Submitted to: Dioxin Meeting
Publication Type: Proceedings
Publication Acceptance Date: 6/1/2011
Publication Date: 8/21/2011
Citation: Lupton, S.J., Huwe, J.K., Smith, D.J., Dearfield, K., Johnston, J.J. 2011. Absorption and excretion of 14C-perfluorooctanoic acid (PFOA) and perfluorooctane aulfonate (PFOS) in beef cattle. Dioxin 2011. 31st International Symposium on Halogenated Persistent Organic Pollutants POPs’ Science in the Heart of Europe, August 21-25, 2011, Brussels, Belgium. Organohalogen Compounds. 73:1150-1153. Available: http://www.dioxin20xx.org/query.cfm Interpretive Summary: Perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) are industrial chemicals used in a wide range of products as surfactants and coatings, such as Teflon® and Scotchgard™. PFOA and PFOS are widely spread in the environment and are found in humans and wildlife. Because these chemicals appear to accumulate in the body it is important to understand routes of exposure for humans. Due to the fact that biosolids containing PFOA and PFOS from wastewater treatment plants are spread on cattle pastures and animal food crops it is important to know to what extent agricultural animals such as cattle absorb and accumulate PFOA and PFOS. For these reasons we have conducted a study to look at the absorption, distribution and excretion of PFOA and PFOS in beef cattle. After a single oral dose of PFOA and PFOS to Angus steers, we determined that PFOA is excreted in the urine relatively quickly (within 1 week), whereas PFOS remained at elevated levels in the blood throughout the 28 day study. PFOS was readily absorbed and distributed into the tissues of the cattle. The results from this study show that accumulation of PFOS in beef cattle is possible and the food supply could be a possible route of exposure for humans.
Technical Abstract: Perfluoroalkyl compounds such as perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS) are industrial chemicals that are environmentally persistent. Both PFOS and PFOA are found in biosolids, and the application of these contaminated biosolids to pastures has raised concerns about possible human exposure through the accumulation of PFOA and PFOS in edible tissues of these animals. As such, the United States Department of Agriculture (USDA) has undertaken a study to determine the absorption, distribution, metabolism, and excretion of PFOA and PFOS in beef cattle following oral exposure. A study protocol was developed and approved by the Institutional Animal Care and Use and the USDA Radiation Safety Committees. Four Lowline Angus steers (281 – 366 kg) were given single oral bolus doses containing 14C-labeled PFOA (1 mg/kg, 0.6 mCi per steer) and unlabeled PFOS (10 mg/kg). Serum and plasma were collected from each steer prior to and at various intervals after dosing. Quantitative urine and fecal collections were made during the same period every day from each steer. Cattle were slaughtered 28 days after dosing. Radioactivity in the serum, plasma, and urine was determined by liquid scintillation counting (LSC) and in the feces and tissues by combustion analysis followed by LSC. PFOA and PFOS concentrations were determined by liquid chromatography-quadrupole time of flight mass spectrometry (LC-QToF). 14C-PFOA derived radioactivity was completely absorbed and excreted in the urine within 8 days of dosing (100.6 ± 3.3% of the dose). LC-QToF analysis confirmed that the majority of 14C was parent PFOA and not metabolites. Radiocarbon in blood and urine peaked between 24 and 36 hrs post dose. Minimal amounts of radioactivity were excreted in the feces (2-3%) and no PFOA derived radioactivity was detected in tissues. In contrast to PFOA, urinary excretion of PFOS was minimal (0.054 ± 0.0071% of the dose). PFOS in urine and plasma peaked about 2-3 days post-dose and remained elevated in urine and plasma through the course of the study. Studies in rodents and non-human primates have estimated PFOA half-lives of 10-30 d. One exception is female rats which have rapid urinary excretion rates with half lives of 3-5 hr. Our data indicated that PFOA is rapidly excreted by steers with a half-life of 24 hr and would be unlikely to accumulate in edible tissues. PFOS half-lives are longer than that of PFOA, for non-human primates it is estimated at 200 days and for humans it is on the order of years. PFOS levels in this study remained elevated indicating a half-life much longer than 28 days and that PFOS accumulation in edible tissues is likely. Tissues and feces from this study are currently being analyzed for PFOS.