Histological Lesions in Mink Jaws are a Highly Sensitive Biomarker of Effect after Exposure to TCDD-like Chemicals: Field and Literature-based Confirmations

The mink (Mustela vison) is one of the most sensitive mammals to 2,3,7,8 tetrachlorodibenzo-p-dioxin (TCDD)-like chemicals. By literature review we established that a histological lesion of the jaw bone of mink, evidenced by squamous epithelial hyperplasia in the gingival tissue that forms nests or cords that infiltrate the periodontal ligament and alveolar bone causing osteolysis of the mandible and maxilla that could lead to squamous cell carcinoma, is the most sensitive known biomarker of effect following exposure of mink to TCDD-like chemicals. Lesions have been observed when total TCDD toxic equivalents (TEQ: dioxins, furans, co-planar polychlorinated biphenyls or PCBs) in liver exceed 40 ng/kg-ww or when total PCB exceeds 1,698 ng/g-ww. This is the second report of histological evidence of this lesion in wild-caught mink, and it is the first report of the lesion being grossly detectable in naturally exposed mink. Some mink living near the south shore of Lake Ontario (exposed to the lake’s food web) but not inland mink (not exposed to the lake’s food web) accumulate more than 40 ng total TEQ/kg or 2 1,698 ng total PCB/kg in liver. Because of its sensitivity, the jaw lesion biomarker is very useful for assessing the health of wildlife populations exposed to TCDD-like chemicals

Hepatic P450 Enzyme Activity, Tissue Morphology and Histology of Mink (Mustela vison) Exposed to Polychlorinated Dibenzofurans

Dose- and time-dependent effects of environmentally relevant concentrations of 2,3,7,8-tetrachlorodibenzo-p-dioxin equivalents (TEQ) of 2,3,7,8-tetrachlorodibenzofuran (TCDF), 2,3,4,7,8-pentachlorodibenzofuran (PeCDF), or a mixture of these two congeners on hepatic P450 enzyme activity and tissue morphology, including jaw histology, of adult ranch mink were determined under controlled conditions. Adult female ranch mink were fed either TCDF (0.98, 3.8, or 20 ng TEQTCDF/kg bw/day) or PeCDF (0.62, 2.2, or 9.5 ng TEQPeCDF/kg bw/day), or a mixture of TCDF and PeCDF (4.1 ng TEQTCDF/kg bw/day and 2.8 ng TEQPeCDF/kg bw/day, respectively) for 180 days. Doses used in this study were approximately eight times greater than those reported in a parallel field study. Activities of the cytochrome P450 1A enzymes, ethoxyresorufin O-deethylase (EROD) and methoxyresorufin O-deethylase (MROD) were significantly greater in livers of mink exposed to TCDF, PeCDF, and a mixture of the two congeners; however, there were no significant histological or morphological effects observed. It was determined that EROD and MROD activity can be used as sensitive biomarkers of exposure to PeCDF and TCDF in adult female mink; however, under the conditions of this study, the response of EROD/MROD induction occurred at doses that were less than those required to cause histological or morphological changes