Organisms in polluted areas can be exposed to complex mixtures of chemicals; however, exposure to genotoxic contaminants can be particularly devastating. DNA damage can lead to necrosis, apoptosis, or heritable mutations, and therefore has the potential to impact populations as well as individuals. Single cell gel electrophoresis, or the comet assay, is a simple and sensitive technique used to examine DNA damage. Endogenous enzymes that repair DNA can be used in conjunction with the comet assay to identify different types of DNA damage.

Three experiments were conducted with the following research objectives: 1) to determine a) if acute exposure to hexavalent chromium (Cr(VI)) would result in bioaccumulation and DNA damage in oyster (Crassostrea virginica) tissues, and b) if cellular concentrations of glutathione would affect DNA damage; 2) to determine a) if acute exposure to Cr(VI) and cadmium would cause DNA damage in sperm, b) if DNA damage affected fertilization and development rates, and c) if glutathione status affected DNA damage or reproductive success; 3) to quantify DNA strand breaks and oxidative DNA damage in isolated hemocytes from oysters (C. virginica) and clams (Mercenaria mercenaria) exposed to hydrogen peroxide and Cr(VI).

Oysters accumulated significant concentrations of chromium in body tissues after Cr(VI) exposure. The comet assay detected significant genotoxic effects in hemocytes and hepatocytes from some, but not all, Cr(VI) treatments. The toxicity of Cr(VI) in oysters appears to be influenced in part by the concentration of glutathione. Cadmium and Cr(VI) only caused DNA damage in sperm when coupled with glutathione depletion. Fertilization and development were not strongly affected by sperm exposure to Cr(VI). Exposure to cadmium resulted in slightly decreased fertilization and substantially decreased development, especially when coupled with glutathione depletion. Although hydrogen peroxide caused DNA damage in both clams and oysters, more DNA damage was observed in clams. Oxidative DNA damage was found in hydrogen peroxide exposed hemocytes of both species, but not after exposure to Cr(VI). Because DNA damage can be detected in bivalves with the comet assay, it should prove to be a useful tool for monitoring exposure to genotoxic chemicals in natural populations.