酸与Cd污染农田的植物修复及健康风险评价

Phytoremediation and Health Risk Assessment of Acidified and Cadmium Contaminated Farmland

在广西环江县酸与Cd复合污染土壤的大田条件下,研究种植超富集植物龙葵(Solanum nigrum L.)和经济作物甘蔗(Saccharum officinarum L.)对污染农田土壤的治理和修复效果,并分析龙葵和甘蔗对人体的健康风险。植物修复材料研究结果表明,龙葵中Cd的最高含量可达16.83 mg·kg-1(试验区土壤Cd含量0.71 mg·kg-1),富集系数大于1,表现出良好的Cd富集植物特性;甘蔗中Cd的最高含量为0.54 mg·kg-1,富集系数小于1。若按当地正常种植模式计算,龙葵从土壤中提取Cd的量可达100 g·hm-2以上,提取效率达6%以上,通过种植龙葵将试验区的土壤Cd修复到GB 15618—1995《土壤环境质量标准》的二级标准限值以内最短只需9年左右。因此,种植龙葵对当地酸与Cd复合污染土壤的治理和修复是可行的。试验区土壤中Cd含量分析结果表明,不同土壤处理模式下,添加石灰和氢氧化钠处理龙葵修复效率最高,可达4.44%。对植物的食用健康风险分析结果表明,将龙葵作为蔬菜食用,其可食用部位的Cd含量为5.21~6.83 mg·kg-1(干重),远远超出食品安全国家标准GB 2762—2012《食品中污染物限量》限值,当地居民平均每日摄入Cd的量为5.38~17.39μg·kg-1·d-1(鲜重),超出FAO/WHO提出的重金属Cd人均每日允许摄入限量标准(PTDI),引起的重金属暴露风险指数大于1,具有较高的潜在风险,因而当地居民不宜继续食用;食用实验区种植的甘蔗生产的蔗糖引起的重金属暴露风险指数小于1,但由于蔗糖中Cd的含量均超出国家标准限值,具有一定的健康风险,需改变甘蔗综合利用方式。

In this paper, remediation of farmland polluted by acid and cadmium(Cd)using hyperaccumulator, Solanum nigrum L. and cash crop, sugarcane(Saccharum officinarum L.), was investigated in Huanjiang county of Guangxi. The human health risk of both plants was also assessed. Solanum nigrum accumulated Cd up to 16.83 mg·kg-1in the plant, with Cd accumulation coefficient greater than 1. Sugarcane had the highest Cd of 0.54 mg·kg-1, with Cd accumulation coefficient less than 1. Under the local normal cropping system, amount of Cd extracted by S. nigrum from soil was estimated to be more than 100 g·hm-2, with Cd phytoextraction rate of more than 6%. It would take about9 years to reduce soil Cd to the GradeⅡ level in the National Environment Quality Standards for Soils(GB 15618—1995)by planting S. nigrum. Therefore, it is feasible to remediate farmlands contaminated by acid and cadmium through planting S. nigrum. Applying lime and sodium hydroxide led to a greatest reduction of total Cd in soil grown with S. nigrum, which was 4.44%. Cadmium concentrations in the edible parts of S. nigrum ranged 5.21~6.83 mg·kg-1much higher than the standard of the National Food Safety(GB 2762—2012). If this S. nigrum were used as a vegetable, the average daily amount of Cd intake by local would be 5.38~17.39 μg·kg-1·d-1(fresh weight), far beyond the Provisional Tolerable Daily Intake(PTDI)for Cd proposed by FAO/WHO, with the risk index of heavy metal exposure greater than1. The results indicate that the currently grown S. nigrum should be not used for vegetable. Although, the risk index of Cd exposure for consuming sucrose from the experimentation area was lower than 1, the concentrations of Cd in the sucrose were higher than the standard of the National Food Safety. Attention should be paid to the way of sugarcane comprehensive utilizations.