The pollution of aquatic ecosystems by heavy metals has assumed serious proportions due to their toxicity and accumulative behavior. River dams are especially at risk of contamination by different contaminants from anthropogenic sources including heavy metals since change of the sediment regime often occurs. The largest hydropower dam and reservoir system along the entire Danube, the Iron Gate, is located at the Djerdap Gorge (117 km long) in Serbia and Montenegro. In order to determine the degree of pollution of the Iron Gate by heavy metals, composite sediment samples were collected from seven reaches of the river from Smederevo (river-km 1112) upstream from the Iron Gate dam to Radujevac (river-km 851) downstream from the gorge. The concentrations of As, Cd, Cr, Cu, Fe, Pb, Mn, Hg, Ni and Zn were determined in the sediments. The lowest heavy metal concentrations were measured around river-km 854, downstream from the gorge. The data from this study were compared with data obtained 20 years ago in the same area. It was found that the range of mean concentrations over the entire gorge of Fe, Mn, Ni, Zn, Cu, Cr and Cd increased by 46.6% (Zn at the site Tekija) to 156.2% (Ni at the site Veliko Gradiste). Decreases in concentrations were observed for Hg and Pb. Metal levels in the sediments did not exceed Dutch intervention values, but were higher than the target values for Ni, Zn, Cu, Cr and especially for Cd, indicating contamination not sufficiently high to require remediation/intervention, but not excluding risk to the ecosystem.
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