Characterization of Recalcitrant Intermediates from Biotransformation of the Branched Alkyl Side Chain of Nonylphenol Ethoxylate Surfactants

Abstract

Nonylphenol polyethoxylates (A9PEs) are complex mixtures of isomers and oligomers widely used as surfactants. The weakly estrogenic effects of the A9PE breakdown products are impelling reformulation of many commercial products and have made “A9PE free” products an industry trend. Initial A9PE biotransformation is known to produce metabolites with shortened ethoxy chains, mainly A9PE2, and carboxylated ethoxy chains, mainly A9PE2C. Very little is known on the ultimate fate of the branched alkyl side chain. We have used liquid chroma tography−electrospray−mass spectrometry to elucidate structures of species generated from biotransformation of the branched alkyl chain. According to an OECD protocol, a laboratory A9PE biodegradation experiment was conducted. After about two weeks from the beginning of the experiment, relevant amounts of species having both side chains oxidized (CAPECs) and 3−8 carbons in the residual alkyl chain appeared in the test solution. These species were presumably generated from less extensively alkyl branched A9PEC isomers by various oxidative mechanisms. The unreacted most extensively alkyl branched A9PEC isomers disappeared from the test liquor after more than 3 months by an unknown mechanism. Less abundant, metabolites having only the alkyl chain carboxylated (CAPEs) were also formed. With time, these species were slowly transformed to CAPECs. Apart from a very slow conversion of CAPE2Cs to CAPE1Cs, this metabolite class was extremely recalcitrant to further biotransformation, as they persisted in the test liquor even more than 5 months after their generation. Analysis of a sewage treatment plant effluent showed CAPECs, as a total, were present at concentration of 58 μg/L, accounting for 63% of the total A9PE metabolites leaving the plant.