Fate of linear alkyl benzenesulfonates, coproducts, and their metabolites in sewage treatment plants and in receiving river waters

While much attention has been paid to assess contamination levels of linear alkyl benzenesulfonate (LAS) surfactants in the environment, only a few papers have reported on the levels of breakdown products of LAS and coproducts. Major LAS coproducts are dialkyl tetralinsulfonates (DATS) and methyl-branched isomers of LAS (iso-LAS). A previous method (accompanying paper) based on solid-phase extraction (SPE) and liquid chromatography/mass spectrometry has been modified for monitoring the above analytes in aqueous samples of sewage treatment plants (STPs) and in river waters. Analytes were extracted from 25, 200, and 1000 mt of respectively raw sewage, treated sewage, and river water samples by a 0.5-g Carbograph 4 SPE cartridge. Recovery studies of some authentic short-chain LAS metabolites suggested that the SPE cartridge was able to quantitatively extract all the compounds of interest from the three types of aqueous matrixes. Under full-scan conditions, limits of detection of the method for metabolites of LAS and coproducts was set at 2 ng/L in river water. By this procedure, the concentrations in water of the analytes entering and leaving five activated sludge STPs were monthly monitored over several months. Field data indicated that about 50% of the metabolites of LAS coproducts were not mineralized by activated sludge treatment. More than 12% of them were dicarboxylated species. On the average, DATS metabolites amounted to more than 50% of the total analyte concentrations in STP effluents. A short survey of the fate of persistent metabolites of LAS coproducts discharged from a STP in river water gave us some evidence that iso-LAS metabolites continued to degrade in the aquatic environment.