Hepatic micronuclei in brown bullheads (Ameiurus nebulosus) as a biomarkerfor exposure to genotoxic chemicals

In order to test whether an in vivo technique for detecting hepatic micronu clei in teleosts can be used as a biomarker for exposure to genotoxic chemi cals in the aquatic environment, the frequencies of hepatic micronuclei wer e determined in brown bullheads (Ameiurus nebulosus) from two contaminated sires (Hamilton Harbour. Black River) and two reference sites (Bay of Quint e, Old Woman Creek) in Lake Ontario and Lake Erie, respectively. Micronucle i were enumerated in the hepatocytes of fish with and without prior exposur e to a hepatic necrogen, allyl formate; which was previously shown to stimu late regenerational proliferation of hepatocytes in an in vivo trout model. Bullheads collected in the spring from the Black River had mean hepatic mi cronucleus frequencies of 1.0 and 0.41 per 1,000 hepatocytes in treatments with and without allyl formate, respectively, which was significantly great er than the mean frequencies of 0.1 and 0 micronuclei per 1,000 hepatocytes in bullheads collected in the spring from the Old Woman Creek reference si te in treatments with and without allyl formate, respectively. No micronucl ei were observed in bullheads collected in the fall from Hamilton Harbour a nd the Bay of Quinte in rests with and without allyl formate. Elevated numb ers of binucleated hepatocytes in bullheads from the Black River and Hamilt on Harbour that were not injected with allyl formate indicated enhanced reg enerational proliferation of liver tissue in fish from contaminated sites. These data indicate that monitoring of micronuclei in teleost hepatocytes h as potential as an in situ biomarker for genotoxic contaminants but this as say may not be sufficiently sensitive to detect exposures in moderately con taminated locations. The lack of hepatic micronuclei in bullheads collected in the fall from the Hamilton Harbour and the Bay of Quinte sites may indi cate seasonal differences in responses.