Fate and distribution of linear alkylbenzene sulfonates in the littoral environment

A study was conducted of the fate and behavior of LAS in a shallow coastal zone adjoining the Bay of Cadiz (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.