Genotoxicity of a polluted river system measured using the alkaline comet assay on fish and earthworm tissues

Monitoring genotoxicity in the environment by using endemic organisms as sentinels requires sensitive assays. In this study the genotoxic properties of water and sediment collected from the Noyyal River, which is polluted with industrial effluent and sewage, was determined in fish (Cyprinus carpio) and earthworms (Eisenia foetida) using the alkaline comet assay. Upon electrophoresis, extensive DNA damage, measured as the DNA length:width ratio of the DNA mass, was observed in erythrocytes, liver, and kidney cells of fish exposed to polluted water samples and the amount of damage increased with the duration of exposure. Similarly, the mean DNA length:width ratio was significantly higher in the coelomocytes of earthworms placed in sediment samples. The highest levels of DNA damage were obtained with samples taken at and immediately downstream of urban centers. The results of this study indicate that the Noyyal River system is contaminated with substances that are genotoxic to fish and earthworms and that the comet assay has sufficient sensitivity to detect the genotoxicity.