Metabolite Production during the Biodegradation of the Surfactant Sodium Dodecyltriethoxy Sulphate under Mixed-culture Die-away Conditions

1 Department of Biochemistry, University College Cardiff, PO Box 78, Cardiff CF1 1XL, UK 2 Unilever Research Port Sunlight Laboratory, Wirral, Merseyside L63 3JW, UK ABSTRACT Summary: Sodium dodecyltriethoxy sulphate (SDTES), either pure or as a component of commercial surfactant mixtures, underwent rapid primary biodegradation by mixed bacterial cultures in OECD screen and river-water die-away tests. Inoculation of [ 35 S]SDTES-containing solutions with OECD screen test media acclimatized to surfactants or their degradation products led to production of various 35 S-labelled glycol sulphates and their oxidation products, all known to occur during degradation of [ 35 S]SDTES by pure bacterial isolates. Triethylene glycol monosulphate was the major catabolite together with smaller amounts of di- and monoethylene glycol monosulphates implying, by analogy with pure cultures, that ether-cleavage was the major primary biodegradation step. The oxidation product (carboxylate derivative) of each glycol sulphate was also detected together with metabolites tentatively identified as -/β-oxidation products of the dodecyl chain. Relatively little SO 4 2- was liberated directly from SDTES but mixed cultures derived from sewage could metabolize the sulphated glycols to SO 4 2- . The environmental relevance of these degradation routes was established by following metabolite production from [ 35 S]SDTES in full-scale river-water die-away tests. Triethylene glycol sulphate was formed first, then rapidly oxidized to acetic acid 2-(diethoxy sulphate) which persisted as the major metabolite for 2–3 weeks. Small amounts of sulphated derivatives of di- and monoethylene glycols were also detected during the same period. Very little SO 4 2- was formed directly from SDTES but large amounts accompanied the eventual disappearance of glycol sulphate derivatives. None of the 35 S-labelled organic metabolites was persistent and, whenever [ 35 S]SDTES was a component of a commercial mixture, all ester sulphate was completely mineralized to 35 SO 4 2- within 28 d. Present address: Department of Biochemistry and Agricultural Biochemistry, University College Aberystwyth, PO Box 2, Aberystwyth SY23 2AX, UK.