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街尘是存在于城市不透水地面上的固体颗粒物[1],具有单体粒径小、质量轻、易在环境中迁移扩散的特性,可吸附来自工业、交通、家庭排放、大气颗粒物沉降等多种来源[2-5]的污染物,且能通过皮肤接触、口鼻摄入等方式[6-7]进入人体,对环境和城市居民健康构成极大危害[8]. 锑及其化合物是一类具有基因毒性的有害物质[9]. 细颗粒街尘被吸入人体,藏于其中的锑与红细胞膜中的—SH基团相互作用[10-11],严重时损伤肝脏和肾脏,甚至威胁生命安全.
汽车刹车片使用Sb2O3作为摩擦材料和框架阻燃剂,Sb2S3作为润滑剂,含量在1%—5%左右[12-13],被认为是城市街尘中锑污染物的主要来源[14]. 通过测定与车辆制动过程相关的街尘中重金属锑及其形态的含量,可有效评估锑排放的大小及存在形式. 当下国内外关于城市街尘中锑污染的研究主要集中在总量而非形态分布. 然而,锑的毒性和流动性强烈依赖于其化学形态[15],分析锑各形态的含量更能对环境中锑的生物可利用性、迁移转化能力以及潜在毒性进行准确客观的评价. 粒径<97 μm的街尘可长时间悬浮在大气中,也被称为再悬浮粉尘,容易随风迁移造成范围更广的污染,且易被城市居民通过口鼻摄入,是城市居民接触到重金属的主要途径[16-18];粒径<63 μm的街尘不仅可被口鼻吸入,还被证实仅有小于此粒径的街尘能被黏附在皮肤上[19],手-口活动更多的儿童特别容易摄入大量的此类细小灰尘[20],其质量占比虽小,却具有更强的重金属负载能力,约占总金属负载量的25%—60% [21-22]. 此外,城市不同区域人为活动和交通密度不同对锑排放也会产生影响. 因此,分功能区和粒径对城市街尘中总锑和锑形态分布进行研究就显得十分必要.
成都位于四川盆地西部,东经102°54′—104°53′和北纬30°05′—31°26′之间,地理位置特殊,且处于亚热带湿润季风气候区,常年积云积雨,不利于污染物的扩散. 作为超大型城市,截止2021年,该市常住人口为2093.8万人,汽车保有量超500万辆,仅次于北京,交通排放对于环境造成的污染引人瞩目. 目前,尚未有关于高交通量城市街尘中锑含量及赋存形态的研究,因此,本文选取成都市作为研究对象,分4个功能区、32个采样点采集街尘样品,测定不同功能区不同粒径下总锑及各赋存形态锑含量,计算地累积指数、富集因子和生态风险等级,分析街尘中总锑与各形态锑分布特征、污染程度、生态风险及其可能的原因,为相关部门制定刹车片锑含量标准和城市环境锑污染治理提供数据支持.
成都市中心城区街尘中锑形态分布及生态风险评价
Distribution of antimony species in street dust in downtown Chengdu and its ecological risk assessment
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摘要: 为了解汽车排放对城市街尘中锑赋存形态的影响及可能造成的污染和生态风险,选择汽车保有量全国第二的成都市中心城区街尘为研究对象,采用沸水浴王水加热法和改进的BCR法对4个功能区两个粒径(<97 μm和<63 μm)的样品分别进行总量消解及形态提取,以HG-AFS进行锑的测定并计算各自的含量,再运用地累积指数法、富集因子法和风险评价编码法(RAC)对其污染程度和生态风险进行评价. 结果表明,粒径<97 μm和<63 μm的街尘中,总锑含量介于1.221—9.589 mg·kg-1之间,均超出成都市浅层土壤环境地球化学背景值和中国A层土壤背景值;4个功能区锑平均含量大小为交通区>商业区>居民区>教育区. 4个形态中,锑残渣态平均含量占比最高,弱酸提取态和可还原态次之,可氧化态最低;粒径更小的街尘中弱酸提取态占比相对较大,说明小粒径街尘锑的生物可利用性更高. 地累积指数和富集因子法计算结果均表明,交通区锑污染最为严重;风险评价编码法结果表明,所有采样点均处于低生态风险,但有一些采样点逼近中等风险.Abstract: In order to understand the impact of automobile emissions on the speciation distribution of antimony in urban street dust and the possible pollution and ecological risks, the samples were taken in downtown Chengdu, which has the second-largest automobile population in China. The samples, with two particle sizes (<97 μm and<63 μm) and from four functional areas, were digested using aqua regia in a boiling water bath for total antimony and extracted using the modified BCR method for Sb species. The determination of antimony was performed with HG-AFS and the respective content was calculated. The pollution degree and ecological risk were evaluated using the geo-accumulation index, the enrichment factor and risk assessment code (RAC) methods, respectively. The results showed that the total contents of antimony in the dust with two particle sizes (< 97 μm and < 63 μm) were in the range of 1.221—9.589 mg·kg-1, which exceed the geochemical background value of the shallow soil environment in Chengdu and soil background value of layer A in China. The order of the average antimony content in four functional areas is traffic area> commercial area> residential area > education area. Among the four fractions, the proportion of the average content of residual antimony is the highest, followed by the weak-acid extractable and reducible, and the oxidizable is the lowest. The proportion of weak-acid extractable in street dust with smaller particle sizes is relatively larger, indicating that the bioavailability of antimony, in this case, is higher. The calculated results of the geo-accumulation index and enrichment factor showed that antimony pollution in the traffic area was the most serious and the risk assessment code showed all samples were at low ecological risk, with some samples approaching medium risk.
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Key words:
- antimony /
- speciation /
- contamination evaluation /
- street dust /
- particle size /
- functional area.
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表 1 各功能区街尘中锑的含量
Table 1. Antimony content in street dusts from different functional areas
粒径
Particle size区域
Area最小值/(mg·kg−1)
Minimum最大值/(mg·kg−1)
Maximum平均值/(mg·kg−1)
Mean标准差/(mg·kg−1)
Std.dev变异系数/%
CV样本量
Sample size<97 μm 交通区 5.123 9.589 6.260 1.498 23.92 8 教育区 1.221 7.206 3.862 1.627 42.12 8 居住区 3.013 7.956 4.724 1.529 32.37 8 商业区 4.042 6.344 5.014 0.915 18.26 8 汇总 1.221 9.589 4.965 1.607 32.37 32 <63 μm 交通区 5.542 9.286 7.068 1.390 19.67 8 教育区 1.693 5.936 4.337 1.407 32.44 8 居住区 3.024 7.019 5.011 1.547 30.87 8 商业区 4.251 6.658 5.347 0.751 14.04 8 汇总 1.693 9.286 5.441 1.612 29.63 32 -
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