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The distribution of linear alkylbenzene sulfonates (LAS) and their biodegradation intermediates (SPC) has been studied at a salt marsh of the Bay of Cadiz. The identification and quantification of LAS and SPC was carried out after solidphase extraction of 250 mL of water samples followed by liquid chromatography with fluorescence, diode array, and ionspray mass spectrometry. The latter procedure permitted the unequivocal confirmation of long-chain SPC, of up to 11 carbon atoms in seawater, and of up to 13 carbon atoms in interstitial water. Some of these compounds have not been described until now in environmental samples. The relative abundance of the SPC found at some of the sampling stations agrees with what would be expected after the occurrence of the first and second β-oxidations of the alkyl chain of the various homologues of commercial LAS. Furthermore, the existence of SPC-C13 in interstitial water proves unequivocally that ω-oxidation occurs in the environment. In general terms, the persistence of longchain SPC is evidence that the biodegradation of LAS is a slow process in a marine environment that is deficient in oxygen and highly contaminated with other organic substrates.

A study was conducted of the fate and behavior of LAS in a shallow coastal zone adjoining the Bay of Ca ´diz (southwest of Spain). The area is subjected to strong tidal currents and receives directly the discharge of untreated wastewaters of a population of about 100 000 inhabitants. LAS showed a nonconservative behavior due to intense biodegradation and due to sorption and settling of material in suspension. The sorption to suspended matter affects the way in which its dispersion takes place in zones with high turbidity, since this fraction may represent up to 60% of the total quantity present in the medium. The surfactant character of LAS is also illustrated by a strong sorption at the water-atmosphere interface. In zones close to urban effluent discharge points, this translates into a steep vertical gradient in the LAS concentration, with values found in the top 3-5 mm of water depth some 2 orders of magnitude greater than those found at a depth of 0.5 m. Over a large part of the area studied, the LAS concentration in the sediment and in the water column can be described by means of the Freundlich's equation.

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