Bioaccumulation of chlordane by channel catfish (Ictalurus punctatus) and toxicity to a human liver epithelial cell line

Abstract

Although chlordane is no longer in commercial use, residues of this complex mixture organochlorine insecticide remain common. Its bioaccumulation in channel catfish (Ictalurus punctatus) was investigated through multi-dose 28 day dietary exposures and a single-dose time course experiment. Chlordane residues were also measured in channel catfish from an urban estuary. Laboratory exposures demonstrated a preferential accumulation of cis over trans-chlordane in both liver and muscle tissues, which was amplified in the wild fish. Oxychlordane, a metabolite readily accumulated by mammals, was not detected in either tissue during any of the laboratory exposures. Its presence at low concentrations (relative to parent compounds) in both muscle and liver tissue of wild channel catfish appears to be due to direct exposure, rather than chlordane metabolism by the fish. Hepatic cytochrome P-450 activity was verified in both hatchery-raised juvenile channel catfish and adult wild fish. The recognition of by scup monoclonal antibody (MAb 1-12-3) of an hepatic microsomal protein in channel catfish, which is enhanced by benzo-a-pyrene (BaP) exposure and coincident with induction of 7-ethoxyresorufin-o-deethylase (EROD) activity, confirmed the presence of the CYP1A protein. EROD activity and CYP1A protein were also enhanced in adult channel catfish from an urban water body, the sediments of which contain elevated levels of some polynuclear aromatic hydrocarbons including BaP. Technical chlordane, the pure cis and trans isomers, heptachlor epoxide and oxychlordane, were evaluated for toxicity to a human liver epithelial cell line. Chlordane isomer-metabolite mixtures representative of chlordane residues in the tissue of wild fish were also tested. Only slight differences in toxicity were observed among the individual compounds, with heptachlor epoxide being the least toxic. The isomer-metabolite combinations proved additive in their cytotoxicity. Although the cytotoxicity data presented for immortalized human liver epithelial cells indicates that the chlordane isomers and oxychlordane are additive in their effects on cell metabolism, additional research is necessary in order to judge the relevance of these findings with regard to chlordane's mammalian hepatotoxicity.