Exposure and effects assessment of resident mink (Mustela vison) exposed to polychlorinated dibenzofurans and other dioxin-like compounds in the Tittabawassee River basin, Midland, Michigan, USA

Authors

  • Matthew J. Zwiernik,

    Corresponding author
    1. Department of Zoology, National Food Safety and Toxicology Center, 224 National Food Safety and Toxicology Building, Michigan State University, East Lansing, Michigan 48824, USA
    • Department of Zoology, National Food Safety and Toxicology Center, 224 National Food Safety and Toxicology Building, Michigan State University, East Lansing, Michigan 48824, USA
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  • Denise P. Kay,

    1. ENTRIX, 4295 Okemos Road, Okemos, Michigan 48864, USA
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  • Jeremy Moore,

    1. Department of Zoology, National Food Safety and Toxicology Center, 224 National Food Safety and Toxicology Building, Michigan State University, East Lansing, Michigan 48824, USA
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  • Kerrie J. Beckett,

    1. Woodlot Alternatives, 122 Main Street, Topsham, Maine 04086, USA
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  • Jong Seong Khim,

    1. Department of Biomedical Veterinary Sciences and Toxicology Centre, University of Saskatchewan, Saskatoon, Saskatchewan S7J 5B3, Canada
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  • John L. Newsted,

    1. ENTRIX, 4295 Okemos Road, Okemos, Michigan 48864, USA
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  • Shaun A. Roark,

    1. ENTRIX, 4295 Okemos Road, Okemos, Michigan 48864, USA
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  • John P. Giesy

    1. Department of Zoology, National Food Safety and Toxicology Center, 224 National Food Safety and Toxicology Building, Michigan State University, East Lansing, Michigan 48824, USA
    2. Department of Biomedical Veterinary Sciences and Toxicology Centre, University of Saskatchewan, Saskatoon, Saskatchewan S7J 5B3, Canada
    3. Department of Biology and Chemistry, City University of Hong Kong, Kowloon, Hong Kong, Special Administrative Region, China
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  • Published on the Web 4/24/2008.

Abstract

Historically, sediments and floodplain soils of the Tittabawassee River (TR; MI, USA) have been contaminated with polychlorinated dibenzofurans (PCDFs), polychlorinated dibenzo-p-dioxins (PCDDs), and polychlorinatedbiphenyls (PCBs). Median concentrations of 2,3,7,8-tetrachlorodibenzo-p-dioxin equivalents (TEQs) based on 2006 World Health Organization tetrachloro-dibenzo-p-dioxin toxic equivalency factors (TEFs) in the diet of mink (Mustela vison) ranged from 6.8 × 10−1 ng TEQ/kg wet weight upstream of the primary source of PCDF to 3.1 × 101 ng TEQ/kg wet weight downstream. Estimates of toxicity reference values (TRVs) derived from laboratory studies with individual PCDDs/PCDFs and PCB congeners or mixtures of those congeners, as well as application of TEFs, were compared to site-specific measures of mink exposure. Hazard quotients based on exposures expressed as concentrations of TEQs in the 95th percentile of the mink diet or liver and the no-observable-adverse-effect TRVs were determined to be 1.7 and 8.6, respectively. The resident mink survey, however, including number of mink present, morphological measures, sex ratios, population age structure, and gross and histological tissue examination, indicated no observable adverse effects. This resulted for multiple reasons: First, the exposure estimate was conservative, and second, the predominantly PCDF congener mixture present in the TR appeared to be less potent than predicted from TEQs based on dose–response comparisons. Given this, there appears to be great uncertainty in comparing the measured concentrations of TEQs at this site to TRVs derived from different congeners or congener mixtures. Based on the lack of negative outcomes for any measurement endpoints examined, including jaw lesions, a sentinel indicator of possible adverse effects, and direct measures of effects on individual mink and their population, it was concluded that current concentrations of PCDDs/PCDFs were not causing adverse effects on resident mink of the TR.

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