Geochemical characteristics of bottom sediments in the Odra River estuary - Roztoka Odrzańska (north-west Poland)

Roztoka Odrzańska is the last section of the Odra River estuary. Both in 1996, and in 1999 concentrations of Zn, Cu, Pb, Cd and Hg in the surface waters of Roztoka Odrzańska were within the limits for I class of purity. Maps of the heavy metal distributions in bottom sediments resemble those of TOC distribution in the < 0.20 mm fraction. Overall, 58.3% of the bottom sediments of Roztoka Odrzańska in 1996, as regards concentrations of Cd, Zn, Pb, Cu and Hg, belonged to class IV of purity; 14.6% belonged to class III; 18.8% belonged to class II and 8.3% to class I at all research stations. The excessive pollution the Roztoka Odrzańska sediments is controlled mainly by Cd and Zn concentrations and, to a much lower degree by Pb. Analyses in 1999 showed similar average concentrations of Cu, Zn and Pb, but less than half the content of cadmium. Concentrations, though, of cobalt (1.8x) and especially mercury (22.7x) were higher than the 1996 average levels. The observed concentrations fall within the concentration limits recorded in 1996 for Cu, Zn, Pb, Cd and Co, but they exceed these limits considerably for Hg.