Surfactants in sediment of Itanhaém Estuary,São Paulo,Brazil

This study investigated surfactant levels in the sediment of Itanhaém Estuary through colorimetric methods with methylene blue active substances (MBAS). Samples were collected with a Van Veen bottom sampler at eight sampling points during autumn, winter, and spring of 2015. The results demonstrate growing detergent deposition in the sediment of the estuary. Surfactant concentration was higher (16.18 μg MBAS g⁻¹) around the sewage treatment plant (STP) than in the estuary in autumn, after the vacation/summer season when the population of the city had increased due to tourism. There was a significant (p < 0.05) reduction in detergent concentration (to 14.94 μg MBAS g⁻¹) in winter, after school vacation, while in spring the surfactants concentration for the STP was high only for the sampling points nearer the ocean. Surfactant concentrations differed significantly among sampling points (p < 0.05), with them being higher at those closer to the STP. Enrichment with high loads from anthropogenic sources associated with urbanization and tourism was responsible for the greater surfactant concentrations in areas near the STP. In conclusion, more efficient treatment of domestic effluent of the city of Itanhaém is needed, as is the control of clandestine discharge into the river since the accumulation of detergents in sediment can have harmful effects on aquatic life.