Metabolic fate of 2,4-dichloroaniline, prochloraz and nonylphenol diethoxylate in rainbow trout: a comparative in vivo/in vitro approach.

The metabolism and distribution of 2,4-dichloroaniline (2,4-DCA), prochloraz and 4-n-nonylphenol diethoxylate (NP2EO) were investigated in vivo and in vitro in rainbow trout (Oncorhynchus mykiss). Each compound was administered p.o. (10 mg/kg wet weight) and urine was collected during 48 h (2,4-DCA, prochloraz) or 72 h (NP2EO). Fish were sacrificed, the gall bladder was excised and radioactivity was measured in tissues, viscera and carcasses. Metabolic profiles were performed by radio-HPLC and when possible metabolites were identified by LC/MS. For comparison, the biotransformation of these xenobiotics was also investigated in freshly isolated hepatocytes. The metabolic pathways of 2,4-DCA have been identified leading to the glucuronide conjugate (in vivo) and to the glucuronide conjugate and the hydroxylamine metabolite (in vitro). This difference highlights the usefulness of the hepatocyte system in metabolic studies, since the formation of the hydroxylamine reactive metabolite cannot be demonstrated in vivo. For prochloraz, we observed that residue levels are significantly higher in males than in females for gill, fat, brain and carcasses, however, the reasons for this difference remain unclear. Although, the presence of glucuronide conjugates was detected in vivo and in vitro, the chemical structure of isolated metabolites has to be determined. However, the comparison of the in vivo versus in vitro metabolic profiles indicates that several peaks, probably corresponding to intermediate metabolites, were present only in hepatocyte incubations. Biotransformation of NP2EO occurred in vivo and in vitro in rainbow trout, but did not result in the formation of 4-n-NP. The major metabolite present in bile corresponded to the NP2EO-glucuronide but this metabolite was not found in vitro. It is concluded that hepatocytes may produce a different metabolic pattern than in the whole fish, but may also give evidence of a metabolic pathway difficult to apprehend in vivo.