RESUMO
Field work was conducted in the Yangtze (Changjiang River) estuary in April, 2006. Water and surface sediment samples were collected to analyze total arsenic and different arsenic species, and to assess the bioavailability. Water samples were filtered through 0.45 microm filter membrane to determine the concentrations of dissolved arsenic, while the unfiltered water samples were digested by acid to determine the concentrations of total arsenic, and the difference between them was the concentrations of particulate arsenic. It is showed that the concentrations of total arsenic varied from 0.88 microg x L(-1) to 1.35 microg x L(-) at the slack of flood tide, and from 2.37 microg x L(-1) to 3.35 microg x L(-1) at the slack of ebb tide in water column of the Qingcaosha waters in the Yangtze estuary. The concentrations of both dissolved and particulate arsenic varied with the tide time. The concentrations of arsenic species at the slack of ebb tide were higher than those at the slack of flood tide, so did the percentage of particulate arsenic accounting for total arsenic. Phosphoric acid of 0.3 mol x L(-1) can effectively extract arsenate, arsenite, monomethylarsenate (MMA) and dimethylarsenite (DMA) from the sediments with the aid of microwave. The arsenic species in the extracts were detected by the hyphenated method of High Performance Liquid Chromatography-Hydrogenation-Atom Absorption Spectrometry (HPLC-HGAAS). The concentrations of total arsenic in surface sediments varied between 6.3 mg x kg(-1) and 30.7 mg x kg(-1), which were mainly contributed by inorganic arsenic species. Arsenate was dominated in the sediments in the offshore waters while arsenite was dominated in the sediments in longshore waters. The concentrations of available arsenic in the sediments, which were estimated by the method of acetate cellulose composite membrane embedded with iron oxides (FeO/CAM), accounted for 0.6% to 3.9% (averaged as 2.1%) of the total arsenic concentrations. The available arsenic concentrations had no significant correlation with the total arsenic concentrations, but had significant positive correlation with the arsenate concentrations and had significant negative correlation with the arsenite concentrations. The results also showed that the distribution of arsenic species in the sediments and their bioavailability in the South Branch of the Yangtze estuary were significantly influenced by the tributary river flows and effluents from the urban area.
