Accumulation of cis and trans chlordane by channel catfish during dietary exposure

Abstract

Although chlordane is no longer in commercial use, residues of this complex mixture organochlorine insecticide in fish remain common. Accumulation of chlordane in the liver and muscle of the channel catfish (Ictalurus punctatus) was investigated through both multi-dose 28 day dietary exposures and a single-dose time course experiment in which both uptake and elimination were followed. Chlordane concentrations were also evaluated in channel catfish from an urban estuary. The cis isomer accumulated preferentially to the trans isomer in both liver and muscle tissues, and the cis to trans ratio generally exceeded the corresponding ratio in the spiked feed, suggesting a relative resistance to metabolism and/or excretion. The cis to trans ratio was three times greater in the wild fish than in the laboratory exposed fish. Although detected at low concentrations (relative to parent compounds) in the muscle and liver tissues of the wild fish, oxychlordane, a metabolite readily accumulated by mammals, was not detected in either tissue during any of the laboratory exposures. Elimination of the chlordane isomers from both liver and muscle was biphasic. In both tissues, the slow phase elimination constant (K_e) for trans-chlordane was 2–4 times that for cis-chlordane. Collectively, our results suggest that slower metabolism and/or excretion of the cis isomer relative to the trans isomer lead to the preferential accumulation of cis-chlordane in aquatic biota. Additionally, the presence of oxychlordane in channel catfish tissue may be due to direct exposure, rather than metabolism of parent compounds by the fish.