGLAS D. BANNERMAN, ‡ WILLIAM R. HARE, | MAX J. PAAPE, ‡ GREGORY W. MCCARTY, ⊥ ADAM C. KAUF, ‡ ALI M. SADEGHI, ⊥ JAMES L. STARR, ⊥ LAURA L. MCCONNELL, † AND CURTIS P.VAN TASSELL ‡ Environmental Management and Byproduct Utilization Laboratory, Bovine Functional Genomics Laboratory, Veterinary Services, Hydrology and Remote Sensing Laboratory, USDA, Agricultural Research Service, Beltsville, Maryland, 20715, and Office of Risk Assessment and Cost-Benefit Analysis, USDA, Washington, D.C. 20250. Perchlorate has been detected in U.S. milk samples from many different states. Applying data from a recently reported 9-week experiment in which 16 Holstein dairy cows were administered perchlorate allowed us to derive an equation for the dose-response relationship between perchlorate concentra- tions in feed/drinking water and its appearance in milk. Examination of background concentrations of perchlorate in the total mixed ration (TMR) fed in addition to the variable dose supplied to treated cows as a ruminal infusate revealed that cows receive significant and variable exposure to perchlorate from the TMR. Weekly examination of the TMR disclosed that a change in ingredients midway through the experiment caused a significant (78%) change in TMR perchlorate concentration. Analyses of the ingredients comprising the TMR revealed that 41.9% of the perchlorate came from corn silage, 22.9% came from alfalfa hay and 11.7% was supplied by sudan grass. Finally, USDA Food and Nutrition Survey data on fluid milk consumption were used to predict potential human exposure from milk that contained concentrations of perchlorate observed in our previous dosing study. The study suggests that reducing perchlorate concentration in dairy feed may reduce perchlorate concentrations in milk as well as the potential to reduce human exposure to perchlorate in milk. KEYWORDS: Perchlorate; milk; dairy cows; dairy feed; human exposure INTRODUCTION Perchlorate was first identified as a chemical of concern by the Environmental Protection Agency (EPA) in 1985 following its discovery in wells at hazardous waste sites in California (1). It was not until the advent of more sensitive detection methods in 1997 that states began testing for, and finding, perchlorate in ground and surface waters (2, 3). Recent studies on effect of perchlorate on human health have shown perchlorate consump- tion may affect the thyroid by decreasing the absorption of iodine (2). Iodine deficiency can lead to developmental delays in fetuses and infants (2). The Environmental Protection Agency recently established a dietary reference dose (RfD) for perchlo- rate at 0.0007 mg/kg body weight/day to account for perchlorate exposure from both food and water (4). Perchlorate has been detected in surface and groundwater from several western states (2). Perchlorate was reported as an unregulated contaminant in public drinking water systems in 26 states and two commonwealths during 2001 to 2003 (1). Salts of perchlorate are extremely soluble. This fact coupled with perchlorate’s very low sorption and low biotransformation make perchlorate very mobile in surface and groundwater. Some major sources of environmental contamination by perchlorate in the U.S. are associated with activities of the military or defense industry (5). Ammonium perchlorate is used as a solid oxidant in rocket propulsion. Ammonium perchlorate is also used as oxidizer in fireworks and road flares (6). A former ammonium perchlorate production facility located in Henderson, Nevada (near Las Vegas) has been identified as the primary source of contamination to Lake Meade and the lower Colorado River (3). Perchlorate can also occur naturally in nitrogen-rich mineral deposits and has been found in Chilean nitrate fertilizers (1). Some recent data suggest that natural atmospheric processes * Corresponding author phone: (301)-504-6398; fax: (301)-504-7976; e-mail: clifford.rice@ars.usda.gov. † USDA - Environmental Management and Byproduct Utilization Laboratory. § USDA - Bovine Functional Genomics Laboratory. ‡ USDA - Office of Risk Assessment and Cost-Benefit Analysis. | USDA - Veterinary Services. ⊥ USDA - Hydrology and Remote Sensing Laboratory. 8806 J. Agric. Food Chem. 2007, 55, 8806–8813 10.1021/jf070953h This article not subject to U.S. Copyright. Published 2007 by the American Chemical Society Published on Web 09/25/2007