Investigation of the fate of linear alkyl benzenesulfonates and coproducts in a laboratory biodegradation test by using liquid chromatography/mass spectrometry

摘要

Major coproducts of commercial mixtures of linear alkyl benzenesulfonate (LAS) surfactants are dialkyl tetralinsulfonates (OATS) and methyl-branched isomers of LAS (iso-LAS). As a total, OATS and iso-LAS can account for up to 15 of LAS. UnlikeLAS, little and contrasting information on the fate of OATS and iso-LAS is available. We have used liquid chromatography/mass spectrometry with an electrospray interface to follow biotransformation of LAS copraducts. Structure elucidation of theirbreakdown products was obtained by in-source collision-induc~d decompusition (CID) spectra. However, metabolites of LAS and iso-LAS could not be distinguished from each other by their CID spectra. According to the OECD 301 B protocol, a laboratorybiodegradation experiment of LAS end coproducts was conducted. OATS were more resistant than iso-LAS to primary biodegradation. Biotransformation of both LAS-type compounds end DATS produced, besides expected sulfophenyl alkyl monocarboxylated (SPAC) LASand sulfotetralin alkylcarhoxylated (STAC) OATS metabolites, significant amounts of dicarboxylated (SPADC and STADC) species. SPADCs were less persistent than STADCs. After more than 5 months from the beginning of the experiment, 40 and 35 of theinitial amounts of OATS and iso-LAS, respectively, were not mineralized. About 64 of refractory SPACs contained 2-5 alkanoyl carbons in the alkyl chain, while the number of alkanoyl carbons in the free alkyl chains of refractory STACs and STADCs averaged respectively 2.4 and 1.1. On the basis of the results of this study and LAS consumption, we roughly estimated that 200 000 ton of refractory organics is each year dispersed in the environment as the result of use of the above surfactants.