Speciation And Bioavailability Of Arsenic In Aquatic Sediments

In recent years, more and more attention was paid to the effect of arsenic on the human health and aqueous organisms. It is clearly established that the toxicity and bioavailability were depend on arsenic speciation. Therefore, it was necessary to analyse and evaluate the speciation and bioavailabity of arsenic. A case study on the speciation and bioavilability of arsenic in the aqueous sediments was carried out in the estuary of the Yangtze River(Changjiang).An on-line coupling system of high performance liquid chromatography -hydride generation- atomic absorption spectrometry(HPLC-HG-AAS) for arsenic speciation analysis had been optimized. The method for As(III), As(V), DMA and MMA's analysis was sensitive, precise, stable and reliable (the variation coefficient was less than 10%). A microwave-assisted extraction method using 0.3 mol/L moorthophosphoric acid as extract had been proposed for arsenic speciation analysis in the sediment and the recovery rate was in the area of 90.8%～103.5%.A new method was developed to assess the bioavailability of arsenic in the sediments by using an iron oxide/cellulose acetate membrane (FeO/CAM).The results show that in water, the amount of bioavailable arsenic by FeO/CAM desorbed from the sediment decreased exponentially with the ratio of sediment to water and then went planar and bioavailable arsenic desorption would come to equilibrium after 24h, this process mimicked biological absorption, so FeO/CAM could be used to measure available arsenic. The amount of bioavailable arsenic in twelve sediment samples from Taihu lake, which total concentrations of arsenic ranged from 6.4～34.6 mg/kg was estimated by FeO/CAM method. The results show that the concentrations of bioavailable arsenic estimated by FeO/CAM were significantly correlated with those estimated by phosphate buffer. Compared with the chemical extraction, the FeO/CAM method overcomes an ultimate limitation that some non-bioavailable arsenic could be extracted. Therefore, the FeO/CAM method is a closer estimate of bioavailable arsenic.Water and surface sediments were collected in April 2006, and the contents of total arsenic, different arsenic species and bioavailable arsenic had been analysed. The results showed that the content of total arsenic in the sediments of Yangtze River was ranging from 9.56 mg/kg to 21.58 mg/kg; As(V) was the major speciation in sediment; the concentration of bioavailable arsenic was low (0.06～0.69 mg/kg), especially the sediments was away from the wastewater drain outlets; the index of Müller's geoaccumulation index method and Hakanson's ecological risk index method showed the sediments of Yangtze River was micro-polluted.