Disposal of dredged sediments in tropical soils: ecotoxicological evaluation based on bioassays with springtails and enchytraeids.

Metal reference values established in Brazilian legislation for terrestrial disposal of dredged sediments and soil quality were derived for temperate regions. To evaluate the adequacy of such metal reference values to tropical soils, the ecotoxicity of a dredged sediment (from the Guanabara bay, Rio de Janeiro, Brazil) was investigated in two local soils (ferralsol and chernosol) by performing avoidance and reproduction tests using Folsomia candida and Enchytraeus crypticus. Test doses consisted of 0 %, 1.25 %, 2.5 %, 5, 10 %, and 20 %. Total and potentially bioavailable metal concentrations were determined in the test mixtures. Although the chernosol mixtures had the highest total metal concentrations, the influence of the expansive clay minerals (with high ability to adsorb metals) and the high contents of nutrients typical from this type of soils, seem to reduce the ecotoxicity. Collembolan avoidance behavior was the least sensitive endpoint. The lowest sediment doses increased the reproduction of F. candida in ferralsol mixtures. E. crypticus reproduction in the ferralsol mixtures were more pronounced at lower concentrations than in chernosol mixtures. Possibly the low nutrient content of the ferralsols, in connection with the addition of small amounts of sediment, created particular conditions that promoted reproduction of the test species. Data obtained in the ecotoxicological tests may support the establishment of a "safe" ecological dose of dredged sediments to be applied in tropical soils, supporting decision-makers in programs of environmental management.