Ecological and human health risk assessment of sediments from the São Domingos old mining área

The legacy of abandoned mining sites poses a major threat to both the environment and human health due to the possible accumulation of potentially toxic elements in soils and sediments. The São Domingos mining area, located in the Iberian Pyrite Belt, represents one such site, where mining activities ceased without the implementation of environmental control or remediation measures. As a consequence, high concentrations of potentially toxic elements have accumulated throughout the surrounding area, leading to severe environmental degradation.

In this context, to improve the understanding of ecological and human health risks in this area, sediment samples were collected from four drills carried out at spaced locations along approximately 5 km of the former mining area. The samples were separated into two grain-size fractions (<2 mm and <2 µm), the latter being particularly relevant due to its enhanced capacity to retain contaminants. Geochemical analyses were performed, and contamination levels were evaluated using several ecological risk indices, including the contamination factor, the geoaccumulation index, and the potential ecological risk index. Human health risks were assessed using the hazard quotient and cancer risk approaches, considering multiple exposure pathways, namely ingestion, inhalation, and dermal contact, for both adults and children.

The results show that potentially toxic element concentrations in most drills largely exceed background values, particularly in the <2 µm fraction. Very high ecological risk levels were identified, well above established thresholds, and the geoaccumulation index classifies several elements as extremely polluted. Human health risk assessment reveals significant non-carcinogenic and carcinogenic risks, with children identified as the most vulnerable population group. Hg, Pb, and As were the elements that contributed most significantly to the observed ecological and human health risks. The most hazardous drills are located close to former ore extraction and processing areas, with a progressive decrease in both environmental and human health risks observed with increasing distance from these zones. These findings are particularly important due to frequent tourist visits throughout the year and the presence of nearby communities, highlighting the potential for widespread human exposure.

Overall, this study demonstrates that the São Domingos mining area represents a serious ecological and public health concern, highlighting the urgent need for remediation measures and continuous environmental monitoring.