兰州市大气PM2．5中重金属的污染特征及健康风险评价

Pollution characteristics and health risk assessment of heavy metals in PM2.5 in Lanzhou

目的了解兰州市两个不同功能区大气PM2.5中重金属元素的污染水平及其对人群造成的健康风险.方法根据兰州市空气污染的区域特征和工业企业分布特征,以兰州市城关区和西固区为采样点.于2015年1月至2016年12月对两区进行PM2.5逐月连续采样,采用电感耦合等离子体质谱法测定PM2.5中12种金属元素Sb、Al、As、Be、Cd、Cr、Hg、Pb、Mn、Ni、Se和Tl的浓度,并应用富集因子、地累积指数法分析其污染特征,采用美国环境保护署（EPA）推荐的健康风险评估模型评价其所致健康风险,以非致癌风险商（HQ）评价单种污染物的非致癌风险,HQ〈1非致癌风险较低,HQ〉1.0为存在非致癌健康风险;并评价单种污染物的致癌健康风险,10^-6～10^-4为可接受风险水平.结果采样期间兰州市城关区和西固区PM2.5浓度中位数分别为83.0、77.0μg/m^3.检测到的7种金属元素（Al、Pb、Mn、As、Sb/Cd、Tl）中,除Al、Mn元素主要受自然因素影响外,其余5种元素均为典型的人为污染元素,以Cd元素在冬季的污染程度最强（地累积指数〉5）.非致癌风险均以Mn元素最高（HQ〉1）,且对儿童造成的健康风险最大,城关区HQ高达2.44,西固区HQ亦达1.79.Pb、As、Sb、Cd对各类人群的非致癌风险商HQ均小于1,健康风险较小;As、Cd元素的致癌风险范围为6.33×10^-6～6.46×10^-5,介于可接受风险水平（10^-6～10^-4）之间,具有潜在的致癌风险.结论兰州市大气PM2.5及其中重金属的污染形势依然严峻,多种重金属联合作用对儿童造成的非致癌健康风险应引起高度重视,重金属As、Cd元素的致癌风险虽介于可接受风险水平10^-6～10^-4之间,但对其造成的可能致癌风险仍不可忽视.

Objective To understand the pollution characteristics and assess the pollution health risks of heavy metals in atmospheric PM2.5 in Lanzhou. Methods According to the regional characteristics of air pollution and industrial distribution characteristics in Lanzhou, atmospheric PM2.5 was sampled monthly in Chengguan and Xigu Districts from January, 2015 to December, 2016. Detected the concentration of PM2.5 and 12 kinds of elements （Sb, Al, As, Be, Cd, Cr, Hg, Pb, Mn, Ni, Se and Tl） by weighing method and inductively coupled plasma mass spectrometry. Enrichment factor and geo-accumulation index were used to describe the pollution characteristics, while health risk assessment was conducted using the recommended United States Environmental Protection Agency（USA EPA）model. The health risks of non-carcinogens were evaluated by non-cancer hazard quotient （HQ）, the non-carcinogenic risk was considered to be negligible when HQ〈1, HQ〉1 meant a health risk. With a single contaminant cancer Risk value to evaluate the health risks of carcinogens, when the Risk value between 10^-6 to10^-4 as an acceptable level. Results The daily average concentrations of PM2.5 was 83.0 μg/m^3, 77.0 μg/m^3 in Chengguan and Xigu Districts, respectively, during the sampling periods, and the concentration of PM2.5 in winter/spring was higher than summer/fall in both districts. The concentration of Al in PM2.5 was the highest and other elements in descending order：Pb, Mn, As, Sb/Cd, Tl in both districts. Enrichment factor results showed that Al and Mn were mainly affected by natural factors, the rest of five elements were all typical man-made pollution elements and according to geo-accumulation index pollution level of Cd was the strongest in the winter. The results of health risk assessment showed that Mn had the highest non-cancer risks （HQ〉1） and affected the health of the children seriously. HQ reached up to 2.44 and 1.79 in Chengguan and Xigu Districts, respectively. Pb, As, Sb, Cd had slight health impact （HQ〈1）, could be negligible. The cancer risks range of As, Cr were 6.33×10^-6 to 6.46×10^-5 between the acceptable level of risk （10^-6 to 10^-4）, which indicated that As and Cd had potential cancer-risks. Conclusions The pollution level of atmospheric PM2.5 and the heavy metals in it was still grim;the non-cancer risks caused by multiple metals on children deserved attention. Although the cancer risks of As and Cd were between the acceptable level of risk, the potential cancer risk still shall not be ignored.