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

Major coproducts of commercial mixtures of linear alkyl benzenesulfonate (LAS) surfactants are dialkyl tetralin-sulfonates (DATS) and methyl-branched isomers of LAS (iso-LAS). As a total, DATS and iso-LAS can account: for up to 15% of LAS. Unlike LAS, 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 coproducts. Structure elucidation of their breakdown products was obtained by in-source collision-induced decomposition (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 laboratory biodegradation experiment of LAS and coproducts was conducted. OATS were more resistant than iso-LAS. to primary biodegradation. Biotransformation of both LAS-type compounds and DATS produced, besides expected sulfophenyl alkyl monocarboxylated (SPAC) LAS and sulfoletralin alkylcarboxylated (STAC) DATS 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 the initial 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.