Temporal variation of sewage contamination of a tropical and highly urbanized estuary

The Capibaribe Estuarine System (CES, NE Brazil) is an ecosystem of ecological and socioeconomic relevance but undergoes intense degradation from anthropogenic activities, especially sewage dumping. This study evaluated contamination by linear alkylbenzene sulfonates (LASs) in water and linear alkylbenzenes (LABs) in sediments at seven stations in the CES during the dry and rainy seasons. The LAS concentrations ranged from 0.05-1.53 mg L-1 (median of 0.12 mg L-1), exceeding the Brazilian legal limit of 0.2 mg L-1 and the predicted no effect concentration of 0.031 mg L-1 for marine organisms, indicating a potential risk to aquatic organisms. Effluent outflow from sewage treatment plants (STPs) was higher during the rainy season, resulting in a tendency for increased LAS concentration in the surface estuarine waters. Most sediments showed moderate LAB contamination (200-2000 ng g-1) in both seasons, with an exception observed near an STP, during the rainy season. In the dry season, LAB spatial distribution was mainly regulated by the proximity of sewage sources, whereas in the rainy season, sediment grain size was an important factor. Linear alkylbenzene degradation did not vary seasonally due to high temperatures and the net heterotrophic conditions of the environment, which favor degradation year round. The highest LAS and LAB concentrations were recorded in the middle estuary, the area most affected by sewage and with high turbidity. The data indicates the need for special attention from environmental authorities and will support effective management plans to mitigate current and future pollution.