土法炼锌导致Cd对土壤-农作物系统污染的研究

Cadmium Contamination in the Soil-crop System Induced by Local Zinc Smelting Activities in Hezhang County,Guizhou Province

采用现场取样及室内分析方法,研究了贵州省赫章县的土法炼锌活动导致Cd对当地土壤-农作物系统的污染状况及规律。结果表明,炼锌污染土壤Cd含量高达5.3～144.7mg·kg-1,且Cd在土壤中的累积程度随着冶炼时间的增长而加剧。形态分析结果显示,土壤中的CaCl2和DTPA提取态Cd分别占全量的2.47%～16.80%和3.18%～10.11%,随着Cd在土壤中累积时间的加长,CaCl2和DTPA提取态Cd的百分含量均呈显著下降趋势。土壤污染导致农作物体内Cd的明显蓄积,玉米、土豆和大豆三类当地主要农作物可食部分Cd含量分别为1.8、4.8和2.0mg·kg-1,分别超过国家粮食卫生标准9、24和10倍。相关分析结果显示,CaCl2提取态Cd与农作物中Cd含量没有相关关系,而DTPA提取态Cd和全量Cd与农作物根和茎叶中Cd含量显著正相关。

The soil-crop system was seriously contaminated by cadmium due to local zinc smelting activities with indigenous methods in Hezhang County, Guizhou Province. Cadmium concentrations in vicinity soils were as high as 5.3-144.7 mg·kg^-1, and were increasing with the lengthening of the smelting history. Generally, contamination level of Cd decreased with distance from the smelting area though this trend differed somewhat in different smelting areas. The vertical distribution of Cd in soil profile showed that Cd was mainly enriched in the top soil （0-5 cm）, however, the deep layer soil （50-60 cm） was also contaminated by Cd to some extent. Chemical fractions of Cd were extracted by 0.01 mol ·L^-1 CaCl2 and 0.005 mol·L^-1 DTPA, the results showed that the CaCl2 extractable and DTPA extractable fraction accounted for 2.47%-16.80 % and 3.18%- 10.11% of the total content, respectively. In addition, these percentages would decrease notably with increasing residence time of cadmium in soil. Cadmium contamination in soil resulted in high level Cd content in crop tissues. Cadmium content in edible parts of maize, potato and soybean averaged 1.8 mg·kg^-1, 4.8 mg·kg^-1 and 2.0 mg·kg^-1, respectively, which were 9, 24 and 10 times higher than the maximum permit limit in China. Correlation analyses demonstrated that soil CaCl2 extractable Cd was not correlated with Cd concentrations in crops, whereas the DTPA extractable fraction and total Cd concentration were correlated significantly with the Cd concentration in roots, stems and leaves of crops.