风险评价代码法对农田土壤重金属生态风险的评价

Ecological risk of heavy metals in agricultral soils assessed by risk assessment code

为揭示矿区周边农田土壤中重金属分布特征及其潜在生态风险,于2013年在云南省某铅锌矿周边的农田土壤共布设68个采样点,分析土壤中Cd、Hg、As、Pb、Cr、Cu和Zn的含量及污染程度,并采用改进的BCR法测定了各重金属形态分布特征,在此基础上运用风险评价代码法评价了重金属的潜在风险程度.结果表明,7种重金属都存在不同程度的超标,其中超标最严重的是Cd和Zn,超标率分别达到92.6%和75%.7种重金属化学形态也不尽相同:在重金属有效态中,Cd的水溶态和可提取态较高(平均值达到31.2%);Pb、Cu和Zn可还原态、可氧化态这两部分含量较高,两部分之和的平均值分别可达到27.9%、30%和29.2%;Hg、As和Cr的残渣态含量较高,平均值分别为90.4%、72.9%和76.8%.风险评价代码评价结果表明,54.4%的样点Cd为高生态风险,45.6%的样点Cd为中度生态风险;100%的样点Zn为中度生态风险;Cu有41.2%的点位属于低生态风险,58.8%的点位属于中度生态风险;As和Pb主要以低生态风险为主(所占比例分别为92.6%和91.8%);Hg主要以无生态风险为主(所占97.1%).综上,该矿区周边农田土壤受到了严重的重金属污染,其中土壤中Cd的生态风险最高,同时,Zn和Cu的生态风险也不容忽视.

In order to investigate the distribution characteristics of heavy metals in agricultural soil around Pb-Zn mine area,soil samples at 68 sites were collected in 2013 in Yunnan Province,China. Contents of heavy metals（ Cd,Hg,As,Pb,Cr,Cu and Zn） were measured. The modified BCR sequential extraction method was applied to evaluate the chemical speciation of these heavy metals. The potential ecological risks of heavy metals were then evaluated by risk assessment code.The experimental data indicate that the soil was heavily polluted by heavy metals,especially by Cd and Zn（ 92. 6% and 75%）. The chemical speciation analysis of heavy metal showed the available content of Cd mainly existed in exchangeable form（ 31. 2%）. The available content of Pb,Cu and Zn were distributed mainly in acid extractable fractions and Fe / Mn oxide fractions（ 27. 9%,30%and 27. 2%）,and Hg,As,Cr was mainly associated with residual fraction（ 90. 4%,72. 9% and76. 8%）. The results of risk assessment code showed Cd was medium and high risk（ 45. 6% and54. 4%）,Zn was medium risk（ 100%）,Cu was low and medium risk（ 41. 2% and 58. 8%）,Hg was mainly no risk（ 97. 1%）,As and Pb was mainly low risk（ 92. 6% and 91. 8%）. All the results indicated that the studied area was heavily polluted by heavy metals. The potential ecological risk of Cd was at very high level,while that of Zn and Cu was at a high level.