Thumbnail Image

Adaptive Tolerance to Zinc in Freshwater Snails (Physa acuta) Across a Contamination Gradient

Hickey, Joel
The Tri-State-Mining district is an area of northeast Oklahoma, southwest Missouri, and southeast Kansas in which zinc and lead mines operated for over 100 years. Metal contamination from wastes left behind by these historic mining operations has polluted the Neosho and Spring Rivers, the Grand Lake o' the Cherokees, and resulted in the EPA designating Tar Creek a superfund site in 1983. The receiving watershed has a gradient of contamination from likely toxic concentrations of zinc to background concentrations. The purpose of this study was to determine if native populations of freshwater snails have developed tolerance to environmental metal concentrations and, if present, the extent of the metals tolerance across a downstream gradient from the metals-contaminated area. Snails (Physa acuta) were collected from sites representing the gradient of metals contamination and field sediment and water samples were analyzed for zinc. These populations were cultured in the lab and zinc toxicity tests were conducted with F1+ juveniles collected from those cultures. Snails cultured from populations collected from contaminated, upstream sites were more tolerant to zinc exposure than snails cultured from populations collected from clean, downstream sites. Additionally, zinc tolerance was found in snails collected from a site that represented a midpoint geographically, although environmental zinc levels were below levels likely to cause toxicity. My results suggest that, despite past studies showing sediments from Grand Lake to be relatively nontoxic to sediment-dwelling organisms due to low bioavailability; aquatic organisms may still be experiencing physiological stress and selective pressures because of metals contamination.