Determination and distribution of alkyl ethoxysulfates and linear alkylbenzene sulfonates in coastal marine sediments from the Bay of Cadiz (southwest of Spain)

Abstract

The distribution of the two main anionic surfactants manufactured and used in the world, alkyl ethoxysulfates (AES) and linear alkylbenzene sulfonates (LAS), has been studied in sediments from a salt marsh and an estuary of the Bay of Cadiz (southwest of Spain). The identification and quantification of AES and LAS was carried out after automated Soxhlet extraction with methanol, followed by solid-phase extraction and liquid chromatography coupled to electrospray mass spectrometry. The latter procedure permitted the unequivocal identification of every LAS homologue as well as the AES homologues of up to 16 carbon atoms in their alkyl chain and of up to 12 ethylene oxide groups. Recoveries were in the range of 51% to 84% and limits of detection from 1 to 5 microg/kg. We have focused our attention particularly on AES because, in spite of their great use, these compounds have received less attention than LAS and their occurrence has not been described in marine environmental samples. Alkyl ethoxysulfates concentration values range between 100 and 400 microg/kg in the topmost layer of sediments at the sampling areas. The relative distribution of AES homologues shows higher percentages for the longer alkyl chain homologues in sediments as well as for the shorter ethoxymers. A decrease in LAS concentrations has been found relative to past studies in one of the sampling areas as a consequence of the reduction of urban wastewater discharges.