高速路沿线土壤多环芳烃赋存特征及生态风险

Distribution Characteristics and Ecological Risk of Polycyclic Aromatic Hydrocarbons in Surface Soil of the Expressways

文章以上海市5条典型高速公路的通行段及收费站土壤为研究对象,对比分析其表层土壤中15种多环芳烃含量、组成分布特征,并以毒性当量法和风险熵值法评价其生态风险。结果表明,高速公路沿线表层土壤中∑PAHs的含量为150~18160μg/kg,平均值为3529μg/kg,∑PAHs含量占PAHs总量的55.9%,占比相对较高。通行段土壤中∑PAHs的含量为150~1951μg/kg,平均值为590μg/kg;收费站土壤中∑PAHs的含量为421~18160μg/kg,平均值为6467μg/kg,收费站土壤中PAHs含量是通行段土壤的2.5~66.3倍,存在显著差异。高速公路沿线土壤中多环芳烃组成均以中高环为主,收费站土壤多环芳烃中环占比要高于通行段,其中荧蒽、苯并[a]蒽和芘单体占比明显更高,通行段土壤中茚并[123-cd]芘和苯并[ghi]苝占比较高。收费站土壤多环芳烃的生态风险高于通行段土壤,其中葛隆和临港2个收费站土壤中多环芳烃的总毒性当量分别为土壤风险筛选值的5.4倍和2.3倍,存在较大风险。从风险熵值来看,收费站土壤蒽、芘、苯并[a]蒽、苯并[b]荧蒽等4种单体超过最高允许风险标准值,存在较高风险需关注;通行段土壤PAHs生态风险主要为中等风险。综上,交通沿线土壤中PAHs呈现出明显的累积性,其赋存特征与通车时间、车流量及货客车占比有关,其中收费站附近机动车怠速运行工况以及相对不利的尾气扩散条件,导致其土壤多环芳烃呈现较高含量及生态风险水平,需进一步加强高速公路周边交通源产生的多环芳烃污染防控。

Five typical high-speed sections and toll stations of expressways in Shanghai were selected as research object,soil samples of which were collected.The content,and distribution characteristics of polycyclic aromatic hydrocarbons(PAHs)were analyzed,and the ecological risk was evaluated by toxicity equivalent(TEQ)and risk quotient(RQ).The results showed that the content of∑PAHs in expressway soil ranged from 150μg/kg to 18160μg/kg,with an average of 3529μg/kg.The content of∑PAHs accounted for 55.9%,which was a relatively high proportion.The content of∑PAHs in soil adjacent to high-speed sections were 150~1951μg/kg,with an average of 590μg/kg;the content of∑PAHs in soil adjacent to toll stations was 421~18160μg/kg,with an average of 6467μg/kg.The content in soil adjacent to toll stations was 2.5~66.3 times as high as high-speed sections,which were statistically different.PAHs in expressway soil were mainly composed of medium and high rings.The proportion of medium-ring PAHs in soil near toll stations was higher than high-speed sections,especially fluoranthene,benzo[a]anthracene and pyrene.On the contrary,Indeno[1,2,3-cd]pyrene and Benzo[g,h,i]perylene in soil of high-speed sections had more proportion than toll stations.Ecological risk assessment indicated that soil adjacent to toll stations was higher risk than high-speed sections,particular Gelong and Lingang stations in which soil TEQ of∑PAHs were 5.4 times and 2.3 times of the risk screening value for soil contamination of agricultural land,respectively.RQ evaluation showed that the RQof Anthracene,Pyrene,Benzo[a]anthracene,and Benzo[b]fluoranthene in soil of toll stations were higher than 1.0,indicating high risk needed to be paid attention;PAHs in high-speed sections had medium risk with RQ(more than 1.0)and RQ(less than 1.0).Distribution characteristics and ecological risk of PAHs in soil had accumulation effects,which related to road service hours,vehicle flow and vehicle type.The low-speed operation of vehicles and unfavorable diffusion conditions of exhaust gas near toll station caused high content of PAHs and high ecological risk.It was necessary to strengthen the prevention and control of PAHs pollution from traffic source.