Environmental risk assessment of a metal-contaminated area in the Tropics. Tier I: screening phase

Abstract

Purpose The present study presents data on the screening phase (tier 1) of a site-specific ecological risk assessment in a former smelter area heavily contaminated with metals (Santo Amaro, Bahia, Brazil). Joining information from three lines of evidence (LoE), chemical, ecotoxicological, and ecological, integrated risk values were calculated to rank sites within the area and identify those that may need further investigation in tier 2. Materials and methods Eleven points were selected up to 1,000 m from the smelter. Three reference points were 3 and 9 km away from the area. Risk values for the chemical LoE were derived from calculating the toxic pressure based on total metal concentrations. Those for the ecotoxicological LoE were based on avoidance (Folsomia candida and Eisenia andrei) and eluate tests (Daphnia magna acute test and Microtox) whereas for the ecological LoE the bait lamina test, soil basal respiration, and vegetation cover were used to derive risk values. Results and discussion The chemical LoE showed high risk in those points inside the area where metal loadings exceeded in much the existing soil screening values. Ecotoxicological tools showed a variable response, with tests on soil organisms inducing a higher risk (again at sites inside the smelter and with sandy soils) than tests on eluates. The three parameters composing the ecological LoE revealed a concordant response, despite the lower sensitivity of the vegetation cover. A high risk on this LoE was also observed on those sampling points where a high chemical risk was calculated. Conclusions Integrated risk was low outside the smelter area. Inside, a high spatial heterogeneity of risk levels was observed, related to the non homogeneous deposition of smelting residues. Very high risk levels, associated with sandy soils and residue deposits, suggest the need to proceed with remediation actions. However, the uncertainties associated with the contradictory information given by certain LoEs for certain sampling points show the need to confirm potential risks in a tier 2 analysis.