长期污灌农田土壤重金属污染及潜在环境风险评价

以西安市某典型污灌区农田土壤为研究对象,分析长期污水灌溉对表层土壤重金属含量及富集状况的影响,采用内梅罗指数法和Hakanson潜在生态危害指数法对其污染现状及潜在环境风险进行评价。结果表明：长期污灌已导致农田土壤Cd、Cr、Cu、Hg、Ni、Pb和Zn7种重金属相对自然背景有不同程度累积,其富集比例依次为100%、82.69%、100%、100%、80.77%、98.08%和100%,仅有土壤As平均含量低于其背景水平;以国家土壤环境质量标准二级限量值作为污染评价阈值,其中Cd和Hg污染表现突出,按其污染指数平均值排序为Cd〉Hg〉Ni〉Cu〉Zn〉As〉Cr〉Pb;土壤重金属综合潜在环境风险为＂强＂等级,Hg、Cd的环境影响占据主导;随污灌年限增长,离灌渠越近,农田土壤重金属的污染水平和环境风险越高。鉴于该区土壤重金属已呈现较强生态危害性,应及时采取必要防治措施,调整土地利用结构,确保农田环境及农产品安全生产。

Pollution and Potential Environment Risk Assessment of Soil Heavy Metals in Sewage Irrigation Area

In a typical sewage irrigation area, 52 surface soil samples were collected to determine total concentrations of arsenic （As）, cadmi- um（Cd）, chromium （Cr）, copper （Cu）, mercury （Hg）, nickel （ Ni ）, lead （Pb） and zinc （Zn）. The Nemero Synthesis Index and nakanson＇ s Environment Risk Index of soil heavy metals were evaluated and compared at different wastewater irrigation histories and distances from irri- gation canal. The results showed that some soil heavy metals had been enriched in the topsoil due to long-term sewage irrigation. The mean concentrations of As, Cd, Cr, Cu, Hg, Ni, Pb and Zn were 9.88 mg.kg-1, 1.45 mg·kg-1, 88.41 mg·kg-l, 52.24 mg.kg-1, 1.38 mg·kg-1, 34.14 mg· kg-1, 55.01 mg. kg-1 and 151.16 mg· kg-1, respectively. In nearly half of samples, Cd and Hg concentrations have exceeded the pollution levels based on Chinese Environment Quality Standard for Soils, which have exhibited a very serious pollution trend. Based on the pollution index of eight elements, they followed ： Cd〉Hg〉Ni〉Cu〉Zn〉As〉Cr〉Pb. In addition, there existed extremely strong comprehensive environment risks for soil heavy metals, in which slight-strong ecological risk for Cd and strong ecological risk for Hg. The risk order of soil heavy metals is Hg〉Cd〉Pb〉Cu〉As〉Ni〉Cr〉Zn. The comprehensive pollution index and ecological risk index of heavy metal increased with the increasing sewage irrigation histories and decreasing distances from irrigation canal. It is concluded that long-term wastewater irrigation was harmful to the ecological environment of farmland soils. In order to protect agricultural production safety and promote soil resource sustainable utiliza- tion, some necessary measures against soil heavy metal pollution in sewage irrigation farmland should be taken as soon as possible.