兰州城关区地表灰尘中Pb、Cr含量及其赋存形态分布研究

Contents and chemical speciation of Pb and Cr in the surface dusts taken from Chengguan district of Lanzhou

利用原子吸收光谱仪测定了兰州城关区地表灰尘中Pb、Cr含量,并采用Tessier连续提取法分析了其赋存形态分布。结果表明:(1)地表灰尘中Pb质量浓度以居民小区最高,Cr质量浓度以商业中心最高,分别达到120.36、108.10mg/kg。(2)兰州城关区地表灰尘中Pb、Cr平均值分别是甘肃省土壤背景值(17.9、69.3mg/kg)的5.34、1.35倍。总体来说,兰州城关区地表灰尘Pb、Cr含量处于国内中等偏下水平。(3)Pb、Cr在地表灰尘中主要以残渣态和铁锰氧化物结合态存在,各采样点平均值中Pb、Cr残渣态分别占75.33%、79.01%。(4)地表灰尘中Cr赋存形态分布规律与土壤中一致,因受工业污染影响较小,推测Cr主要来自土壤源,各采样点含量相近且略高于背景值的分布特点是由于甘肃省土壤Cr背景值本身较高造成的。(5)地表灰尘中Pb除公园绿地为轻度污染外,其他采样点均已达到中度污染水平;Cr总体处于无实际污染水平。结合Pb、Cr主要以残渣态为主的特点,总体来说,兰州城关区地表灰尘中Pb累积污染程度严重,Cr无污染。

The contents and chemical speciation of Pb and Cr in the urban surface dusts taken from the Cheng- guan District of Lanzhou were analyzed by the flame atomic absorption spectrometer and Tessier sequential extraction methods. The results showed that the highest concentrations of Pb （120. 36 mg/kg） and Cr （108. 1 mg/kg） were found in the residential and commercial areas,respectively. The contents of Pb and Cr in surface dusts of Chengguan District were separately 5.34 and 1.35 times of the soil background values in Gansu Province. However, they still lower the mediate level of China in general. The Pb and Cr in the surface dusts of Chengguan District mainly occurred in a residual and Fe-Mn oxides state, the percentages of residual Pb and Cr in the dusts were 75.33% and 79.01%, respectively. The fraction of Cr speciation in dust was similar with that in soil, and Chengguan District suffered little influence from industrial pollution, so it could be speculated that Cr in dust mainly contributed from soil. The Cr con- tent in different sampling sites was similar and slightly higher than the background value, this might caused by the relative high Cr backgroud value of Gansu. Pb in all sampling sites reached the moderate pollution levels except in park green space （in midle pollution level）. Generally speaking, the dusts in the Chengguan District of Lanzhou were mod- erately polluted by Pb and practically unpolluted by Cr.