Concentrations of Pb, Cd and Zn in sediments of an estuarine complex affected by ancient mining activities in Southeast Brazil

Abstract

An artificial canal, built in 1852, diverted 60% of the flow of the Ribeira de Iguape River (RIR) into the northern region of the Estuarine-Lagoon Complex of Iguape-Cananéia (ELCIC), Southeast Brazil. Since then the river has become the main contributor of fresh water and suspended matter into the system. Additionally, the RIR was contaminated by mining activities, especially of Pb, which disposed their wastes directly into this river from their beginning until its cease in 1996. Thus, unknown quantities of metals began to be continuously introduced into the ELCIC. This study evaluated lead, cadmium and zinc concentrations in the surficial sediment at 10 points sampled along the ELCIC, 15 years after the closure of the mining. Zinc concentrations were in accordance with legislation and similar across the ELCIC regions, ranging from 10.4 to 22.8 µg.g-1. Lead concentrations ranged from 19.3 to 67.9 µg.g-1, with higher concentrations in the northern ELCIC region, especially in areas near to the canal and the mouth of the RIR. These values were above the Level I limits established by the Brazilian Environmental Agency, suggesting the possibility of a sediment toxicity. Cadmium was only detected (up to 3.6 µg.g-1) in the northern region, exceeding Level I limits too. However, Pb and Cd values were not above the Level II limits. Results revealed areas of moderate lead and cadmium contamination in the northern ELCIC region, still indicating a strong contribution from the ancient mining activities and from other current anthropogenic activities such as agriculture or an incorrect disposal of sewage and residues. Therefore, a continuous assessment of metal concentrations in the sedimentary record is important to monitor the ELCIC environmental quality.