Occurrence and fate of selected surfactants in seawater at the outfall of the Marseille urban sewerage system

This paper describes an investigation of linear alkylbenzene sulfonates (LAS) and nonylphenol ethoxylates (NPEO) and their metabolites in the vicinity of the Marseille sewage outfall (wastewater treatment plant with a capacity of 1.860 million inhabitant equivalents, Northwestern Mediterranean, southeast of France). This analytical survey describes their occurrence in the subsurface and sea surface layers and investigates their possible fates in this marine environment. The results indicated the presence of LAS in both layers and up to 3 km from the discharge point, whereas the concentration of sulfophenyl carboxylic acids, which are the main metabolites of LAS, was only significant near the sewer outfall and in the surface layer. The NPEO were present only in minor quantities, especially near the discharge point, and no other selected metabolites were detected. The fate of the surfactants in question was then assessed by two types of experiments according to their potential means of degradation under natural conditions. Biodegradation assays were conducted according to a protocol defined by the United States Environmental Protection Agency (“Biodegradability in sea water, 835.3160”), with variations in the substrate input frequencies. Photodegradation experiments were carried out in a solar simulator reactor. These results demonstrated the low photodegradability and rapid primary biodegradation of LAS (with half-life times between 10.3 and 11.5 days) in the coastal area under study, although some LAS metabolites were more recalcitrant to biodegradation in this specific environment, which was also validated by linear alkylbenzene analysis in the two selected sediment stations.