Influência da Salinidade na Toxicidade de Sedimentos Dragados da Lagoa Rodrigo de Freitas e Baía de Guanabara (RJ): Efeitos Tóxicos em Minhocas

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The role of salinity levels in the toxicity of dredged sediments from estuarine systems, in scenario of land disposal, was investigated by using Eisenia andrei as bioindicator. Samples of ferralsol and chernosol were collected and salinized with seawater (2 and 12 g/kg of salt) and submitted to acute and avoidance bioassays with E. andrei. Data of salinity and sediment LC 50 were extracted from the literature. These data consists of results from acute bioassays with E. andrei applied to dredged sediments from Rodrigo de Freitas Lagoon and Guanabara Bay. The concentration of salt (g/kg) in soil:sediment mixture that corresponded to the LC 50 was estimated by determining salt contents in pure soils and sediments. When such concentration is close to the LC 50 obtained in laboratory using seawater, the influence of the salt in the toxicity was considered preponderant. The results revealed that concentrations of salt ≥ 3g/kg are significantly lethal to the organisms in both soil types, but toxicity levels are higher in ferralsol (LC 50 = 3,51 g/kg) than those observed in chernosol (LC 50 = 4,03 g/kg). Concentrations of salt ≥ 2g/kg were able to cause significant avoidance responses, but again the value of EC 50 in ferralsol (2,77 g/kg) were lower than that obtained in chernosol (2,99 g/kg). These observations are due to the abundance of expansive clay minerals in chernosol, with high cationic exchange capacity and that are able to reduce toxicity levels. The sediments whose salt concentrations in the sediment LC 50 (soil:sediment mixture) are close to the salt LC 50 values determined in laboratory are the APA of Guapimirim (winter), Porto of Rio (winter), Port of Niteroi (summer), Rodrigo de Freitas Lagoon (in chernosol) and the mouth of Meriti River (winter), suggesting that the concentrations of salts are sufficiently high to play a crucial role in the toxicity. Regarding the other study areas, other factors, such as the properties of the sediments, heavy metals and organic substances, may play an important role in the toxicity.