1a. Objectives (from AD-416):
Objective 1: Update data on levels of dioxins and related compounds in the domestic food supply to provide Food Safety agencies with an adequate profile of the situation and confirm the safety and competitiveness of U.S. foods. Objective 2: Develop inexpensive, rapid, sensitive assays or improved diagnostic tools to screen samples for pesticides and other environmental contaminants such as dioxins. Objective 3: Investigate sources which contribute to levels of these contaminants in food animals, that are, feed components, dust or soils, treated wood, and identify intervention strategies that may reduce the levels. Objective 4: Investigate the uptake, metabolism, distribution, excretion, and fate after excretion of environmental contaminants in animal systems with the goal of developing pharmacokinetic rate and volume constants pertinent to residue depletion modeling and real time calculation of withdrawal intervals to protect both food products and the environment. Subobjectives include in vivo and in vitro metabolism studies and fate and transport in the environment studies.
1b. Approach (from AD-416):
Persistent organic pollutants, e.g. dioxins, dioxin-like compounds, brominated flame retardants, and perfluorinated compounds are ubiquitous environmental contaminants that can enter the food chain as animals are exposed through their surroundings and feeds. Because these compounds can cause numerous health effects in animals including cancers, developmental and neurological problems, and immune and reproductive systems disruptions, U.S. and international health organizations recommend continuing to decrease human exposure by lowering levels in foods and the environment. Our research efforts focus on reducing exposure to these contaminants using four approaches. First, surveys of the general food supply (especially meat, poultry, and farm-raised catfish) will be conducted and will provide background levels of these compounds in U.S. foods, serve as a periodic monitor of domestic foods, and track temporal trends. These data are critical to regulatory agencies for developing risk assessments. Second, rapid, inexpensive assays will be developed for detecting contaminants in food products. If successful, these assays may result in widespread monitoring of the food supply and environment, which currently is not feasible due to the high costs or lack of analytical methods. Third, sources that contribute to livestock exposure throughout the production process will be investigated and cataloged. Once identified, these sources may be eliminated, controlled, or avoided in farming practices. Fourth, basic research to determine pharmacokinetic parameters for these pollutants in laboratory and farm animals, potential remediation methods such as bacterial degradation or composting practices, and transport in soils and into plants will be investigated through controlled laboratory studies. These data will be used to estimate animal withdrawal intervals, evaluate source attribution, and elucidate strategies to decrease contaminant levels in food animals or the environment.
3. Progress Report:
Radiolabeled beta-HBCD was synthesized and sent to collaborators at the NIEHS in Research Triangle Park, NC for the live phase of a metabolism study in mice. Metabolites were characterized and levels of beta-HBCD in excreta quantitated. Radiolabeled alpha, beta and gamma HBCD isomers were synthesized and metabolism studies of each isomer were completed in male rats. Each HBCD isomer has different pharmacokinetics and metabolism. The study lays the groundwork for using unique metabolites as biomarkers for exposure to individual HBCD isomers. Scientific presentations of the research have been made. The live-phase of a kinetic study of the industrial surfactant PFOS was completed in cattle. One year after oral administration, PFOS was still detectable in the serum of cattle, indicating its persistence and potential for bioaccumulation. Our laboratory analyzed mouse liver and aorta samples for polyunsaturated fatty acids and tetrachlorodibenzo-p-dioxin (TCDD) in support of research being conducted at the University of New Mexico on the toxicity of TCDD and its role in cardiovascular disease. The major bacteria from dioxin-contaminated soils were isolated and identified. Bacterial isolates capable of growing on a dioxin media as a sole carbon source were then inoculated into contaminated soils to determine if they were capable of degrading toxic dioxins. Under the conditions of the study, the degradation of dioxins in inoculated soil was minimal, and therefore, the bacteria were not considered viable for remediation purposes. A cutting-edge immunoassay was developed for the simultaneous detection of polycyclic aromatic hydrocarbons, polychlorinated biphenyls, and polybrominated diphenyl ethers in buffer and fish extracts. The sensitivities of the immunoassays for marker analytes in buffer were the very similar to those in fish tissues containing fat. The performance of the immunoassay, in combination with a co-developed tissue extraction procedure, is adequate for regulatory control.
1. Pharmacokinetics of the industrial contaminant perfluorooctane sulfonate in beef cattle. Perfluorooctane sulfonate (PFOS) is a "nonstick" surfactant used in many industrial, commercial, and consumer products. Due to its extensive use, PFOS is widely found in humans, wildlife, and the environment. Cattle are exposed to PFOS while grazing in contaminated areas, but the extent to which PFOS accumulates in their meat is not known. ARS researchers at Fargo, ND, together with scientists at the USDA Food Safety and Inspection Service and North Dakota State University, conducted a metabolism study to determine the degree to which PFOS concentrates in the edible tissues of beef cattle and whether PFOS residues may be a concern for human exposure. The PFOS was not readily excreted, and nearly half of the total dose was still in the blood a month after dosing. PFOS was detected in edible tissues. This study showed that PFOS would likely accumulate in beef exposed to environmental PFOS and that consumption of contaminated beef could be a source of human exposure to PFOS.
2. Survey of market catfish for the presence of dioxins and source attribution. The USDA is responsible for the safety of meat, poultry, egg, and catfish products sold in the United States. Animal-based food products are the major route of exposure to dioxins for humans, and one way to reduce that exposure is to identify and remove the sources of dioxin before they enter the food chain. USDA ARS scientists in Fargo, ND measured 17 individual dioxin compounds in catfish tissues. These data demonstrated that dioxin levels found in the catfish products were low and suggested minimal public health risks; however, they also suggested that uncontaminated mineral clays or alternatives to mineral clays in catfish feeds would minimize even further the entrance of dioxins to the food supply.
Meimaridou, A., Kalachova, K., Shelver, W.L., Franek, M., Pulkrabova, J., Haasnoot, W., Nielen, M.W.F. 2011. Multiplex screening of persistent organic pollutants in fish using spectrally encoded microspheres. Analytical Chemistry. 83:8696-8702.