Sedimentary sterol levels to track river contamination by sewage in one of the largest Amazonian cities (Belém - Pará), northern Brazil

Abstract: Aim The Aurá River, located in the second-largest Brazilian Amazon city, has been experiencing the effects of human activities from riverine communities and the Aurá landfill for many years. In this study, we assess the occurrence, sources, and distribution of selected sterol markers in surface sediments of Aurá River in order to evaluate the organic matter inputs in this water body. Methods Gas chromatography-tandem mass spectrometry (GC/MS/MS) was used to identify and quantify sterol compounds. Pearson correlation, principal component analysis (PCA) and sterol ratios were used to assess sewage pollution. Results The sterol markers identified, the related diagnostic ratios, and statistical analysis showed that Aurá River sediments presented two primary sterol sources: anthropogenic (domestic sewage and inputs from Aurá landfill) and biogenic sources (terrestrial higher plants). Station 1 (the closest site to the Aurá landfill) presented the highest level of coprostanol (219.8 ng g-1). This maximum level of coprostanol and the sterol ratios indicate moderate human fecal contamination in the upper reach of the Aurá River. Coprostanol levels were similar to the lower to midrange concentrations reported for surficial river sediments around the world. Conclusions This study demonstrated that domestic sewage pollution from riverine communities and organic matter inputs from Aurá landfill might be assumed as potential threats to environmental and human health.