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:
Objective 1. Kidney inhibition swab tests and LC-MS/MS were used to evaluate the depletion of penicillin G residues from kidney, skeletal muscle, serum, and urine of heavy sows. Correlations were drawn between tissue and urine residues. Tissue depletion data were used to estimate withdrawal periods required for the depletion of penicillin residues from edible tissues. Studies investigating chlorine dioxide-related residues on vegetable matter during fumigation were conducted. Effects of gas concentration and exposure to light on chlor-oxyanion levels in rinse fractions and in edible tissues were measured. Chlorate levels were measured in blood, drinking water, and uterine fluid of sheep that had been dosed with single or multiple doses of sodium chlorate. Analytical methods included ion chromatography and LC-MS/MS. Objective 2. The fate and transport of ractopamine HCl were determined in two soil types using sterile and non-sterile conditions. Soils employed were of relevance to agronomic practices in the Midwest region of North America. Both the sorption and degradation of ractopamine HCl and were measured. Greenhouse studies were also conducted to determine the uptake of ractopamine HCl by alfalfa and wheat from Midwestern soils. The presence of ractopamine in edible plant parts was measured subsequent to plant maturation. The fate of estradiol-sulfate (E2S) in a soil-water system was studied in sterile and non-sterile soil, and with soils of high and low organic content. The contribution of each soil variable to E2S degradation, sorption, and transport in water was measured. Background estrogens in ground and surface water samples from sites not impacted by agricultural practices for over a decade have been measured. Additionally, water samples from fields receiving their first application of estrogen-laden manures are being analyzed. Estrogenic activity in serum from a number of food-animal species including sheep, cattle, swine, and catfish was measured using an in vitro E-screen bioassay. The bioassay was tested for its ability to detect estrogenic activity under normal physiologic conditions and when animals were exposed to natural and man-made dietary estrogens. Estrogenic activity in serum from mares exposed to a fungal estrogen was also evaluated. In an interagency collaboration, the estrogenic activity in 19 streams distributed across 12 US states was surveyed. The streams were in proximity to dairy, grazing, or feedlot cattle; swine, or poultry operations; and 4 areas without livestock (or livestock manure application). Estrogenic activities of all watersheds were consistently below the United Kingdom's proposed Lowest Observable Effect Concentration for estradiol in fish (10 ng/L), regardless of land use. Objective 3. Analytical methods based on UPLC-MS or UPLC-MS/MS were developed and/or improved for the detection of chlorate salts in a number of food matrices including vegetables and melons. The methods have been used to support efforts to investigate the fate of chlorate in food animals and to investigate the formation of chloroxyanion byproducts after chlorine dioxide fumigation of vegetables and melons.
1. Systemic effects of chlorate salts on gastrointestinal bacteria. Copious amounts of data have shown that chlorate salts reduce the fecal shedding of pathogens after oral dosing, however several studies have also shown that chlorate salts are nearly completely removed from the intestinal tract by absorption. ARS scientists at Fargo, ND demonstrated that the fecal shedding of E. coli, a marker organism for intestinal pathogens, was significantly reduced when the gastrointestinal tract was bypassed completely and chlorate salts were dosed intravenously. In fact, reductions in fecal shedding of E. coli in intravenously dose animals were identical to orally dosed animals. This is the first study which shows that chlorate salts have physiologic effects on host animals which affect the ability of bacteria to colonize the gastrointestinal tract. Chlorate's mechanism of interacting with a host animal may be exploited to develop better technologies for reducing pathogenic organisms in food animals.
2. Estrogenic activity of layer hen wastewater. Laying hen farms are a potential point source of estrogen entry into the environment due to the high concentration of female animals and the use of wastewater for irrigation purposes. Scientists at the ARS facility in Fargo, ND determined that the estrogenic activity in wastewater at a commercial laying hen facility decreased as wastewater passed through the farm's lagoon system. Waste-water in the final lagoon contained estrogenic activity below predicted no-effect concentrations. The use of egg wash wastewater for irrigation purposes contributes little, if any, to the estrogenic burden of land receiving irrigation waters from layer hen facilities.
3. Precursors to environmental estrogens. Laboratory studies have shown that unconjugated estrogens are short-lived and immobile in soil, which contradicts the fact that estrogens are fairly frequently detected at concentrations of concern in environmental waters. ARS scientists at Fargo, ND demonstrated that sulfate-conjugated estrogens, which are abundant in swine waste, would probably not be a major contributor to free estrogens (estrogen and estrone) in the environment. Unlike glucuronide-conjugated estrogens, estrogen sulfate was relatively stable in a soil-water system with less than 1% of the applied dose being converted to free estrogens. The study shows that estrogen enters the environment through precursors other than estrogen sulfate.
Shrestha, S.L., Casey, F.X.M., Hakk, H., Padmanabham, G. 2013. A radioassay-based approach to investigate fate and transformation of conjugated and free estrogens in an agricultural soil. Environmental Engineering Science. 30:89-96.