Objective 1: Develop and (or) validate sensitive and accurate analytical tools to rapidly detect and quantify chemicals in food animals, food animal products, or other foods. Objective 2: Investigate the kinetics of uptake, metabolism, distribution, and (or) the elimination of chemicals in and from food animals and (or) produce with the goal of reducing public exposure to chemical residues in foods. Objective 3: Determine the fate of endogenous reproductive hormones, antibiotics, and or other chemicals, including biologically-active metabolites or degradation products in wastes of food animal or in food processing systems. Objective 4: Develop and/or validate rapid screening assays for the detection of environmental chemicals relevant to U.S. food production. Objective 5: 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. Objective 6: 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.
The broad objective of this project is to determine the fate of natural and manmade 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.
Substantial progress was realized for all objectives and subobjectives in the project plan. With respect to Objective 1, “Develop and(or) validate sensitive and accurate analytical tools to rapidly detect and quantify chemicals in food animals, food animal products, or other foods” we have expended substantial effort developing atmospheric pressure-based mass-spectrometric assays for environmental and veterinary chemicals. Specifically, we have applied atmospheric solids analysis probe (ASAP), direct analysis in real time (DART), and electrospray ionization inlet ionization (ESII) mass spectrometric technologies to the semi-quantitative determination of chemical residues in urine and tissues of food animals. These techniques are very rapid (typically less than 10 minutes per sample, including sample preparation time) and selective for a wide range of environmental contaminants and for chemicals used in veterinary practice. Such assays have been, and continue to be, validated using incurred chemical residues in animal matrices. Substantial work has been done in validating immunochemically-based rapid screening assays for allergens in foods including ready-to-eat meat products. Progress towards Objective 2, “Investigate the kinetics of uptake, metabolism, distribution, and (or) the elimination of chemicals in and from food animals and (or) produce with the goal of reducing public exposure to chemical residues in foods”, is continuing. Flunixin metabolism (rates, metabolite production, and cytochrome characterization) in hepatic microsomes from cows with detectable antibiotic residues at slaughter (KIS+) and from cows without antibiotic residues (KIS-) was compared. Further, studies investigating the effects of chlorine dioxide gas on fumonisin toxins on contaminated corn were completed as were studies investigating the fate of chlorine dioxide gas on eggs, onions, avocados, and sweet potatoes. The fate of estrogens and estrogenic activity in soils amended with swine and poultry manure has been completed as have studies characterizing the estrogenic activity of some common foods (tofu, beef, rice, milk). Investigation of a possible role of estrogens in the early maturation of salmon in recirculating aquaculture systems was conducted, involving analysis of estrogenic activity of holding waters. Cooperative research evaluated estrogenic activity of water samples collected from the Ganga River (India); this project included an assessment of chemical components in water samples (plasticizers, steroids, and other environmental contaminants). Estrogenic equivalency factors were derived for the various phthalate compounds and bis-phenol A identified in the Ganga River. Studies on estrogens fall under the auspices of Objective 3, “Determine the fate of endogenous reproductive hormones, antibiotics, and or other chemicals, including biologically-active metabolites or degradation products in wastes of food animals or in food processing systems”.
1. Pork products free of chemical residues. Pork kidneys tend to concentrate veterinary drugs and other chemicals prior to their excretion and are therefore commonly used for monitoring violative drug residues. Research scientists at the Agricultural Research Service in Fargo, North Dakota, determined the occurrence of five commonly used animal health drugs in 1040 pork kidneys bought from retail markets. Using highly sensitive assay methods, none of the pork kidneys contained violative drug residues, and most of the kidneys contained no detectable drug residue. These data confirm that veterinary drug residues are usually absent in pork kidney available to consumers and fall well below regulatory thresholds when detected by highly sensitive analytical methods.
2. Contamination-level drug detection. Zilpaterol is a cattle feed additive banned by many U.S. trade partners, competitive sports organizations (animal and human), and livestock trade shows. Additionally, zilpaterol in food animals other than cattle is strictly proscribed. Research scientists at the Agricultural Research Service in Fargo, North Dakota, demonstrated that modern analytical methods are sufficiently sensitive, such that even trace-level zilpaterol exposures (commensurate with accidental exposures) can cause positive chemical residue tests in animal tissues. Sheep exposed to as little as one-thousandth of the normal zilpaterol dose could be positively identified using a variety of modern analytical tools. The data clearly confirm that animals exposed to the equivalent of trace-level zilpaterol contamination would likely test positive using a variety of common analytical methods.
3. Age-related drug metabolism in cattle. Flunixin is an effective anti-inflammatory agent commonly used in dairy cows that is approved by the U.S.-Food and Drug Administration. When used, cattle producers must wait 4 days from the last flunixin treatment to market animals for use as meat. However, flunixin residues exceeding the allowable level (set by the FDA) are one of the most common residue violations in dairy cattle. Dairy cattle are typically harvested at a much older age than beef cattle, because they can produce milk for up to 10 years. Agricultural Research Service scientists in Fargo, North Dakota, demonstrated that rates of flunixin metabolism in liver fractions of older (4 years or greater) cows were lower than in younger (2.5 years or less) steers and heifers. These findings support the theory that high flunixin residues in some dairy cows might, in part, be caused by age-related slowing of flunixin metabolism.
Chakrabarty, S., Shelver, W.L., Hakk, H., Smith, D.J. 2018. Atmospheric solid analysis probe and modified desorption electrospray ionization mass spectrometry for rapid screening and semi-quantification of zilpaterol in urine and tissues of sheep. Journal of Agricultural and Food Chemistry. 66(41):10871-10880. https://doi.org/10.1021/acs.jafc.8b03925.
Shappell, N.W., Duke, S.E., Bartholomay, K.A. 2019. In vitro subcellular characterization of flunixin liver metabolism in heifers, steers, and cows. Research in Veterinary Science. 123:118-123. https://doi.org/10.1016/j.rvsc.2018.12.012.
Shelver, W.L., Mcgarvey, A.M. 2019. Assessment of veterinary drugs present in pork kidney purchased from a Midwest US retail market. Food Additives & Contaminants: Part A. 36(4):571-581. https://doi.org/10.1080/19440049.2019.1586455.
Casey, F.X., Selbie, D., Hakk, H., Richards, K.G. 2019. Leaching of free and conjugate natural estrogens in soil monoliths. Water, Air, and Soil Pollution. 230:49. https://doi.org/10.1007/s11270-019-4079-z.
Smith, D.J., Shelver, W.L., Chakrabarty, S., Hoffman, T.W. 2019. Detection and quantification of residues in sheep exposed to trace levels of dietary zilpaterol HCl. Food Additives & Contaminants: Part A. 36(9):1289-1301. https://doi.org/10.1080/19440049.2019.1627005.
Shelver, W.L., Lupton, S.J., Shappell, N.W., Smith, D.J., Hakk, H. 2018. Distribution of chemical residues among fat, skim, curd, whey, and protein fractions in fortified, pasteurized milk. ACS Omega. 3(8):8697-8708. https://doi.org/10.1021/acsomega.8b00762.