Abstract
The presence and longitudinal and temporal distributions of the two main anionic surfactants, linear alkylbenzene sulfonates (LAS) and alkyl ethoxysulfates (AES), were monitored in surface sediments from the Guadalete estuary, located in the north of the Bay of Cadiz (SW of Spain). Seasonal samplings were performed for two years at three different stations; one of them located up-stream near the discharge outlet of a wastewater treatment plant (WWTP). A control station was also sampled in a tidal channel within the boundaries of a natural park adjacent to the estuary. LAS and AES concentration values ranged from 196 to 2864 ng g -1 and from 147 to 557 ng g -1 , respectively, the lowest values corresponding to the control station and the highest ones found near the WWTP outlet. A general decrease in the concentrations of both surfactants was found in summer, when degradation processes are faster, whereas the highest concentrations were detected during the wet months, when temperature decreases and rainwater exceeds the WWTP capacity, so untreated wastewater is discharged directly into the river. Due to differential sorption and degradation processes, the relative distribution of LAS homologues in sediments showed higher percentages for those having longer alkyl chains, whereas AES homologues with an even carbon unit number in the alkyl chain and AES ethoxymers with fewer ethylene groups were predominant. No hazard for aquatic organisms was foreseen at the concentrations found for both surfactants along the estuary.
Highlights
Significant quantities of xenobiotics reach the receiving waters despite the fact that most of the wastewaters from European cities are treated in wastewater treatment plants (WWTPs) prior to their discharge
In this paper we have focused our attention on the anionic surfactants having the largest volume of use in Europe: linear alkylbenzene sulfonates (LAS), with a production of 430000 tons per year (HERA LAS report, 2009), alkyl ethoxysulfates (AES), with a production of 276000 tons/year
LAS concentrations (Table 1) were similar to those previously reported in this area (Lara-Martín et al, 2005), in the North Sea (Bester et al, 2001) and in Japanese lakes (Inaba and Amano, 1988), but significantly lower than those found in more polluted areas on the Spanish coasts that are subjected to untreated wastewater discharges (González-Mazo et al, 1998; Petrovic et al, 2000; DelValls et al, 2002)
Summary
Significant quantities of xenobiotics reach the receiving waters despite the fact that most of the wastewaters from European cities are treated in wastewater treatment plants (WWTPs) prior to their discharge. Synthetic surfactants are included among these contaminants. They are primary cleaning agents used in laundry, cleaning and personal care products, as well as in other applications (paints, pesticides, etc). The world production of surfactants is estimated to be about 10 million tons per year (Holmberg et al, 2003), with approximately 60%. Of this amount belonging to surfactants of the anionic type (negatively charged). In this paper we have focused our attention on the anionic surfactants having the largest volume of use in Europe: linear alkylbenzene sulfonates (LAS), with a production of 430000 tons per year (HERA LAS report, 2009), alkyl ethoxysulfates (AES), with a production of 276000 tons/year
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