Study On Heavy Metal Speciation In Sediments Of Ya'er Lake

The mobilization capacity and environmental toxicity of heavy metals in the surface sediments are not only related to their total content, but also depends on their speciation. In order to clarify the pollution status of heavy metals in Ya'er Lake which located in Ezhou in Hubei Province, we collected materials about Ya're Lake and took eleven samples, the we extracted the specifies of Pb, Cu, Zn, Cr, Cd, Ni through the Modified BCR protocol published by Rauret. et al. Then the extracted liquids were treated and determinate the concentration of heavy metals by Flame atomic absorption spectrometric method (FAAS). Through experiments and analysis, this paper has the following conclusions:(1)The approximate concentration of six elements is stated below: Pb: 46.35~116.24mg/kg; Cu:132.36~1836.57mg/kg; Cr:35.00~73.87mg/kg; Zn:169.30~316.68mg/kg; Cd:4.31~9.78mg/kg; Ni:18.11~76.21mg/kg.(2)The total concentration of six elements decline with the flow direction, but the total content and non-stable fractions of Pb, Cu, Zn, Cr, Cd increase in No.4 oxidation pond in center of the lake.(3)The amount of the six elements in the first three oxidation ponds in the inlet of lake showed a significantly increase - slow growth trend, while the dominant speciation of them changed from exchangeable and acid soluble fraction, reducible fraction to oxidizable and residual fraction.(4) Residue fraction of Pb, Cr and Ni is the dominant in the proportion of speciation distribution (approximately 75%). Copper mainly exists in the surface sediments of Ya'er Lake in residual and oxidizable fractions. The latter one takes about 20%~40% in the distribution. These parts of the heavy metals can be re-released into water under oxidation conditions. Therefore, it has potential biological availability and toxicity. That means these three metals are relatively stable. They can't easily return into water phase from the flow with pollutants and sediment. (5) Non-steady fractions of Zn and Cd take about 50%~60% in their proportion of speciation distributions. Especially, the exchangeable and acid soluble fraction takes 20%~40% in the distributions. This part of the heavy metals, which can be released from the sediments under certain conditions, has a high transport capacity and a high ability of secondary release.