贵州煤矿区成熟期水稻中重金属的分布特征及风险评价

Distribution and Food Exposure Risk Assessment of Heavy Metals Inmature Rice on the Coal Mining Area, Guizhou

污水灌溉已经成为解决缺水地区农业用水的重要途径,也是导致土壤重金属污染的重要因素,甚至威胁着农产品的安全。为了研究重金属在植物体内的分布特征及对人体的安全性,以贵州兴仁长期受污水(即酸性矿坑废水)灌溉影响的水稻为研究对象,分析成熟期水稻样品不同部位中Fe、Mn、Cu、Pb、Zn、Cd、Cr和Ni等重金属的含量变化及分布规律,同时以《食品安全国家标准食品中污染物限量》(GB 2762—2017)评价了糙米的安全性,并应用USEPA推荐的RfD值评估经食物链暴露的糙米重金属对成人和儿童所产生的健康风险。结果表明,除Mn、Zn和Ni外,水稻各器官(根、茎、叶、糙米)对Fe、Cu、Pb、Cd和Cr的积累能力为根>茎或叶>糙米,污灌区水稻根部富集的重金属高于对照区。采样区糙米中Pb、Cd、Cr的含量均超过食品安全标准的2~8倍,尤其Cr表现更为突出。以R_fD作为参考值的风险评价结果表明,污灌稻田供试糙米中重金属的日摄入量对成人及儿童均具有潜在的危害,且成人平均日摄入的Pb、Zn、Cd、Cr、Ni的量是相应元素R_fD值的2、1.3、5、31及6.2倍,表现出Cr的食物暴露风险最大,而Pb、Cd、Ni的暴露风险中度。为了研究区的食品安全及人体健康,除了需对灌溉用水进行处理外,还需采用适当的方法去除土壤中的Cr和Cd等重金属。

Sewage irrigation has become an important approach to solve agricultural water utilization in water-deficient area.However,it is also an important factor for soil pollution because of the presence of heavy metals,which may further threaten the safety ofagricultural products.In order to understand the distribution characteristics of heavy metals in plants and its safety for human,the ricewhich irrigated by wastewater discharged from acid mine drainage in coal mining area in Xingren County,Guizhou Province wasstudied,and the levels and distributions of heavy metals(Fe,Mn,Cu,Pb,Zn,Cd,Cr and Ni)in the root,stem,leaf of rice wereinvestigated.It was found that the accumulation ability of root,stem,leaf and brown rice of detected heavy metals were in the trend ofroot>stem and/or leaf>brown rice,and higher levels of heavy metals in root irrigated by wastewater than those in control area.Basedon the national health food safety standards,the concentrations of Pb,Cd and Cr in brown rice were2~8times higher than thelimitation values.Moreover,according to the RfD values recommended by USEPA,the daily intake of metals(DIM)in brown ricegrown in the study area have adverse effect to adults and children,and the average DIM values for Cd,Cr,Ni were2,1.3,5,31and6.2times higher than the RfD values recommended,respectively.Cr posed significant exposure risk and Pb,Cd,Ni exposed moderate riskfor local adult and children.Therefore,to guarantee the food safety and human health,it is necessary to take appropriate approaches todislodge the heavy metals(such as Cr,Cd,etc.)in soil and apply pretreatment of irrigation water before reuse.