Ecological risk index for aquatic pollution control: a case study of coastal water bodies from the Rio de Janeiro State, southeastern Brazil

Abstract

The Potential Ecological Risk Index (PERI) was proposed by Hakan- son in 1980 to be used as a diagnostic tool for water pollution. The aim of this study was to apply the PERI for tropical conditions, proposing modifications. The metal contamination of 15 areas, including five bays, from the coastal systems of the Rio de Janeiro State, Brazil, which pre- sent different pollution degrees and trophic status, was assessed. For environment sensitivity assessment through bioproduction estimation, the ratio of total phosphorus (in mg/g)/organic matter in sediment (in %) ×100 was used, instead of the correlation between total nitrogen and organic matter as used in the original index calculation. The results for environment sensitivity were correlated with the concentration of acid volatile sulfides in sediments and with chlorophyll-a of the water column, showing a compatible relationship between water trophic status and se- diment anoxia. The highest degree of contamination (DC) was found for the N-NW sector of the Guanabara bay (60.21 – classified as very high), followed by the Sepetiba bay stations, which showed DC values classified as moderate. The Ilha Grande bay and Paraty (Mamangua) showed low DC values. The station of the Guanabara bay was the only one classified by the index as of very high ecological risk (PERI=697), followed by three stations classified as of moderate risk (Mouth of Guanabara bay; Garsas, Sepetiba bay; and Angra, Ribeira bay). All the other stations present low risk associated with metal exposure. As mercury is the metal of highest toxicity factor in the Hakanson formulation, a control test was applied to observe the relationship between PERI and mercury concentrations in fish and its bioconcentration factors, which are related to mercury bioavailability in the system. The results of the modified PERI were fully satisfactory for ranking areas of contamination. Keywords: coastal systems, toxic metals, trophic status, sediments, fish.