Contaminação por elementos terras raras em áreas de mineração de ouro na Amazônia oriental

Abstract

Gold (Au) is exploited by rudimentary methods in several artisanal mines in the Amazon, which generates residues that can harm the ecosystem and public health with pollution by rare earth elements (REEs). The objectives of this study were to determine the concentrations and risks of REEs in areas altered by artisanal Au mining in the southeastern and northeastern Amazon. The areas studied in the southeastern Amazon referred to the zone of influence of the artisanal mine of Serra Pelada, located in the municipality of Curionópolis, state of Pará, and included agricultural, urban, mining, and native forest areas. In the northeastern Amazon, the areas studied corresponded to artisanal Au mines in Cachoeira do Piriá, state of Pará, where miners use methods such as underground exploration, reprocessing by cyanidation, and surface colluvial mining. Samples were collected and submitted to chemical and granulometric characterization. The concentrations of REEs were quantified by inductively coupled plasma mass spectrometry and used to estimate levels of pollution and risks to the environment and human health. In general, the properties showed marked differences between areas without significant anthropic impact and altered areas, which had lower levels of organic matter and less acidity. Most REEs had higher concentrations in anthropized areas when compared to reference areas. The most alarming contamination factors were observed for lanthanum (La) and yttrium (Y) in agricultural areas in Serra Pelada, and for cerium (Ce), europium (Eu), La, neodymium (Nd), praseodymium (Pr), samarium (Sm), and scandium (Sc) in the underground and cyanidation mining areas in Cachoeira do Piriá. The highest enrichment factors were observed for Y in Serra Pelada, ranging from 18.2 to 44.4, and for Ce, La, Nd, Pr, and Sc in Cachoeira do Piriá, ranging from 5.5 to 20. The ecological risks from individual exposure to REEs were low in all areas studied, but simultaneous exposure was associated with risks ranging from moderate (167.3) to high (365.7) in Cachoeira do Piriá. On the other hand, risks to the health of adults and children were not evidenced. The results of this study indicate that mitigation measures must be implemented to protect the environment from the impacts of REEs, considering the levels of pollution, enrichment, and ecological risks of these emerging pollutants in areas altered by human activities in the eastern Amazon.