小麦籽粒铅污染来源的同位素解析研究

以中国西北地区某工业区为研究区域,采集大气降尘、耕层土壤样品(0～20 cm),及对应农田位置的小麦籽粒样品,用电感耦合等离子质谱(ICP-MS)测定铅元素质量比及铅同位素比率值。运用普通块克里金法(Ordinary Kriging)预测大气铅沉降通量分布、耕层土壤和小麦籽粒铅质量比空间分布;结合二元混合模型计算各污染源对小麦籽粒铅质量比的贡献率。结果表明:1)耕层土壤铅质量比范围为21.8～40.0 mg/kg,平均值为27.1 mg/kg,高于当地土壤背景值(21.4 mg/kg),说明耕层土壤受到一定程度的污染。2)研究区域小麦籽粒铅质量比范围为0.269～0.768 mg/kg,平均值为0.430 mg/kg,超标率达100%。3)大气降尘和耕层土壤对小麦籽粒铅质量比的贡献率分别为90%～99%和1%～10%。通过研究耕层土壤和小麦铅污染的范围及程度,探讨小麦籽粒铅污染的来源,解析各污染源的相对贡献率,可为制定控制食品中重金属污染,保障食品安全措施提供依据。

Isotope analysis of lead pollution sources in wheat kernel

To identify and apportion the contributions of lead pollution sources in wheat kernel, the surrounding area of a lead-zinc smelter in northwestern China was taken as the study area, local atmospheric deposits, tilled soils (0-20 cm), and the corresponding wheat samples were collected and then lead concentrations and isotope ratios was analyzed by ICP-MS . The spatial distribution of atmospheric lead settlement fluxes as well as lead concentrations in soil and wheat kernel were predicted by Ordinary Krigging methods. The contributions of lead pollution sources to wheat kernel were calculated with a linear mixing model. The results showed that lead concentrations in tilled soil ranged from 21.8 to 40.0 mg/kg, and the average level (27.1 mg/kg) was higher than background value (21.4 mg/kg) of local soil samples, which indicated that the soil in local area was polluted slightly. The lead concentrations of wheat kernel in the canyon ranged 0.269-0.768 mg/kg, of which the average level was 0.430 mg/kg, and 100% of the wheat samples exceeded the maximum level in GB2762-2005. The contributions of atmospheric deposits and tilled soil to lead concentrations in wheat kernel were 90%-99% and 1%-10%, respectively. The paper provided scientific basis for making policy on heavy metal contamination control and food safety production system.