Hepatic Micronuclei in Brown Bullheads ( Ameiurus nebulosus) as a Biomarker for Exposure to Genotoxic Chemicals

Abstract

In order to test whether an in vivo technique for detecting hepatic micronuclei in teleosts can be used as a biomarker for exposure to genotoxic chemicals in the aquatic environment, the frequencies of hepatic micronuclei were determined in brown bullheads ( Ameiurus nebulosus) from two contaminated sites (Hamilton Harbour, Black River) and two reference sites (Bay of Quinte, Old Woman Creek) in Lake Ontario and Lake Erie, respectively. Micronuclei were enumerated in the hepatocytes of fish with and without prior exposure to a hepatic necrogen, allyl formate; which was previously shown to stimulate regenerational proliferation of hepatocytes in an in vivo trout model. Bullheads collected in the spring from the Black River had mean hepatic micronucleus frequencies of 1.0 and 0.41 per 1,000 hepatocytes in treatments with and without allyl formate, respectively, which was significantly greater 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 site in treatments with and without allyl formate, respectively. No micronuclei were observed in bullheads collected in the fall from Hamilton Harbour and the Bay of Quinte in tests with and without allyl formate. Elevated numbers of binucleated hepatocytes in bullheads from the Black River and Hamilton Harbour that were not injected with allyl formate indicated enhanced regenerational proliferation of liver tissue in fish from contaminated sites. These data indicate that monitoring of micronuclei in teleost hepatocytes has potential as an in situ biomarker for genotoxic contaminants but this assay may not be sufficiently sensitive to detect exposures in moderately contaminated locations. The lack of hepatic micronuclei in bullheads collected in the fall from the Hamilton Harbour and the Bay of Quinte sites may indicate seasonal differences in responses.