大气沉降及土壤扬尘对天津城郊蔬菜重金属含量的影响

为探究土壤重金属污染对蔬菜中重金属含量的影响,并分析蔬菜中重金属的主要来源,以天津城郊存在土壤重金属镉(Cd)超标风险的蔬菜基地为对象,施用特制含锌(Zn)、含锰(Mn)商品有机肥,对土壤和当地常见叶菜类蔬菜(油菜、芹菜、大白菜、生菜、葱)中重金属含量进行了测定.结果显示,该蔬菜基地土壤重金属有效性低,蔬菜中重金属含量均符合国家食品安全标准,施用含Zn、含Mn有机肥对蔬菜重金属含量无显著影响.针对蔬菜基地可能的重金属污染来源,监测了蔬菜基地周边大气沉降物重金属含量,对比监测清洗蔬菜与未清洗蔬菜的重金属含量,并通过计算蔬菜样品中重金属含量与钛(Ti)含量的比值关系,估算大气沉降和土壤扬尘对蔬菜样品重金属含量的贡献.结果表明,大气沉降和土壤扬尘对蔬菜中镉(Cd)、砷(As)、铅(Pb)、铬(Cr)的贡献率分别达到33.7%、83.7％、72.8％和71.0％,该地区蔬菜中的As、Pb、Cr主要来自吸附于表面的大气沉降和土壤扬尘,食用前仔细清洗能有效减少蔬菜中重金属含量.由此可见,从控制蔬菜重金属污染源头的角度分析,当地应优先监控大气沉降带来的蔬菜重金属污染风险.

Effects of Atmospheric and Dust Deposition on Content of Heavy Metals in Vegetables in Suburbs of Tianjin

Soils in the suburban vegetable fields in China may have a high risk of heavy metal contamination. A field experiment was conducted in a vegetable field with an elevated cadmium content in the soil near Tianjin to investigate the effects of zinc and manganese fertilizers on cadmium uptake by different leafy vegetables and to estimate the contribution of atmospheric and dust deposition on heavy metal content in vegetables. Results showed that the availability of cadmium and other heavy metals in the soils was low and all vegetables produced met the national food safety standards for heavy metals. Furthermore, applications of organic fertilizers enriched with either zinc or manganese had no significant effects on heavy metal content in the vegetables. Three methods were used to investigate the possible sources of heavy metal contamination in vegetables, including monitoring atmospheric deposition, comparing heavy metal content in washed and unwashed vegetables and calculating the relationship between heavy metals and titanium content in vegetables. Results showed that atmospheric deposition and soil dust contributed to 33.7%, 83.7%, 72.8% and 71.0%, respectively, of the total content of cadmium, arsenic, lead and chromium in unwashed vegetables. Washing significantly reduced heavy metal content in vegetables. Therefore, priority should be given to monitoring heavy metal contamination in vegetables caused by atmospheric deposition.