Terrestrial disposal of coal mining residues: acid drainage, acute ecotoxicity and bioavailability of heavy metals

Abstract

Terrestrial disposal of coal mining residues: acid drainage, acute ecotoxicity and bioavailability of heavy metals -Potential bioavailability and acute ecotoxicity associated with terrestrial disposal of coal mining residues were studied through acute bioassays with earthworms (Eisenia andrei), lettuce (Lactuca sativa) and aquatic micro-crustaceans (Daphnia similis). A composed sample of coal mining residue was collected at some surface deposits at the Urussanga river Basin, one of the three basis of the Southern Santa Catarina Coal Basin, an area highly degraded by mining activities. The bioassays were performed according to procedures described in standard protocols (ASTM, ISO and ABNT). In a hypothetic risk scenario of pyrite acute exposure, the results indicated low levels of ecotoxicity and low bioavailability of toxic metals for earthworms. Significant effects on the germination and morphology of L. sativa were only detected for high rates (~50%) of residue application on the soil. It is probable that such low toxicity levels are related to the short time of pyrite exposure to oxygen, generating a less intense acid drainage. For D. similis, significant damages (immobility) were observed for doses higher than 25% in elutriates, suggesting the occurrence of adverse effects in scenarios where such coal mining residues could be leached.