[Transfer and release of Hg from the Yangtze Estuarine sediment during sediment resuspension event].

ABSTRACT

The effect of resuspension energy and duration on release and subsequent redistribution of sediment bound Hg in Yangtze Estuary was measured experimentally using a particle entrainment simulator. Concentrations of Hg(D) (Dissolved Hg) and Hg(P) (Particulate Hg) in the overlying water were 34-268 ng x L(-1) and 25-195 microg x kg(-1) respectively, and sensitive to disturbance energy and time during sediment resuspension. There is no significant correlation between Hg(D) and Hg(P) concentration. After the first disturbance intensity experiment for 3 h, Hg was released to the overlying water in general, with Hg(D) and Hg(P) concentrations increasing from 179 ng x L(-1) to 268 ng x L(-1) and from 116 microg x kg(-1) to 139 microg x kg(-1) respectively. And then concentrations of Hg(D) and Hg(P) decreased after the overlying water was disturbed for 3 h at the second intensity, while after the third disturbance intensity experiment for 3 h, a slight increase was observed in Hg(D), and Hg(P) concentration increased from 89 microg x kg(-1) to 162 microg x kg(-1) in overlying water. The distribution coefficient (lg K(d)) of Hg in overlying water had no significant correlations with the water column pH, Eh, DO and TSS, but influenced by the combined physical and chemical conditions of the water column. In each disturbance energy treatment, both the content of suspended particles and lg K(d) for Hg increased rapidly in the overlying water in the early stage, especially the first 5 min, indicating a strong absorption of Hg on the suspended particles. After that, a decrease of the lg K(d) for Hg occurred with the time and content of suspended particles increased. It can be explained that the released Hg by oxidation of sulfide was bounded by the newly generated colloidal material such as the hydrate iron-manganese oxide. In relatively strong disturbance energy treatment, part of the coarse particles settled with time. The concentrations of Hg(P) increased in some resuspension stage in the overlying water due to the "fine particle concentration effect".