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Although the Ibirité reservoir (an urban tropical eutrophic reservoir) has been the recipient of the discharge of a large volume of raw urban sewage, the key cause of ecosystem degradation has been historically solely attributed to the discharge of effluents from an oil refinery. This fact motivated an investigation to unravel the compositions of contaminants in the sediments to evaluate their distributions, possible sources, and potential impacts on sediment–water quality. The concentrations of polycyclic aromatic and aliphatic hydrocarbons and of metals and metalloids were, in general, significantly lower than some selected polluted sites used for comparison. Calculated distribution indexes showed that the hydrocarbon sources were petrogenic, pyrogenic, and biogenic. Only a few PAHs exceeded the threshold effects level (TEL) guideline. Industrial activities are the presumed sources of metals and metalloids except for copper, which is from copper sulfate used as algaecide in the reservoir. The bioavailable concentrations of some metal and metalloid exceeded the TEL–PEL guidelines. The acid volatile sulfide concentration was greater than that of the simultaneously extracted metals in the clayey–silty reservoir sediments, whereas the opposite result was observed for the sandy sediments of the tributaries. The sediment interstitial water toxic units were >1 for metals, thus indicating that metals are potentially toxic to the benthos. Considering the data set generated in this study, it can be concluded that the degradation of Ibirité reservoir and its tributaries cannot be solely attributed to the input of hydrocarbons, but predominantly to the discharge of raw urban sewage and effluents from other industrial sources.

Toxicities of bisphenol A (BPA) and nonylphenol (NP) to the neotropical freshwater cladocerans Ceriodaphnia silvestrii and Daphnia similis were studied under laboratory conditions. Acute exposures to BPA generated mean 48-h EC values of 14.44 (6.02-22.85) mg L for C. silvestrii and 12.05 (1.73-22.37) mg L for D. similis. When the organisms were exposed to acute doses of NP, mean 48-h EC values were 0.055 (0.047-0.064) mg L (C. silvestrii) and 0.133 (0.067-0.200) mg L (D. similis). Ceriodaphnia silvestrii was also tested in chronic bioassays, which resulted in mean 8-d IC values of 2.43 (2.16-2.69) mg L BPA [no observed effect concentration (NOEC): 1.38 mg L] and 0.020 (0.015-0.026) mg L NP (NOEC: 0.015 mg L). These laboratory tests are valuable to broaden the understanding of the environmental threat posed by BPA and NP in aquatic ecosystems, and to increase the knowledge about the sensitivity of neotropical indigenous species to these contaminants. In addition to the laboratory bioassays, species sensitivity distributions were used to suggest protective concentrations of BPA and NP to prevent adverse effects on freshwater organisms. According to the obtained results, concentrations lower than 36.47 µg L BPA and 1.39 µg L NP are not expected to adversely impact aquatic organisms in natural ecosystems.

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