西北地区典型城市PM_(2.5)中重金属污染特征及健康风险评价

Heavy metals in PM_(2.5) in four metropolitan cities in Northwest China:pollution characteristics and health risk assessment

目的了解西北地区4个典型城市PM_(2.5)中7种重金属元素的污染特征,评价PM_(2.5)中重金属对人群的健康风险。方法选取乌鲁木齐、西安、兰州和银川市作为西北地区的典型城市,收集PM_(2.5)中重金属浓度的文献作为数据来源,分析重金属的污染特征,采用健康风险评价模型对4个城市不同人群的健康风险进行评价。结果重金属元素的浓度水平存在地区差异,7种元素中Zn在4个城市中的浓度均为最高,As和Cr(VI)在4个城市中的年均值均高于参考限值,且As和Cr(VI)在西安市的浓度最高;Cd元素仅在乌鲁木齐市的年均值高于参考限值;4个城市的非致癌风险以Pb为主,但危险指数HI(hazard index)值均小于1,西安市的HI值最高;4个城市致癌风险以As为主,乌鲁木齐市As和Cr(VI)的终生致癌风险LCR(lifetime cancer risk)值均接近10^(-4),西安市As和Cr(VI)的LCR值均大于10^(-4),2个城市的终生总致癌风险ILCR(integrated lifetime cancer risk)值均超过阈值水平,其中西安市的ILCR值最高,而兰州和银川市的ILCR值均低于阈值水平。结论在纳入研究的4个城市中,西安市的致癌和非致癌风险均为最高,重金属污染最严重;乌鲁木齐市重金属污染也应受到重视,而兰州和银川市重金属的健康风险在人群可接受的范围内。

Objective To examine distribution characteristics of 7 heavy metal elements in particulate matter less than 2.5μm in aerodynamic diameter(PM_(2.5))and to evaluate health risk of the heavy metals in PM_(2.5)in four metropolitan cities in Northwest China.Methods Through literature retrieval,we extracted the data on heavy metals in PM2.5 samples collected under normal weather conditions in Urumqi,Xi′an,Lanzhou and Yinchuan municipalities between 2012 and 2017.Exposures to the heavy metals were estimated based on calculations of average daily dose(ADD)and life time average daily dose(LADD).Health risk assessment models were used to evaluate health risks of exposures to heavy metals in PM2.5 among different populations in the four cities.Results There were regional differences in the concentrations of the heavy metals,with the highest concentration of zinc(Zn)among the 7 heavy metal elements for the four cities.Both the annual mean values of arsenic(As)and hexavalent chromium Cr(VI)were higher than the reference limits for all the four cities and the value of cadmium(Cd)was higher than the reference limit only for Urumqi city.In terms of the four cities as a whole,the main contributor of non-carcinogenic risk was lead(Pb)among the heavy metals but its hazard risk(HR)was less than one with the highest HR for Xi′an city;while the contributor of carcinogenic risk was As.The values of lifetime cancer risk(LCR)associated with the exposure to As and Cr(VI)in PM_(2.5)were close to 10^(-4)for the residents in Urumqi city but the LCR values associated to the As and Cr(VI)exposure were both greater than 10^(-4)in Xi′an city;also for the residents of the two cities,the integrated lifetime cancer risk(ILCR)attributed to the exposures to the heavy metals exceeded the threshold level,with a higher LICR for the residents in Xi′an city.Conclusion There were health risks related to exposures to heavy metals in PM_(2.5)for the four metropolitan cities in Northwest China;among the four cities,both the non-carcinogenic and carcinogenic risk due to the exposure to the heavy metals were the highest in Xi′an city,followed by those in Urumqi city,and the risks were within acceptable range in Lanzhou and Yinchuan city.