城市高架桥降雨径流多环芳烃(PAHs)污染特征及其生态风险评价

The Characteristics of PAHs pollution and relative ecological risk assessment in viaduct runoff

以上海市高架桥降雨径流作为研究对象，分析了4场高架路面降雨径流溶解相、颗粒相16种PAHs的质量浓度和场次降雨径流平均浓度（Event Mean Concentration）。探讨了城市高架降雨径流中PAHs质量浓度特征、动态变化过程和污染状况。通过对无量纲累积径流量和无量纲累积污染物负荷曲线M（V）进行幂函数拟合，对4场降雨径流不同环数和总PAHs冲刷强度进行了定量表征。以水样中8种PAHs的监测质量浓度及其对3至40种水生生物的LC50为基础数据，采用推广风险系数法对径流水体PAHs进行了生态风险评价。结果表明：地表径流中溶解态PAHs的质量浓度为27.9~979.4 ng·L-1，主要以3环和4环组分为主；颗粒态PAHs中的质量浓度为1120.1~4892.6 ng·L-1，主要以4-6环的组分为主。径流样品中PAHs更容易吸附在颗粒物上，PAHs主要以颗粒相为主，且4-6环颗粒相PAHs所占比例更高，也显示了化石燃料不完全燃烧的特征。4场降雨径流以2013-05-26次降雨EMC值最大，PAHs污染水平最高。其中通过对BaP的EMC值计算，发现4场降雨径流中BaP的EMC值皆超过了国家的排放标准，应引起相关监测管理部门重视。4场降雨径流均表现不同程度的初始冲刷效应，雨强和径流量是影响初始冲刷的2个重要因素。初始冲刷散点拟合状况良好，定量表征发现2013-06-27次降雨初始冲刷强度最大。风险商表征说明，径流水体PAHs造成的生态风险较小，但部分单体PAH对水生生物的生态影响不容忽视。

In this paper, polycyclic aromatic hydrocarbons （PAHs） in four rainfall runoff samples were studied at two typical viaducts in Shanghai during the rainy season of 2013. Sixteen EPA PAHs in both dissolved and particle phases were analyzed in order to characterize the PAHs concentrations and dynamic variation between the two phases. The dimensionless cumulative runoff＆amp;nbsp;volume and mass curve M（V） were conducted in a method of fitting power function to quantitatively assessed the magnitude of first flush effect （FFE）. Based on the observed concentrations of the runoff samples and LC50 values of a number of aquatic organisms, the generalized risk factor approach was employed to address the ecological risk of 8 PAHs to aquatic ecosystem. The result indicated that the dissolved PAHs concentrations varied from 27.9 to 979.4 ng·L-1, mainly from 3 and 4 rings. Whereas, the concentrations in particle phase ranged from 1 120.1 to 4 892.6 ng·L-1, and 4 to 6 rings were the dominant compounds. As PAHs are mostly adsorbed on particles in runoff, the fact that particle-bound PAHs, especially for 4-6 rings PAHs, accounted for a larger proportion revealed incomplete combustion of fossil fuels as the main source of PAHs in runoff. According to the event mean concentration （EMC）, the PAHs pollution level was the highest in the rainfall event 2013-05-26. The EMC value of BaP was much higher than the applicable discharge standard of China, which should give rise to the enough attention by environmental monitoring centre. The occurrence of FFE was found in 4 rainfall events on different levels, and the FFE was largely dependent on rainfall intensity and runoff volume. The quantitative characterization of FFE showed the magnitude of the FFE in the rainfall event 2013-05-26 was the greatest. The hazard quotient indicated that although the overall ecological risk was low, it had posed threat to some aquatic organisms.