覆膜对莴苣中重金属的影响及健康风险评价

Effects of Film Mulching on Heavy Metals in Lettuces and Health Risk Assessment

通过田间对比试验,采用逐级提取技术,研究覆膜栽培方式对莴苣茎和叶中Cu、Fe、Cd总量和形态的影响及其健康风险评价。相比于不覆膜方式,覆膜栽培方式促进了土壤有机质的矿化和莴苣的生长,改变了重金属Fe和Cd向莴苣迁移的行为。覆膜方式对莴苣茎和叶中Cu的总量影响很小,但显著增加了莴苣茎中的Cd含量,降低了叶片中Fe的含量,平均增值为0.2 mg/kg和-150 mg/kg。形态分析结果表明覆膜栽培使莴苣茎中的水提取态Fe向盐酸提取态Fe转化,降低了其在茎中的生物活性,由此导致叶片部位总Fe以及盐酸提取态Fe和残渣态Fe的减少。覆膜组茎中Cd的活性并没有改变,其总Cd的增加归功于活性最低的残渣态含量的增加;而叶片中显著增加的乙醇提取态Cd由于占总量的比例很少,因此覆膜组叶片中总Cd并没有显著增加。参照食品安全国家标准,2种栽培方式下的莴苣叶中Cd总量均超标,存在食品安全问题,但以每日最大允许摄入量作为参考,莴苣各部位中3种元素的人均日暴露量均低于WHO推荐的ADI值2.4、42、0.06 mg/d。覆膜栽培方式对人体莴苣叶摄入量贡献率的影响较大,使Fe的贡献率降低了13.1%,而Cd的贡献率增加了6.53%,即增加了摄入Cd的潜在风险。

Field experiments were conducted and sequential extraction technique was used to compare the effects of plastic film mulching（PFM） on total amount,fraction distribution of Cu,Fe,Cd and their risks to human health in lettuces were assessed. Compared with open field,PFM promoted the mineralization of SOM obviously and growth of lettuces slightly,altered transfer of Fe and Cd from soil to lettuces. PFM increased content of Cd by 0.2 mg/kg in lettuce stems,almost unchanged the total amount of Cu in lettuces,but decreased content of Fe by 150 mg/kg in lettuce leaves. Result of speciation analysis showed that PFM increased the transfer of Fe from water-extractable Fe to hydrochloric acid-extractable Fe in stems,therefore decreased the bioactivity of Fe in lettuce stems,and resulted in decreases of amount of total Fe,fraction hydrochloric acid-extractable Fe and residue Fe in lettuce leaves. In PFM group,the bioavailability of Cd in lettuce stems were unchanged,and the increase of total Cd in lettuce stems was attributed to the increasing of the amount of the residue fraction Cd. The obviously increasing of fraction ethanol-extractable Cd did not cause significant increase of Cd amount in lettuce leaves in PFM because of its low concentration relative to total Cd. The contents of Cd in leaves in two cultivations were both beyond the national standard of food security. However,daily exposure dose of Cu,Fe,Cd were lower than the maximum allowed daily intake reference of 2.4 mg/d,42 mg/d,0.06 mg/d respectively. The plastic film mulching produced great effects on intake contribution for lettuce leaves,decreasing contribution rate of Fe by 13.1%,but increasing contribution of Cd by 6.53%,which indicated that PFM increased the potential risk to human health of Cd.