Avaliação ecotoxicológica de impactos da contaminação por metais e arsênio em áreas de mineração e beneficiamento de ouro em Minas Gerais

Abstract

Mining is one of the most important activities for economic profits although among the ones causing more environmental impacts. The effects either in extraction areas or in processing and production areas cause several contaminants release, mainly metals, polluting water, sediment and soil, reducing environment quality and resulting in risk for human health. Gold is the most valued and profitable precious metal and its extraction cause the most severe environmental impacts, showing a strong correlation with acid drainage and arsenic release. Arsenic presents different valences in the environment and is very toxic to biota. This study is part of a series of researches developed in areas influenced by extractions and processing gold mining activities funded by Science and Technology National Institute (INCT-ACQUA). It aimed to evaluate ecotoxicological approaches in water and sediment of these areas. In addition, where arsenic release had correlation with a gold mine, we tried to evaluate the arsenic toxicity potential alone and associated with iron, a common metal in areas of the present studies, used for coagulation of severe metals in remediation actions. Toxicity bioassays and tests were conducted with Daphnia similis, Ceriodaphnia silvestrii and Chironomus xanthus according to specific standards. For evaluation of the processing and extraction gold mining areas, physical and chemical parameters including pH, dissolved oxygen, electric conductivity, dissolved solids, hardness, alkalinity and metals were determined. The results showed CE50 e CI25 for cladocerans, higher than legislation values. However, CE50 was reduced to half when arsenic was associated with iron at 0,02 mg.L-1. The study areas influenced by gold processing activity (Mina Stream and Mutuca Stream) and by gold extraction activity (P1, P2 e P3), showed high metals and arsenic contamination in water and sediment. These results were corroborated by the toxicity bioassays. Thus, the consistency between ecotoxicological tools and chemical data emphasized the importance of the ecotoxicological approach. Although in the second area, the mining activity had been deactivated for five years, toxicity effects in sediment and soil were higher than in the first area. Considering the proximity of both sites to local populations and streams, ecological risk assessment and mitigation actions are fundamental to ensure environmental and human health in those areas.