锌冶炼区耕地土壤和农作物重金属污染状况及风险评价

Heavy Metal Contamination of Soils and Crops near a Zinc Smelter

对贵州省某典型锌冶炼区耕地土壤和主要谷类农作物(稻米、玉米和小麦)进行取样调查,测定了土壤和谷类农作物中重金属Pb、Cd、Zn和Cu的含量,采用单因子污染指数和综合污染指数法评价了土壤和作物籽粒中重金属的污染状况,并分别采用潜在生态风险指数(RI)和危险商(HQ)法评价了土壤重金属污染的潜在生态风险程度和作物中重金属对成人和儿童的健康风险.结果表明:(1)冶炼区耕地土壤受到了重金属不同程度的污染,污染程度排序:玉米地>水稻田>小麦地,且Cd>Cu>Zn>Pb,内梅罗综合污染指数分析结果表明,玉米地污染程度为重污染,水稻田和小麦地为轻污染,且均以Cd对综合指数的贡献最大;(2)土壤Cd存在极强生态风险,4种重金属潜在生态危害大小顺序为:Cd>Pb>Cu>Zn;生态风险指数(RI)研究结果表明,研究区处于轻微、中等、强的和很强的生态风险程度的采样点比例分别为1.41%、21.1%、35.2%和42.3%.(3)冶炼区农作物稻米中重金属Pb、Cd、Zn、Cu的平均含量分别为0.145、0.017、16.97和2.704 mg·kg^(-1);玉米中重金属Pb、Cd、Zn、Cu的平均含量分别为0.094、0.055、26.81和4.464 mg·kg^(-1);小麦中重金属Pb、Cd、Zn、Cu的平均含量分别为0.048、0.085、35.37和5.426 mg·kg^(-1).(4)研究区稻米、玉米和小麦均存在重金属超标现象,重金属污染程度为小麦最重,稻米和玉米的污染程度相当,稻米和玉米污染等级均为安全,小麦处于警戒线.(5)各重金属元素每日摄入量均低于美国环保署的参考暴露剂量,安全性较好,但食用该区域谷类农作物引起复合重金属污染对成人和儿童均存在健康风险.(6)耕地土壤重金属含量与谷类农作物可食部分重金属含量间无明显相关性.

To evaluate the influence of mining activities on heavy metal contamination and health risks in a zinc-smelting area in Guizhou Province,Pb,Cd,Zn,and Cu in agriculture soils and dominant crops were monitored and analyzed. A single factor pollution index and a comprehensive pollution index were calculated to assess the quality of soils and crops. Furthermore,the potential ecological risks of the four heavy metals in soils and crops were evaluated using the potential ecological risk index（ RI）. The potential health risks to adults and children induced by the intake of these heavy metals through consumption of crops were evaluated using the hazard quotient（ HQ）. The results showed that：（1） The farmlands in the zinc-smelting area were contaminated by heavy metals; the most polluted farm land was corn fields followed by paddy fields and wheat fields. The order of the heavy metal concentrations was Cd Cu Zn Pb. The Nemero index of corn fields was higher than the threshold value of heavy pollution and was higher than that of the paddy and wheat fields. Cd contributed most to the integrated pollution index.（2） The very high ecological risk was posed by Cd followed by Pb,Cu,and Zn. The results of the potential ecological risk assessment showed that 1. 41% of the sites were classified as low risk,21. 1% classified as medium risk,35. 2% as high risk,and 42. 3% as extremely high risk.（3）The average concentrations of Pb,Cd,Zn,and Cu in rice were 0. 145,0. 017,16. 97,and 2. 704 mg·kg^-1,respectively. The average concentrations of Pb,Cd,Zn,and Cu in corn were 0. 094,0. 055,26. 81,and 4. 464 mg·kg^-1,respectively. The average concentrations of Pb,Cd,Zn,and Cu in wheat were 0. 048,0. 085,35. 37,and 5. 426 mg·kg^-1,respectively.（4）Rice,corn,and wheat from the study area were subjected to pollution at different degrees. Among the three crops studied,wheat was polluted most heavily,followed by rice and corn.Contamination levels of rice and corn were safe,whereas the contamination of wheat reached alarming levels.（5） The daily intake of individual heavy metals from food was below the standard exposure dose set by the United States Environmental Protection Agency. In addition,the assessment results for the comprehensive health risk index for the three crops indicate that the contamination of heavy metals poses health risks to adults and children by food ingestion.（6） Positive correlations were not observed between farmlands and crops.