典型河谷城市儿童土壤与灰尘铅暴露风险

Assessing Exposure Risk of Lead in Urban Soil and Dust to Children in the Valley-city

为定量评价河谷型城市土壤与灰尘铅对城市儿童健康的影响与风险,结合野外调查的基础上,以陕西渭河谷地典型工业城市宝鸡、西安、渭南和铜川为研究区域,以定量分析河谷型城市儿童环境铅暴露为核心,收集4个城市土壤与灰尘分析样品总计243个。利用X射线荧光光谱法测定了4个城市土壤与灰尘铅的含量;采用BCR连续形态分级法探究了城市土壤与灰尘重金属铅地球化学形态分布与迁移特征;根据US EPA污染物暴露与健康风险评价模型对城市儿童铅暴露进行了评价。研究结果表明渭河谷地典型城市宝鸡、铜川、西安和渭南城市土壤与灰尘铅浓度(X±SD)分别为(409.2±52.54)和(624.70±66.15)mg·kg-1、(357.47±41.37)和(592.60±36.78)mg·kg-1、(61.4±13.31)和(78.42±14.89)mg·kg-1、(46.71±12.11)和(64.7±13.76)mg·kg-1,均高出陕西省土壤铅背景值;污染水平依次为宝鸡>铜川>西安>渭南。4个河谷型城市土壤与灰尘重金属铅发生整体迁移的趋势为:宝鸡城市灰尘(90.71%)>西安城市灰尘(84.74%)≥宝鸡城市土壤(83.12%)>渭南城市灰尘(74.89%)≥西安城市土壤(74.50%)>铜川城市灰尘(72.49%)>铜川城市土壤(57.50%)>渭南城市土壤(53.79%)。可见,铅在均在城市灰尘中的迁移趋势远大于相应的城市土壤。4个城市土壤与灰尘均表现出较大的儿童暴露致癌风险,宝鸡和铜川城市儿童土壤与灰尘铅暴露也分别存在非致癌风险,风险程度依次为宝鸡>铜川>西安>渭南。儿童铅暴露致癌与非致癌风险程度与其城市土壤和灰尘中铅可氧化态分布呈相似的规律,表明碱性的城市土壤与城市灰尘(p H>7)中可氧化态铅可能是导致河谷型城市儿童铅暴露风险和儿童血铅污染的主要形态和因素。由此,城市燃煤排放与含铅制品的加工等活动可能是渭河谷地河谷型城市儿童血铅与铅暴露最主要的贡献源,必须采取长期有效的监测与控制措施。

To quantificationally assess the health risk of children exposure to the heavy metal lead from urban soil and dust in the valley-city, a total of 243 analytical samples composited from 3-5 subsamples according to classical cone and quarter technique were collected from the 0-20 cm top soil and 1-1.5 m high building balcony dust in Baoji, Xi＇ an, Weinan, Tongchuan industrial areas. The concentrations of heavy metal lead including of its chemical fractionations and health risks exposure to children were investigated by XRF, BCR and USEPA health risk assessment methods respectively. The results showed that the concentrations of lead in urban soil and dust in Baoji, Xi＇ an, Weinan, Tongchuan were （409.2 ±52.54） and （624.70 ± 66.15） mg .kg-1, （357.47 ±41.37） and （592.60 ±36.78） mg＇kg1, （61.4 ± 13.31） and （78.42 ± 14.89） mg.kg-1, （46.71 ± 12.11） and （64.7 ± 13.76） mg.kg-1 respectively, which was much beyond the background value of lead in Shaanxi Province. The corresponding pollution levels divided by background value decreased as the order of Baoji 〉 Tongchuan 〉 Xi＇ an 〉 Weinan. The BCR analysis suggested that the mobility tendency of lead in urban soil and dust decreased as the following order： urban dust of Baoji （90.71%） 〉 urban dust of Xi＇ an （84.74%）≥urban soil of Baoji （83.12%） 〉 urban dust of Weinan （74.89%）≥ urban soil of Xi＇ an （74.50%） 〉 urban dust of Tongchuan （72.49%） 〉 urban soil of Tongchuan （57.50%） 〉 urban soil of Weinan （53.79%）. The migration trend of lead in urban dust was much larger than corresponding urban soil. On the other hand, the hazard indexes （HI） of lead in urban soil and dust between Baoji and Tongchuan city were higher than 1, indicating that lead posed a higher non-carcinogenic risk to children in two cities. However, the carcinogenic risk of lead exposure to four urban children obtained in this study had a considerable level, and the risk degree decreased as Baoji 〉 Tongchuan 〉 Xi＇ an 〉 Weinan. The noncarcinogenic and carcinogenic risk degrees of lead exposure to children show the similar trend with the oxidizable fractionation distributing in four corresponding urban soil and dust, which indicated that the oxidizable fractionations of lead might be the mail speciation and factor causing to children＇ s blood lead poisoning. Therefore, the anthropic activities including the industrial discharge and coal combustion were the main sources exposure to children in the Weihe Basin. A comprehensive environmental management strategy should be concerned by the local government to address lead pollution in urban areas.