The city of Belém of Pará, its surroundings and body waters are subject to environmental impacts due to the increase of local population and poor sanitation conditions. The Guajará bay receives untreated sewage effluents from Belem’s catchment area, which is of concern to public health and environmental quality. This study aimed to identify organic contamination in surface sediments and sediment cores of the Guajará estuary using steroids as biomarkers. Steroids have been used since 1960 as tracers of natural and anthropogenic organics in the aquatic environment, however, studies using such compounds in the northern region of Brazil is new. Therefore data from other regions were important for comparison and to improve our knowledge about the composition of organic matter in the Guajará Bay. Samples of surface sediments and sediments cores (~50 cm) were collected in January 2011. The sediments cores were taken from Tucunduba, Icoaraci. Surface sediments were collected in Tamandaré, Porto da Palha, Ver-o-Peso, and Miramar. Steroid analyses were performed using gas chromatography with flame ionization detection. Sediments were subsampled for analysis of chlorophyll, total organic carbon and grain size. Several steroids were identified (coprostanol, cholesterol, epicoprostanol, colestanol, colestanona, coprostanona, estigmasterol, brassicasterol, β-sitosterol, β-sitostanol), from both natural and anthropogenic sources. Concentrations of coprostanol, an sterol of fecal origin, in surface samples ranged from 0.06 to 5.61μg g-1 and in the sediments cores of Tucunduba, 0.02 to 11.23 μg g-1 and Icoaraci 0.03 of 0.31 μg g-1. For the surface sediment samples, highest coprostanol concentrations were observed at Ver-o-Peso, in contrast to the high sand content of the sediments. For the sediment cores, two different profiles were observed: for Tucunduba the steroids that predominated at high concentrations within the top layers were coprostanol, coprostanona, colesterol e colestanol, which indicated recent sewage inputs. For Icoaraci, brassicasterol, estigmasterol, sitosterol e sitostanol, steroids of plant sources predominated at higher concentrations. Absolute coprostanol concentrations and steroid concentration ratios indicated that most of the sampling sites were contaminated by untreated sewage. The use of steroid ratios to understand the results was also important to minimize the dependence of the steroids to organic carbon content and granulometry.
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