Relationship between genotoxicity, mutagenicity, and fish community structure in a contaminated stream

Genotoxic responses (chromosomal damage, DNA strand breakage) of redbreast sunfish (Lepomis auritis) populations exposed to industrial effluent and mutagenicity of the associated sediments were determined in order to compare them to changes in community structure. Data were collected from a reference stream and East Fork Poplar Creek (EFPC), a first-order stream which originates on the grounds of the Department of Energy Y-12 Plant at Oak Ridge, TN. This stream is contaminated with mercury, PCBs, and numerous other compounds. Previous studies have shown that sediment contaminant concentrations, as well as physiological biomarker responses of the local fish populations, are highest at the headwaters of EFPC and decrease with increasing distance from the DOE facility as contaminant loading decreases. Chromosomal damage was measured by flow cytometry – as reflected by variation in cellular DNA content – and strand breakage was determined by agarose gel electrophoresis using blood as the source of DNA. Mutagenicity was determined by the Salmonella/microsome assay using organic solvent extracts of sediment surface samples. Community level responses included community diversity and percent pollution-tolerant species. Biomarker responses and mutagenicity were found to be highest at the headwaters of EFPC, and tended to decrease with increasing distance from the effluent. In general, biomarker responses appeared to be correlated with mutagenicity of the sediment, and both of these related to fish community disturbance and level of stream contamination. Because responses at several levels of biological organization show similar patterns of downstream effects, this suggests that there may be a causal relationship between contamination and biological effects.