贵州赫章土法炼锌导致的重金属积累

ZINC SMELTING-AN IMPORTANT FACTOR LEADING TO HEAVY METAL ACCUMULATION IN SOILS AND SEDIMENTS IN HEZHANG COUNTY, GUIZHOU PROVINCE

贵州省赫章县的土法炼锌不仅导致植被的破坏,而且使附近土壤和溪流沉积物中重金属有不同程度的积累,土壤中w(Pb)达到37.24×10^(-6)～30100×10^(6),w(Zn)为162.23×10^(-6)～31625×10^(-6),w(Cd)为0.50×10^(-6)～113×10^(-6),大大超过了当地的土壤背景值;沉积物中w(Pb)达到325.00×10^(-6)～21850×10^(-6),w(Zn)为1250.00×10^(-6)～30425×10^(-6),w(Cd)为25×10^(-6)～97×10^(-6)。土壤和沉积物中Pb、Zn含量与Fe_2O_3有极显著的正相关性;土壤中重金属Pb、Zn含量与Al_2O_3有极显著的正相关性,而沉积物中Pb、Zn含量与Al_2O_3则没有相关性。土壤和沉积物中铁矿物(铁氧化物和氢氧化物)对重金属的强烈固定作用。连续提取法对化学形态研究表明,Pb、Zn在土壤中主要表现为铁锰氧化物结合态与残渣态,而在沉积物中则主要为碳酸盐结合态、残渣态和铁锰氧化物结合态。土壤中可交换态Pb、Zn所占的比例很小,但其绝对含量变化较大,w(Pb)从最低2.75×10^(-6)到最高310.41×10^(-6),w(Zn)4.94×10^(-6)～321.10×10^(-6)。沉积物中w(Pb)7.42×10^(-6)～98.91×10^(-6);w(Zn)9.97×10^(-6)～72.67×10^(-6)。土壤中重金属Pb、Zn的有效性程度明显高于溪流沉积物,对生态环境的潜在危害更大。

Local zinc smelting with indigenous method in Hezhang County, Guizhou Province, not only caused infertile vegetation, but also induced varying-degree accumulation of heavy metals in adjacent soils and stream sediments. The heavy metal Pb in soils varies from37.24 ×10-6 to 30100× 10-6,Zn from 162.23 × 10-6 to 31625 × 10-6,while Cd from 0.50 × 10-6 to 113 × 10-6, which obviously exceed the background values of local soils, while the heavy metal Pb in stream sediments varies from325.00× 10-6 to 21850 × 10-6,Zn from 1250.00 × 10-6 to 30425 ×10-6,and Cd from25 × 10-6 to 97 × 10-6. And extremely obvious positive correlations can be observed between the heavy metal Pb and Zn contents in soils and sediments and their Fe2O3 levels; these correlations can also be observed in soils between Pb and Zn contents and soil Al2O3 levels, but no in stream sediments. This implies that iron minerals in soils and sediments (such as iron oxide and iron hydroxide) are strongly capable of fixing heavy metals. Sequential extraction results indicated the overwhelming chemical forms of Pb and Zn were Fe, Mn oxide bound and residual forms in soils, while carbonate bound, residue and Fe, Mn oxide bound forms in stream sediments. Exchangeable fraction of Pb, Zn in soils only has a very low percentage but their absolute concentrations are highly variable. Exchangeable Pb fraction varies from 2.75 × 10-6 to 310.41 × 10-6 in concentration, while Zn from 4. 94 × 10-6 to 321. 10 × 10-6 in concentration. In sediments, exchangeable Pb varies from 7. 42× 10-6 to 98. 91 × 10-6; while Zn from 9. 97 × 10-6 to 72. 67 × 10-6. The bioavailability of Pb and Zn in soils is obviously higher than in sediments, indicating a more potential toxicity to the eco-environment.