Final Report: BUI Delisting Studies in the Buffalo River AOC, 2014-2015

Abstract

Only two mink were caught during 4,157 trap-days of effort in the BR AOC during the fall of 2014. This result led to changing the focus of the study to determining mink habitat suitability and analysis of BUI chemicals of concern in mink prey. According to the USFWS Habitat Suitability Index Model, habitat in the BR AOC is poorly suited for mink. On a scale of 0 to 1, the HSI for mink is 0.38. No amphibians were observed in riparian habitats along the Buffalo River in the AOC during ~300 h of searching for them in August, October & November 2014 and April & July 2015. During 35 minnow trap-days in mid-November 2015 and ~6 h of snorkeling to overturn rocks in June and November 2015 combined, far too few crayfish to create three 70 g samples for chemical analyses were caught in the BR AOC. Lower trophic level (bluegill, pumpkin seed and yellow perch) and upper trophic level (large mouth bass) fish samples were composited and analyzed for total mercury, total PCB and total TEQ (sum of PAH REP, PCB TEQ and CDD/CDF TEQ). Among the six composited prey samples analyzed (three each of lower and upper trophic level fish) for BUI chemicals of concern, only three of the 24 analyses (4 chemicals * 6 samples) exceeded dietary LOAELs for mink: two upper trophic level fish samples for total PCB (by 8.4 and 20.1%) and one upper trophic level fish sample for PCB TEQ (by 1.4%). Mink are one of the most sensitive mammals to the chemicals analyzed, especially to TEQ concentrations of CDD/CDF and co-planar PCB congeners which have similar toxic effects. If mink living in the BR AOC ate only large mouth bass from the Buffalo River (the upper trophic level fish analyzed in this study), on average they would exceed the dietary LOAEL for total PCB by 3.6% and not exceed the dietary LOAELs for any of total mercury, PAH REP and TEQ for CDD/CDF and PCB. Since mink eat prey from multiple trophic levels, many at lower levels than large mouth bass, it is very unlikely that mink and other predatory wildlife and birds in the BR AOC are adversely affected by any of the BUI chemicals of concern. We estimated the potential dietary exposures of BR AOC mink to BUI chemicals of concern for both “worst-case” (trophic level 3.7 diet) and “typical-case” (trophic level 2.4 diet) dietary scenarios. Neither diet exceeded any of the dietary LOAELS for BUI contaminants in mink. The trophic levels of mink trapped in our previous RE AOC study, and the two mink trapped in this study, suggest that mink in the BR AOC are consuming diets with trophic levels well below that of our estimated “worst-case” diet, putting them at no increased risk for either deformities or reproductive problems. For the “Bird or Animal Deformities or Reproductive Problems” BUI, it would be reasonable to consider the delisting criteria relating to mink to be unimpaired in BR AOC because using a worst case diet scenario for mink and the analytically determined mean concentrations of BUI contaminants in potential prey a hazard assessment showed that the dietary LOAELs for the contaminants of concern would not be exceeded for mink. Because mink are highly sensitive to mercury and CDD/CDF/PCB TEQ, it is unlikely that other piscivorous wildlife and birds in the BR AOC would be adversely affected by consuming a worst-case mink diet.