Ecological risk assessment and application of a preliminary mitigation strategy for the remediation of potentially toxic elements (PTEs) in a southeastern Brazilian watershed (São Carlos, SP, Brazil).

The contamination of water resources by potentially toxic species (PTEs) is a recurring problem due to rising anthropogenic activities. This study aimed to assess psollution levels and ecological risks, as well as treat surface waters in the Monjolinho watershed surface waters, located in an area of rapid and disorganized development (São Carlos, Brazil). The new HERisk software was applied to execute the ecological risk assessment, while the sample mitigation tests were performed using a mixed matrix membrane (MMM-N7) based on polyethersulfone (PES) and mesoporous material modified with amine groups (NH-MCM-41). The results revealed the presence of natural and anthropogenic enrichment sources along the watershed, such as soil lixiviation, untreated effluents dump, and agricultural runoff. The pollution indices calculated before the mitigation tests showed high water contaminations, mainly of the sampling points after the São Carlos wastewater treatment plant (WWTP). The contamination factor (CF) values found for the study region indicated extreme contamination by aluminum (Al) and manganese (Mn), whose values were 68.88 and 8.71, respectively, and high contamination by iron (Fe) and moderate contamination by barium (Ba) for the surface waters of Monjolinho, in which the respective CF values were 3.94 and 2.35. On the other side, the Água Quente stream showed the highest CF values for Ba, Mn, and Zn, which correspond to high, extreme, and moderate contamination levels, respectively, with values of 4.27, 24.27, and 1.46. Furthermore, Fe pollution along the Monjolinho River (P2 to P7) gradually increased from moderate to extreme, in which the CF and CF values were 1.42 and 7.26, respectively. Therefore, after the mitigation process using the MMM-N7, the ecological risk assessment showed that the pollution levels in the water samples dropped from extreme/high to negligible. For these reasons, the MMM-N7 shows a high potential for mitigating water systems contaminated by PTEs.