西安市街尘中重金属赋存形态和污染特征分析

Chemical Forms and Pollution Characteristics of Heavy Metals in Urban Street Dust of Xi'an, China

城市街尘是重金属等污染物质的依附载体,居民日常活动频繁接触使得污染物很容易进入人体,对居民健康危害极大,因此街尘污染控制受到广泛关注。为了开展街尘重金属污染状况及特征研究,针对西安市街尘聚集量较多的冬春季节,选择不同路况特征的8个区域作为街尘样品采样点,运用Tessier顺序提取法对样品中的重金属元素进行分步提取,采用电感耦合等离子质谱仪(ICP-MS)测定了街尘中镉(Cd)、铅(Pb)、锌(Zn)、铜(Cu)、锰(Mn)、铁(Fe)等6种重金属元素的含量及赋存形态。与陕西省土壤重金属环境背景值对比显示:8个采样点处,街尘中6种重金属元素含量均显著超过环境背景值,平均超出倍数分别为Cd49.6倍、Pb15.7倍、Zn8.1倍、Cu3.8倍、Mn2.5倍、Fe2.3倍。偏差分析显示:Cd含量受采样点环境影响较大,Fe在各点处较为均衡,其他元素略有差异;主干路和次干路段街尘中的Cd、Pb和Zn富集较支路严重,沥青路面上Cd和Cu积累高于水泥路面而Pb和Zn低于水泥路面。赋存形态分析发现:西安市街尘中,Cu主要以有机物结合态赋存,Fe和Zn主要以铁锰结合态赋存,Mn主要以铁锰结合态和有机结合态赋存,Pb主要以可交换态和铁锰结合态赋存,Cd主要以可交换态及碳酸盐结合态赋存。道路等级越高,其街尘重金属的可交换态和碳酸盐结合态比例也越高;沥青路面上更容易产生或聚集可交换态和碳酸盐结合态重金属。各重金属生物有效性顺序为:Cd>Pb>Cu>Zn>Mn>Fe。

Urban street dust is the dependent carrier of heavy metals and other contaminants, and residents’ frequent contact with contaminants in daily activities make them easily enter the human body, which is of great harm to the health of residents, so street dust pollution control has attracted widespread attention. In order to study the status and distribution of heavy metal contamination of street dust, eight regions with different road surface characteristics were selected as street dust sampling points in winter and spring when street dust gathers abundantly in Xi’an. Tessier sequential extraction was used to extract the heavy metals in the sample, and ICP-MS was used to measure the content of Cu, Zn, Fe, Mn, Pb and Cd in street dust in different forms. The contrast with environmental background values of heavy metals in the soil in Shaanxi Province shows that the content of the six heavy metal elements in the street dust of all eight sampling points significantly exceeds background values, respectively 3.8, 8.1, 2.3, 2.5, 15.7 and 49.6 times, and the gathering of Cd, Pb and Zn in the dust of trunk and secondary streets is severer than branches. According to deviation analysis:the content of cadmium at each point had a greater influence on the environment, iron at each point is relatively balanced, other elements are slightly different at each point. The accumulation of Cd and Cu on the asphalt road surface is higher than concrete road surface, while that of Pb and Zn is lower. According to the occurrence form analysis, Cu in the street dust of Xi'an is mainly in the organic bound form; Fe and Zn is mainly in the ferro-manganese bound form; Mn exists in the ferro-manganese bound form and organic bound form;Pb mainly exists in the exchangeable form and ferro-manganese bound form;Cd mainly exists in the exchangeable form and carbonate bound form. The higher the street grade, the larger the proportion of exchangeable form and carbonate bound form of heavy metals. The asphalt road surface is more prone to production or accumulation of exchangeable form and carbonate bound heavy metals. Bioavailability of heavy metals is Cd>Pb>Cu>Zn>Mn>Fe.