Metal speciation in sediments from Rosia Motana mining area, Romania

Abstract

The objective of the study was to investigate the distribution of the metallic elements Cu, Cr, Ni, Pb and Zn in water column (surface and pore water) and also in the sediment structure („total” concentration dissolved by aqua regia and speciation using BCR sequential extraction procedure on wet sediment) from eight artificial lakes situated around a gold and silver mining area from Rosia Montana, Romania. The sedimentary metal content was fractionated into four fractions: carbonate and exchangeable, metals bound to Fe and Mn oxides, metals bound to organic matter and finally, residual fraction. The extracts were analyzed using flame atomic absorption spectrometry. Cr and Pb metallic species were not founded in exchangeable forms inside the sediment bodies and are not available for the aquatic ecosystem. Based on average values for the studied sites, the highest bioavailable content in sediments was reported in Taul Mare Lake (Cu, 23%), in Taul Cartus Lake (Cu, 23%; Zn, 48%) and in Taul Tapului Lake (Ni, 58%). The major problems are also associated with rich content of total metals in above mentioned Lakes. The highest pollution risk is present in Taul Tapului Lake, situated near a waste sterile mining dump. Different factors, such as: decrease of the pH, accidental release of oxidizing and reducing agents, can disturb the natural equilibrium of the aquatic ecosystem and can release metallic compounds bounded not only in exchangeable form (Cu, Ni, Zn), but also bounded by organic matter, Fe and Mn oxides (Cr, Pb).