杭州市土壤铅污染的铅同位素示踪研究

LEAD ISOTOPES IN SOIL AS A TRACER OF ENVIRONMENTAL LEAD POLLUTION IN HANGZHOU

根据杭州市40个土壤全铅和38个可溶相铅的统计分析,土壤中全铅平均含量为49.6×10-6,可溶相铅平均为21.4×10-6,城区表土的全铅高达76.1×10-6,显著高于全国土壤平均值。分析结果还显示,从农村→远郊→近郊→公路旁,土壤可溶相铅含量逐渐增加,且土壤的可溶相铅含量与深度具明显的负相关关系。表明杭州市土壤受到了不同程度的铅污染,污染程度由农村→远郊→近郊→公路旁→城区有明显的增高趋势。通过对茶园土壤中可溶相铅、残渣态铅及城区表土全铅的同位素组成对比分析发现,从土壤残渣态(代表土壤背景)→土壤可溶相→城区表层土壤全铅206Pb/207Pb比值有明显的降低。208Pb/(206Pb+207Pb)也有类似的变化趋势。将土壤与杭州市的汽车尾气、大气等环境样品进行对比发现,随着土壤受污染程度的增加,铅同位素组成逐渐向汽车尾气铅漂移,表明汽车尾气排放的铅为其主要污染源。

According to the statistical analysis of 40 entire lead and 38 dissoluble lead data of the soil samples in Hangzhou, the averages are 49.6×10 -6 for entire lead and 21.4×10 -6 for dissoluble lead respectively. In addition, the data show that the dissoluble lead contents in the soils increase from countryside→outer suburb→suburb→the highway nearby and decrease with depth in vertical profile, which indicates that the soils in Hangzhou are suffered from lead pollution and the pollution degrees have an increasing trend from countryside → outer suburb → suburb → highway nearby. Through comparing the isotopic compositions of the residual phase lead (RPL, on behalf of the soil background) with those of the dissoluble lead (DL) in tea gardens and with those of the entire lead in the urban surface soils (ELUSS), we can find that the 206Pb/ 207Pb ratios decrease obviously from RPL to DL to ELUSS, the 208Pb/( 206Pb+ 207Pb) ratios also have similar tendency. Comparison of soil lead compositions with those of environmental samples, such as automobile exhaust, aerosols and floating dust, reveals that lead isotopic ratios gradually shift to automobile exhaust lead with the pollution degrees increasing, which suggests that the traffic-derived lead be the main source of pollution.