Location: Food Animal Metabolism Research
2019 Annual Report
Objectives
Objective 1: Develop and/or validate rapid screening assays for the detection of environmental chemicals relevant to U.S. food production.
Sub-objective 1.A: Development of immunochemically based rapid screening methods for new and emerging persistent organic pollutants.
Sub-objective 1.B: Development of immunochemical purification methods for new and emerging persistent organic pollutants.
Objective 2: Determine levels and sources of dioxins and related compounds in the domestic food supply. Provide food safety agencies with data to confirm or refute the wholesomeness and competitiveness of beef, pork, chickens, turkeys and/or catfish.
Sub-objective 2.A: Conduct a nationally-based survey of PCDD/PCDF/PCB/PBDE levels in the domestic meat supply (beef, pork, chicken, turkey, and/or catfish) by collection of adipose tissues from U.S. slaughter facilities.
Sub-objective 2.B: Identify potential production-based or environmental sources of PCDDs/PCDFs/PCBs/PBDEs in food-producing animals.
Objective 3: Determine the uptake, metabolism (in vitro or in vivo), distribution, excretion, and fate of environmental contaminants with the goal of developing pharmacokinetic rate and volume constants pertinent to residue depletion, selection of marker compounds, and calculation of withdrawal intervals.
Sub-objective 3.A: Characterize the absorption, disposition, metabolism, and excretion (ADME) of POPs in food animals.
Sub-objective 3.B: Identify cellular fractions and enzyme classes responsible for the metabolism and putative dehalogenation of POPs.
Sub-objective 3.C: Characterize the bioavailability of POPs in animal systems from major exposure routes.
Sub-objective 3.D: Determine the fate and transport of POPs through soil during ambient weather conditions.
Sub-objective 3.E: Determine the effect of milk processing on POP concentrations in finished products.
Approach
Ubiquitous environmental contaminants enter the human meat supply when animals are exposed through surroundings and feeds. These compounds, known as persistent organic pollutants (POPs) satisfy the standards for chemicals of concern in that they are persistent, bioaccumulative, globally transported, and toxic. 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 animal and human exposures to these contaminants using three approaches. First, we will develop rapid, inexpensive assays and cleanup tools for isolating and detecting POPs in food products. These assays could result in broad monitoring of the food supply, which currently is not feasible due to the high analysis costs. Second, we will continue to survey the U.S. meat supply (beef, pork, chicken, turkey and/or catfish) for POPs, and will track current levels with trends measured over the last two decades. These data are critical to regulatory agencies for risk assessment, and have revealed POP sources that have contributed to livestock exposures and contamination. Once identified sources of contamination may be eliminated or avoided. Third, we will perform basic research to determine pharmacokinetic parameters for POPs in laboratory and farm animals and will develop potential remediation methods using animal feeding studies. We will use these data to calculate withdrawal intervals, and elucidate strategies to decrease contaminant levels in food animals.
Progress Report
This is the final report for project 3060-32420-002-00-D, “Environmental Chemical Residues and their Impact in the Food Supply” which will merge with project, 3020-32420-001-00D, “Detection and Fate of Chemical and Biological Residues in Food and Environmental Systems” at the end of fiscal 2019.
With respect to Objective 1, “Develop and/or validate rapid screening assays for the detection of environmental chemicals relevant to U.S. food production”, progress was made with European cooperators in developing and validating electrochemical immunogenic (antibody based) chemical assays for polybrominated flame retardants (PBFRs) and investigating the best extraction methods for use of the assay. Further, a multiplex fluorescent microarray was developed for measuring a variety of contaminants, including polybrominated flame retardants, in aqueous matrices. Although antigens towards several specific PBFRs (2-ethylhexyl 2,3,4,5-tetrabromobenzoate, TBB; di(2-ethylhexyl)-2,3,4,5-tetrabromophthalate, TBPH) were synthesized, the antibodies produced were not of sufficient sensitivity. Thus, immunochemical screening and quantitative immunoassays were not developed for TBB and TBPH. Progress was made, however on rapid screening and semi-quantitative assays based on hyphenated mass spectrometric methods. For example, brominated estrogens, perflurooctanesulfonate (PFOS), and perfluorohexanesulonate (PFHxS) were successfully measured in environmental and animal matrices using electrospray ionization inlet (ESII) mass spectrometry; the successful demonstration of the technique suggests wide applicability across a variety of important food animal matrices. Brominated estrogens were also measured in environmental matrices using Atmospheric Solids Analysis Probe (ASAP) mass spectrometry. Neither ASAP nor ESII mass spectrometric technique employs chromatographic separation; analytes are measured directly in sample matrices or simple sample extracts. Both techniques provide rapid quantitative or semi-quantitative results.
