Disposal of dredged sediments in tropical soils: metal ecological risk assessment based on bioassays with aquatic and edaphic organisms

Potential ecotoxicity associated with the disposal of dredged sediments (from the Guanabara Bay, Rio de Janeiro, Brazil) in ferralsols and chernosols was studied through acute bioassays with microcrustaceans (Daphnia similis) and earthworms (Eisenia andrei); and through chronic assays with algae (Pseudokirchenriella subcaptata). Total metal concentrations in the sediment were higher than the limits established by Brazilian legislation for dredged sediment disposal. The bioassays suggest the occurrence of more significant effects on ferralsols mixtures compared to chernosols treatments. In chernosol mixtures, the abundance of 2: 1 clay minerals is apparently able to reduce the ecotoxicity. In ferralsol mixtures, lower dosages of sediment application (3.33 and 6.66%) caused significant effects on microcrustaceans and algae. In chernosol treatments, adverse effects on in micro-crustaceans and algae were only observed for the doses of 6.58 and 13.16%, respectively. Such data indicate occurrence of potential risks on aquatic biota in the scenario where sediment-amended soils could be leached and such solutions could contaminate surrounding fluvial systems. The bioassay with E. andrei using contact paper also suggests the occurrence of potential adverse effects on edaphic biota. In addition, such tests with E. andrei demonstrate that they are highly applicable as alternative tools to monitor potential ecotoxicity associated with terrestrial disposal of solid residues containing domestic wastes and/or contaminated with metals.