不同粒径地表街尘中重金属在径流冲刷中的迁移转化

Migration and Transformation of Heavy Metals in Street Dusts with Different Particle Sizes During Urban Runoff

在我国快速城市化进程中,街尘及其径流冲刷引起的重金属污染日显突出.通过对北京市城乡道路街尘及其人工降雨模拟径流冲刷过程中不同粒径街尘中重金属的分析,探讨街尘与径流冲刷过程中的粒径效应及不同重金属赋存形态的动态变化规律.结果表明,同一粒径颗粒物从"静态"街尘到"动态"径流中的颗粒物,重金属浓度呈下降趋势.街尘中重金属在径流冲刷过程中,存在溶解与解析现象,颗粒物粒径越小,减少比率越大,5种重金属(Cr、Cu、Ni、Pb、Zn)的减少比率分别为24.3%、56.8%、34.3%、22.8%、27.3%.街尘中的弱酸可提取态比例要略大于径流颗粒物中弱酸可提取态比例,部分以水溶态进入水体中.在径流冲刷过程中,水相溶解态重金属变化不大,水相颗粒态重金属含量随降雨时间径流过程迅速降低.固相颗粒物的重金属浓度随降雨时间总体上呈下降趋势.粒径越小,冲刷率越大,最大为62.1%,最小为4.6%.地表街尘在径流冲刷过程中,小粒径颗粒物具有较强的迁移能力,较容易进入水体造成污染.

The heavy metal pollution in runoff caused by street dust washoff has been an increasingly prominent problem in the context of rapid urbanization in China.Based on measurement of heavy metal contents in street dusts with different particle sizes and an experiment of street dust washoff using simulated rainfall,we analyzed the role of particle size of street dust in heavy metal pollution,and the variation in geometrical forms of heavy metals during street dust washoff.Our results showed that the heavy metal concentration decreased from ＂static＂ street dust to ＂dynamic＂ runoff particulate in the same diameter particles.Heavy metals in street dust were dissolved and extracted during washoff.The average loss proportion of the five metals（Cr,Cu,Ni,Pb,Zn） were 24.3%,56.8%,34.3%,22.8%,27.3%,respectively.The loss proportion increased with the decrease of the particle size of street dust.Proportion of extracted form dust was higher in street than that in washoff samples,which suggested some dissolved loss in water.In washoff samples,dissolved metals of waterphase did not have significant changes;however,heavy metals with particle state in waterphase reduced rapidly during runoff.Meanwhile,heavy metals of solid-phase particle reduced during runoff.Street dust with small particle size had higher loss rate during runoff.The variation rate of street dust loss among different particle sizes varied from 4.6% to 62.1%.Street dust with smaller particle size had higher migration ability in runoff,which was more risky to urban water pollution.