Release and kinetics of arsenic and plumbum in the Songhua River surficial sediments.

To estimate the pollution of As and Pb in the Songhua River which flows through the major rice-producing regions in China, the present study investigated the level and release of As and Pb in surficial sediments which collected from nine sites in Songhua River (M1-M9). The concentration of As and Pb was ranged as follows: As = 3.104~15.01 μg/g, Pb = 20.10~37.42 μg/g; the average concentration: As = 6.466 ± 3.077 μg/g, Pb = 28.88 ± 5.077 μg/g. By analysis vertically, the average concentration of As was 5.166 ± 1.496 μg/g in the upstream, 5.815 ± 1.793 μg/g in the midstream, and 9.716 ± 4.977 μg/g in the downstream. The average concentration of Pb was 27.83 ± 4.552 μg/g in the upstream, 28.66 ± 6.333 μg/g in the midstream, and 30.99 ± 4.837 μg/g in the downstream. It indicated that the concentration of As and Pb increased gradually from upstream to downstream. As existed mainly as insoluble state and Pb existed mainly as sulfide and organic combining state in surficial sediments, and the species of As and Pb could transform with the change of the circumstance. The release of quantity of As was higher than Pb. The pH of 6 was not conducive to the release of As and Pb. When the temperature was 35 and 6 °C, the release of As and Pb in surficial sediments were restrained, respectively. Fumaric acid and citric acid played an important role in promoting the release of As, but not conducive to Pb. Furthermore, the reasonable aeration rate was beneficial to the release process of As and Pb in surficial sediment. By kinetic analysis, the Elovich equation (Ct = 84.931-8.952lnt) could be used to describe the dynamic process of the release of As in a relatively short time. The Elovich equation (C t  = 2.724 + 1.3724lnt) and double constant rate equation (lnC T  = 1.4646 + 0.1522lnT) could well describe the dynamics process of the release of Pb.