POTENCIAL TÓXICO DE SEDIMENTOS DRAGADOS DAS BAÍAS DE SEPETIBA E DA GUANABARA (RJ) EM CENÁRIO DE DISPOSIÇÃO EM LATOSSOLO

Potential toxicity of dreged sediments from Sepetiba and Guanabara bays (RJ) in scenario of disposal in ferrasols

Abstract

Inadequate discharges of domestic and industrial wastes have degraded estuarine ecosystems from Rio de Janeiro State (RJ). Dredging operations are often required to restore these environments and, because of that, the evaluation of potential toxicity of dredged materials in soils has become important. This work proposes the ecotoxicological evaluation of dredged sediments from the mouth of Saco do Engenho (Sepetiba bay, RJ), Meriti River (Guanabara bay, RJ) and Sao Francisco Channel (Sepetiba bay, RJ) in scenario of disposal in ferralsols. Metal concentrations in sediments were determined by ICP-OES, and metal enrichment factors (FE) were also estimated. The doses of sediment applied onto soils varied between 0 and 40%, where 0% = pure ferralsol. Acute bioassays with earthworms (Eisenia andrei) were performed in mixtures of soil:sediment according to standard protocol (ASTM). Median lethal concentration on 50% of the organisms (CL50), expressed in % of sediment mixed with soil, was estimated through PriProbit analysis. Metal concentrations in the sediments were above the limits established by Brazilian law (CONAMA 454 & 420) for disposal of dredged sediments in aquatic environments and soil, except for the sediment collected in the São Francisco channel, whose metal contents are in agreement for land disposal. The highest toxicity level was found for the sediment from the Saco do Engenho (CL50 = 13.06%), followed by Meriti River (CL50 = 14.60%) and São Francisco channel (CL50 = 28.02%). Such data seem to support metal concentrations determined in the sediments, whose highest concentrations were found for the Saco do Engenho, followed by Meriti River. In addition, the values of metal-enrichment factors suggest the occurrence of important metal anthropogenic sources for the sediments from Saco do Engenho and Meriti River. Finally, the sediments were toxic to the earthworms and the threshold limits established by Brazilian legislation should be revised taking into consideration the properties of the main Brazilian pedological occurrences.