Linear alkylbenzene sulfonates (LAS) as tracers of urban waste waters in shallow littoral ecosystems: A case study in the Bay of Cádiz

Abstract

The spatial distribution of linear alkylbenzene sulfonates (LAS) and their composition of homologues in sediments of Cádiz Bay, a semienclosed system surrounded by urbanized areas, has been studied. LAS homologues were measured in marine sediments using solid-phase extraction and reversed-phase high-perfomance liquid chromatography with spectrofluorimetric detection. Results showed that LAS, principally associated with solids in suspension and originating from the existing outlet where urban waste waters are discharged into the Sancti Petri Channel, are transported to Cádiz Bay during the ebb tide or emptying phase. The transport of solids in suspension is defined by the circulation of tidal currents and its sedimentation will be encouraged in those zones where the water has a long residence time, zones of low energy, where the accumulation of the surfactant takes place. These results enable the area of influence of the urban waste water discharge to be determined. The distribution of the various LAS homologues in the sediment samples is different from that of the commercial LAS. The greater the distance from the discharge point, the smaller the quantities of the long-chain homologues.