DISPOSIÇÃO TERRESTRE DE SEDIMENTOS DE DRAGAGEM: ECOTOXICIDADE, BIODISPONIBILIDADE DE METAIS E ESTUDO DE CASO EM BELFORD ROXO (RJ)

The ecotoxicity and bioavailability levels of metals associated with terrestrial disposal of dredged sediments were studied using acute bioassays with earthworms (Eisenia andrei) and aquatic micro-crustaceans (Daphnia similis). A sample of dredged sediment (from domestic wastes-contaminated rivers and disposed on an Environmental Protection Area at the Belford Roxo Municipality) was collected. The characterization of the sediment involved the determination of texture, pH, organic matter, clay minerals and metals (mercury, lead, chromium, nickel, zinc and cooper). The bioassays with earthworms was performed with mixtures of artificial soil:sediment, according to the following proportions: 0, 6, 12, 24, 50 and 100%. The assay with D. similis was conducted using a leachate of the sediment, which was diluted for the same proportions used for earthworms. Chromium was the only metal whose concentration was higher than the limit established by Brazilian law. The bioassays with earthworms revealed low levels of toxicity, in agreement with low contents of lead, nickel, chromium and mercury found in tissues of surviving organisms. In this respect, high organic matter contents (~7%) and the presence of expansive clay mineral (smectite) in the sediment might have promoted the complexation of metals, reducing their bioavailability. Also, the earthworms apparently recognized the organic matter from the sediment as source of food. All test concentrations provoked significant effects on D. similis, indicating high toxicity (possibly associated with the acidity of the sediment; pH~3). In conclusion, this sediment exhibited low toxicity levels for earthworms. On the other hand, leachates of this sediment may impact surrounding fluvial ecosystems. Key-words: Earthworms, micro-crustaceans, bioassays, metals, dredged sediments.