Effects of alkylphenols on the biotransformation of diuron and enzymes involved in the synthesis and clearance of sex steroids in juvenile male tilapia (Oreochromus mossambica)

Previous studies using in vivo bioassay guided fractionation indicated that the herbicide diuron (3-(3,4-dichlorophenyl)-1,1-dimethylurea) and alkylphenol (AP)-containing surfactants were detected in fractions of extracts that induced the estrogenic biomarker, vitellogenin in fish exposed to surface water extracts from the United States. However, when the compounds were evaluated individually using in vivo estrogenic assays or in vitro estrogen receptor assays, estrogenic activity was not observed. Since APs have been shown to alter activity and content of cytochrome P450s (CYP) which convert diuron to potential estrogenic metabolites, the hepatic biotransformation of diuron was measured with and without a 7 day pretreatment of p-Octylphenol (OP) and p-Nonylphenol (NP) at low (OP 13 ng/L + NP 91 ng/L), and high concentrations (OP 65 ng/L + NP 455 ng/L) in juvenile male Nile tilapia (Oreochromus niloticus). Pre-treatment with the OP/NP (AP) mixture caused elevated levels of NADPH-catal