Oxidative metabolism of chlorinated paraffins by freshwater fish liver microsomes: Major metabolites detected in marketable freshwater fish.

The emerging environmental pollutant class of chlorinated paraffins (CPs) has garnered increasing concern in recent years. The oxidative metabolism of CPs by fish is an important pathway for the degradation of CPs present in aquatic ecosystems. However, the factors affecting the oxidative metabolism of CPs by fish are poorly understood, with only a few studies having examined CP metabolites in fish; research that focuses on fish from the natural environment is even more scarce. In the present study, single and mixed CP standards were incubated in vitro with fish liver microsomes to study the formation of CP metabolites. In addition, the presence of CPs and associated metabolites were analyzed in marketable freshwater fish. The in vitro fish liver microsome experiments showed the metabolic elimination ratio of short-chain CPs ≈ medium-chain CPs > long-chain CPs. Both mono- and di-hydroxylated oxidative metabolites of CPs were identified. Importantly, although both monohydroxylated CPs (monoOH-CPs) and CP ethers were detected in the tested marketable fish, only monoOH-CPs were confirmed as oxidative metabolites of CPs; moreover, a large amount of false positive C14H24Cl6 was detected. This study provides valuable insights into the biotransformation of CPs in fish. The results highlight the importance of chromatographic separation when analyzing CPs and associated metabolites in fish. Further, assessments of the ecological/health risks of CPs should pay special attention to monoOH-CPs since these species may have higher toxicities than the parent compounds.