Identification of 4-n-nonylphenol metabolic pathways and residues in aquatic organisms by HPLC and LC-MS analyses

Abstract

In order to better assess the risk associated with nonylphenol, a lipophilic contaminant of the aquatic environment having a strong tendency to bioaccumulate in organisms and exerting estrogenic effects in fish and invertebrates, we have investigated the capability of three types of freshwater species to metabolize labelled 4-n-nonylphenol. Reverse-phase radio-HPLC was used to isolate and quantify the metabolites. The identification of residues was based on co-chromatography with available standards or authentified metabolites and when possible by electro-spray ionization LC-MS analyses. The residues found in rainbow trout (Oncorhynchus mykiss), pond snails (Lymnea stagnalis) and duckweeds (Lemna minor) were identified. These freshwater organisms are able to extensively biotransform 4-n-nonylphenol. Our attempts to draw the metabolic pathways of nonylphenol evidenced oxidative attack on the alkyl chain with the production of several hydroxylated compounds and related carboxylic acids. In addition, trout and duckweeds were able to conjugate the phenol moiety to glucuronic acid and carbohydrates respectively. Traces of sulphate conjugates were also detected in trout tissues whereas no conjugate was detected in pond snails.