武汉东湖沉积物中重金属生物有效性研究

The Studies on the Bioavailability of Heavy Metals in the Sediments of Lake Donghu, Wuhan

沉积物中的酸挥发性硫化物(AVS)是预测厌氧沉积物中重金属生物有效性的重要参数,SEM/AVS大于1时沉积物中重金属具有潜在生物毒性,小于1时则无生物有效性. 本文研究了东湖三个不同污染负荷的站点的同步提取金属SEM(Cu, Zn, Pb, Cd, Ni, Co, Ag, Cr)和SEM/AVS的深度分布,研究表明东湖沉积物中主要重金属是Zn, Cr和Cu,约占SEM总量的90%. I站、II站沉积物中AVS是重金属生物有效性的主控因子之一,对重金属的深度分布影响较大,重金属不具有生物有效性;III站沉积物中AVS对重金属的深度分布影响较小,重金属具有潜在的生物毒性. 相关分析表明,I站、II站沉积物中Cr、Ni、Ag、Cd与AVS在P<0.05有显著性相关,AVS对这些金属的深度分布具有更强的控制作用;虽然两站沉积物中Cr的含量差别不大,东湖I站沉积物中Cr/AVS比值(0.02)显著高于II站(0.003),沉积物中Cr与硫化物的结合主要是受还原反应的影响.

Acid-volatile sulfides (AVS), which can form insoluble sulfides complexes with minimal biological availability with a number of cationic metals, is a key partitioning phase controlling metal bioavailability in the sediments. Toxic effects were found to be absent for SEM/AVS ratios smaller than one, but appeared to be present at SEM/AVS ratios exceeding one. This study investigated the vertical distribution of SEM (Cu, Zn, Pb, Cd, Ni, Co, Ag, Cr) and SEM/AVS ratio in the sediments cores of three different polluted stations in Lake Donghu, Wuhan. It was found that the metal concentrations were in the order of Zn>Cr>Cu>Ni≈Pb>>Ag≈Cd. Among heavy metals, Zn, Cr and Cu were the dominating species, accounting for nearly 90% of SEM. At Station I and II, AVS was the key factor to control the bioavailability of metals, and SEM/AVS ratios were less than one. Significant linear relationship between AVS and metals at Station I and II confirmed that AVS had a great effect on the vertical distribution of metals. However, at Station III, SEM/AVS ratios were larger than one, and no significant linear relationship between AVS and metals was found. The sediments in Station III have potential metal toxicity. Significant linear relationships were observed between trace metals (Cr, Ni, Ag, Cd) and AVS at Station I and II, indicating that these metals were associated to the AVS phase in the sediments more than other metals. Especially there was a close relationship between SEM-Ag and AVS in the sediments at both stations (r = 0.6973, Station I;r = 0.7786, Station II). Our results also show that there was a higher SEM-Cr/AVS ratio in the sediment with high AVS (Station I, r = 0.7129) than in the sediment with low AVS (Station II, r = 0.4114) while SEM-Cr level did not differ significantly in both stations. It seems likely that Cr is strongly influenced by complex redox reaction pathways rather than simple substitution reactions, and tends to be absorbed on , or coprecipitate with iron sulfide phases in an anoxic environment more than a slight anoxic environment.