Objective 2, “Determine levels and sources of dioxins and related compounds in the domestic food supply. Provide food safety agencies with data to confirm or refute the wholesomeness and competitiveness of beef, pork, chickens, turkeys and/or catfish”, has been investigated in cooperation with the USDA Food Safety and Inspection Service (FSIS). Results of the 2012/2013 survey of dioxins in the US meat supply, which demonstrated a continued trend for a reduction in overall dioxin content of meats produced in the U.S., were summarized and reported during the lifetime of this project plan. An additional survey is currently in progress with the addition of the assessment of a cohort of beef liver samples and Siluriformes (catfish) muscles. Tissues from the 2012/13 survey were also assayed for the presence of a series of polybrominated diphenyl ether (PBDEs) flame retardants that are known to accumulate in animal tissues. An overall decline (25.9 to 70.0%) in the median content of total PDBEs in all four meat classes was measured. PPDE content of U.S. meats gathered during the current survey are also being assessed. An additional cooperative project with the USDA FSIS was initiated designed to characterize residues of perfluorooctanoic acid (PFOA), perfluorooctane sulfonate (PFOS) and other perfluoroalkyl contaminants in dairy cattle that were chronically exposed to contaminated drinking water. Data from this study were used to develop models of contaminant depletion from blood, edible tissues, and milk.
The multi-step approach of Objective 3, “Determine the uptake, metabolism (in vitro or in vivo), distribution, excretion, and fate of environmental contaminants with the goal of developing pharmacokinetic rate and volume constants pertinent to residue depletion, selection of marker compounds, and calculation of withdrawal intervals” required a systematic approach. To this end, organic syntheses were required to prepare radiolabeled target compounds including decabromodiphenyl ether (BDE-209), 2,2’,4,4’,5-pentabromodiphenyl ether (BDE-99), and 2,2’,4,4’,5,5’-hexabromodiphenyl ether (BDE-153). These compounds were orally dosed to laying hens and the overall fate and distribution of each was measured in tissues, excreta, and eggs. Remarkably over 25% of some of the dosed BDEs were transferred to eggs during the 7-day study period. Additionally, syntheses were conducted to produce bromo-chloro mixed halogenated dioxins for use in animal disposition studies. Although demanding with respect to resources, studies such as these provide unambiguous data on the rate and extent to which chemical contaminants may be transferred into food-animal products. Additional studies were completed that investigated the absorption and tissue distribution of dust-bound brominated flame retardants in rats. This study was conducted because a significant route of exposure in humans to such flame retardants is via the ingestion of household dust. Another series of studies investigated the soil transport, soil-to-alfalfa, and alfalfa-to-rat transfer of PFOA. These studies provided the first evidence that plant root systems can delay the transport of the perfluoroalkyl contaminants through the soil. Further, forage crops such as alfalfa, may serve to remediate contaminated soils because the contaminant was transported primarily to the above ground portions of the plant (which can be harvested). The partitioning of environmental contaminants and agrochemicals into economically important fractions of milk (i.e., skim milk, curd, whey, whey proteins) was studied using approximately 27 compounds. Data from the study were used to develop a first-of-kind predictive model based on chemical characteristics such as the octanal/water partition coefficient.
Accomplishments
Review Publications
Kraft, A.L., Lacher, D.W., Shelver, W.L., Sherwood, J.S., Bergholz, T.M. 2017. Comparison of immunomagnetic separation beads for detection of six non-O157 Shiga toxin-producing Escherichia coli serogroups in different matrices. Letters in Applied Microbiology. 65(3):213-219. https://doi.org/10.1111/lam.12771.
Romanelli, S., Bettazzi, F., Martellini, T., Shelver, W.L., Cincinelli, A., Galarini, R., Palchetti, I. 2017. Evaluation of a QuECHERS-like extraction approach for the determination of PBDEs in mussels by immuno-assay-based screening methods. Talanta. 170:540-545. https://doi.org/10.1016/j.talanta.2017.04.027.
