Investigation of sewage contamination using steroid indexes in sediments of the Guajará Estuary (Amazon coast, Brazil)

Abstract Amazonian aquatic systems are usually associated with pristine waters, however, irregular urban occupation of the hydrographic basins and sewerage deficiencies may lead to point and diffuse contamination. Sewage contamination in intertidal surface sediments from the Guajará Estuary, Brazilian Amazon coast, was evaluated using a set of steroids as biomarkers. Sediments collected along the urbanized margin were also analyzed for chlorophyll a, total organic carbon and grain sizes. Coprostanol, the main fecal sterol, was found at concentrations varying from 0.06 to 7.93 µg g-1 dry sediment, following the sequence Tucunduba > Ver-o-Peso > Porto da Palha > Tamandaré > Icoaraci > Miramar. Mixed sources of organic matter and coastal process probably concurred to produce weak correlations among the parameters. Plant derived sterols, including n-C30 alcohol and β-amyrinyl alkanoates, were clearly abundant, but they did not preclude the use of other steroid signals to the assessment of sewage contamination. High values of the steroid indexes involving 5α and 5β stanols and stanones highlighted sewage contamination at the sites with the lowest absolute coprostanol concentrations. The predominance of 5β stanols indicated a chronically sewage contamination of the area.