Ecological risk index integrating metal contamination and ecotoxicological data for estuarine sediments

This study proposes an ecological risk index (EcoRI) for metal-contaminated sediments from tropical estuaries. The EcoRI is composed of two sub-indexes: (i) chemical risk (CR), whose estimation is based on the comparison with local threshold limits, the numerical ranking of enrichment factors (EF), classes of geoaccumulation index (IGEO) and metal toxicity factors taken from the literature; and (ii) ecotoxicological risk (ER), based on bioassays with ecologically relevant organisms and the weighting of their trophic position, type of exposure (acute or chronic) and type of endpoint. EcoRI was calculated by attributing weights 1 and 2 for CR and ER, respectively, and a risk classification was proposed using four equal intervals (low, moderate, high and extreme). Secondary data from Itaipu-Piratininga Lagoon System (RJ, Brazil) was used to test the feasibility of the index. The results indicated that the lagoon system can be considered at moderate risk, and Zn, Cu, Cd and Cr were the elements that most contributed to increase CR, ER and EcoRI, especially in the canal connecting the lagoons. Hg, As and Pb were not associated with EcoRI, CR and ER, despite their known high toxicity. Increased risk scores might be associated with urbanized areas directly impacted by the discharge of domestic sewage, urban runoff and other anthropic wastes. Such areas include river mouths, the urbanized margins of the Camboatá Canal and its connections with both lagoons. Finally, EcoRI appears to be a useful tool for identifying critical areas at relevant environmental risk and key contaminants for further remediation.