Avaliação de risco ecológico decorrente da presença de micropoluentes na sub-bacia hidrográfica urbanizada do rio João Mendes, Niterói RJ

Abstract

The sub-basin of the João Mendes river is one of the most important contributors to the Piratininga / Itaipu lagoon system in the Niterói oceanic region. However, it is suffering with the constant release of sewage. The Ecological Risk Assessment (ERA) is an important tool for the contaminated areas management, as it assesses the probability of occurrence of adverse ecological effects as a result of exposure to stress factors. The objective of this study was to contribute to the environmental diagnosis by assessing the ecological risks of the possible micropollutants presence in the surface waters of the rivers of the sub-basin of the João Mendes river. Four monitoring campaigns were carried out in four sampling points, one of them reference (without contamination) and three with suspected of sewage discharge contamination. The ERA model applied was proposed by Mendes, based on the Dutch Triad, which integrated chemical and ecotoxicological lines of evidence (LoE) to estimate the environmental risk of the study area. The physical-chemical parameters and a group of chemical substances of interest (CSI) were monitored by chromatography. The ecotoxicological assays that integrated the ecotoxicological LoE were: evaluation of chronic toxicity through the frequency of micronuclei in fish of the species Oreochromis niloticus (Nile Tilapia) after 5 days of exposure to surface water samples, evaluation of the inhibition of growth of the microalga Raphidocelis subcapitata after 4 days of exposure, evaluation of reproduction in microcracks of the Ceriodaphnia dubia species after 7 days of exposure to surface water samples and verification of estrogenic activity through tests performed with Saccharomyces cerevisiae yeast modified strain exposed to environmental samples of surface water after 3 days of exposure using the YES methodology. The sampling point P0 did not present a significant difference when compared to the specific controls of the ecotoxicology assays and presented low concentrations of CSI and in the physicochemical parameters. Thus, it can be used as reference point in the LoE and ERA calculation for the 3 sampling points (P1, P2 e P3). The three sampling points presented Extreme Risk (> 0.75) in all campaigns for both LoE (chemical and Ecotoxicological), as well as in Integrated Ecological Risk (P1>0.89, P2>0.88 e P3 >0.88). The highest risks were observed at the points where the highest concentrations of Bisphenol A and sulfamethoxazole occurred, being considered as some of the possible responsible for the extreme risk attributed to these points and that had in the high degree of chronic toxicity in the ecotoxicological tests.