土法炼锌区生态退化与重金属污染

Ecological degeneration and heavy metals pollution in zinc smelting areas

土法炼锌致使冶炼区大量重金属的累积以及生态环境的严重破坏。研究以土法炼锌的集中点妈姑为例,探索了土法炼锌区的土壤和植被退化现状,以及重金属的分布规律,为废弃地的生态重建与污染修复提供科学依据。冶炼造成大面积的植被破坏,成为裸地,停止冶炼后,植被自然恢复极为缓慢,特别是废渣堆放处。冶炼残渣具有较高的pH值和EC值、低CEC,有机质极为缺乏,含N量低。冶炼区污染土壤明显酸化,导致P有效性降低。冶炼废渣具有高的孔隙度和良好的通气性,但持水保水能力差。冶炼废渣的Pb、Zn、Cd含量分别为4632mg/kg、8968mg/kg、58mg/kg。污染土壤的Pb、Zn、Cd含量分别为234mg/kg、400mg/kg、9.6mg/kg。污染土壤中Pb、Zn、Cd的DTPA提取态百分比分别为6.8%、19.97%、29.72%。废渣中Pb、Zn、Cd的DTPA提取态百分比分别为0.44%、1.36%、4.80%,但其绝对含量接近于污染土壤,具有较大环境风险性。

Indigenous zinc smelting activity, widely spread in western Guizhou, China, had caused serious pollution of heavy metals and ecological destruction in the indigenous zinc smelting areas. Soil and vegetation degeneration and distribution of heavy metals were investigated in Magu town in order to provide scientific base for the approach to revegetation and pollution remediation. The indigenous zinc smelting activities destroyed vegetation around the smelting areas. The natural restoration for vegetation was quite slow on smelting waste land, especially on smelting residues. Smelting residues had higher pH values and EC values, lower CEC values, and lower organic matter and nitrogen than background soils. The pH values and bioavailable P contents in contaminated soils decreased compared to background soils. The smelting residues still had high porosity and aeration, however, their abilities to maintain soil moisture and fertility were very poor. Concentrations of Pb, Zn and Cd in smelting residues averaged at 4 632 mg/kg, 8 968 mg/kg, and 58 mg/kg, respectively, whereas 234 mg/kg Pb, 400 mg/kg Zn and 9.6 mg/kg Cd occurred in soil around the smelting areas. DTPA-available Pb, Zn and Cd accounted for 6.8%, 19.97% and 29.72% of the total content in contaminated soils, respectively. DTPA-available Pb, Zn and Cd accounted for 0.44%, 1.36% and 4.80% of the total content in smelting residues, respectively, while the absolute concentrations were quite high, indicating a potential toxicity to eco-environment.