1a. Objectives (from AD-416)
Objective 1. Investigate the kinetics of uptake, metabolism, distribution, and excretion of chemicals in food animals with the goal of reducing public exposure to chemical residues in food animal products (milk, meat, eggs). Objective 2. Determine the fate of endogenous reproductive hormones, pharmaceuticals, and other chemicals in wastes of food animals, including transport through soil and water. Objective 3. Develop sensitive and accurate analytical tools to rapidly detect and quantify chemicals identified in objectives 1 and 2.
1b. Approach (from AD-416)
The broad objective of this project is to determine the fate of natural and man-made chemicals in food animals and in food animal systems (wastes, soil, water). Three broad classes of chemicals will be targeted for study: (1) veterinary drugs or feed additives administered to food animals under extra-label use conditions, (2) endogenous steroid hormones, and (3) novel developmental chemicals of potential utility to the livestock industry. Use of veterinary chemicals in an extra-label manner without knowledge of residue depletion kinetics has led to unsafe residues in meat products. Endogenous steroid hormones excreted by livestock are highly potent endocrine-disrupting compounds that are thought to disrupt the development of aquatic species after their entry into surface waters. Finally, chemical technologies developed by the ARS, e.g., chloroxyanions and nitro compounds, are active against Salmonella and E. coli pathogens in livestock immediately prior to slaughter, but the impacts of chemical residues in meat products have not been fully investigated for these compounds. Regardless of the chemical class being investigated, the development of sensitive and accurate analytical tools is critical completion of the objectives. Therefore, a significant portion of the project is devoted to developing the analytical tools required to ensure success of the project. The overall project goal is to understand the broad impact that chemical residues play in influencing food and environmental safety.
3. Progress Report
Several hundred fecal, milk, urine, and serum samples were assayed for chlorate content as a portion of a study to understand how oral administration of sodium chlorate reduces numbers of pathogens in live animals. The data clearly indicate that chlorate is rapidly and extensively absorbed from the gastrointestinal tracts of sheep to the extent that very little chlorate remains in large intestine contents or feces. These data suggest that the efficacy of chlorate salts is not dependent upon its presence in the lower gastrointestinal tract. We determined that the steroid hormone estradiol is associated with colloidal particles in swine lagoon wastewater and have developed a method to isolate colloid-bound estradiol from estradiol dissolved in solution. Further work using fluorescence polarization methods will assess the ability of estrogen-colloid complexes to interact with estrogen receptors. These data will be used to evaluate the biological activity and stability of estrogens bound to colloidal particles. Radiolabeled 17-beta-estradiol-17-sulfate (E2-17S) was synthesized and shown to resist degradation in soil in comparison to estradiol-3-glucuronide. Although a small percentage of E2-17S was degraded to parent estradiol, the most common degradation products were the result of oxidation. The study indicates that estradiol present in ground or surface water is more likely derived from the hydrolysis of estradiol glucuronides than estradiol sulfates. In addition, the study showed that all estradiol conjugates are readily transported in water and are not sorbed to soil. Roxarsone haptens, immunogens, and antibodies were generated and the antibodies were tested towards their activity against roxarsone. The best antigen/antibody combination was used to develop an enzyme linked immunsorbent assay which was sensitive towards roxarsone and had minimal recognition of other structurally related compounds. The newly developed assay is economical, rapid, and user friendly when compared to traditional instrumental methods used for quantitative analysis of roxarsone. Beet by-products were found to contain highly variable amounts of estrogenic activity, and some contained sufficient concentrations to impact reproductive efficiency in cattle. The estrogenic activity of the beet byproducts correlated with the content of zearalenone, a fungal mycotoxin. Wet harvest and storage conditions may increase the fungal and zearalenone content of beets and feeding poorly stored beet products to cattle may reduce reproductive efficiency.