我国农田土壤中挥发性有机物的残留特征及释放规律

A wide variety of volatile organic compounds (VOCs) could be ubiquitously detected due to their large quantity of emissions and high atmospheric migration, which may continuously pose threat to human health. The definition of VOCs by US EPA (ASTM D3960-98) is any organic compounds that can be photo-reaction in atmosphere. Soils, which are the sources and sinks of VOCs, play critical roles in the emissions of VOCs. Therefore, it is necessary to study the residual characteristics of VOCs in agricultural soils and their emissions. In this study, headspace-GC-MS (HS-GC-MS) and canister sampling-cold trap preconcentrator-GC-MS (CS-CTP-GC-MS) are employed to establish the analytical methods for VOCs in soils and the air, respectively. Metal-organic frameworks (MOFs) were also synthesized and prepared for determination of VOCs in the air. We involve three ways, including nation-wide sampling campaign, mathematics model and field simulation experiment, for this study. We aimed to describe the horizontal and vertical spatial distribution of VOCs in agricultural soils across China and establish the residue and emission inventories of them. The factors influencing the residues and emissions of VOCs in soils are explored. Then the emission characteristics are discussed. In addition, compound-specific isotope analysis (CSIA) is used to quantitative and qualitative identify the sources of VOCs in agricultural soils. Finally, the carcinogenic and non-carcinogenic risks of soil VOCs to human health are estimated. The results from this study will provide basic scientific data for better understanding the environmental behaviors, fate and risks of VOCs, as well as for their contamination management and risk avoidance in Chinese agricultural soils.

挥发性有机物（VOCs）具有种类多、排放量大、迁移性强等特点，是大气污染的主要成分之一。土壤作为VOCs重要的源和汇，其释放行为对大气环境质量起着一定作用。因此，探索土壤VOCs的残留特征和释放规律是十分必要的。本项目拟以多种不同类别的VOCs为研究对象，建立利用顶空-气质联用、苏码罐采样-冷阱富集-气质联用和新型检测材料（MOFs）快速检测等分别监测土壤和空气中VOCs的方法，通过大尺度野外样品采集、数字模型模拟和大田模拟实验三种手段相结合的方式，揭示我国农田土壤VOCs水平和垂直空间分布特征，建立全国范围土壤VOCs的残留清单和释放清单，识别影响我国农田土壤VOCs残留和释放的关键环境因素，探索其释放和扩散规律，并利用单体稳定碳同位素方法定性和定量识别VOCs的来源；最后综合评估我国农田土壤典型VOCs潜在的人群暴露风险。研究成果将为土壤VOCs的管控和风险规避提供科学依据。

挥发性有机物（Volatile Organic Compounds，VOCs）通常指沸点在50-260 °C之间，室温下饱和蒸汽压大于133.132 kpa的一类有机污染物。土壤VOCs污染往往具有隐蔽性，挥发性、累积性、多样性和强毒害性等特征。因此，初步建立我国农田土壤典型VOCs的残留清单，全面评价该水平下可能产生的生态健康风险具有紧迫的现实意义。本项目采样点进行了全国范围内农田土壤样品，分析测定了我国农田土壤中典型VOCs（包括BTEXS和VHCs）的残留浓度，明确其空间分布特征，进一步探究其可能来源及影响因素，并在此基础上利用健康风险评价模型评估了暴露于农田土壤BTEXS和VHCs所产生的健康风险。主要成果如下：. （1）BTEXS污染在两批土壤样品中均被普遍检出。2013年及2016年农田表层土壤中BTEXS总残留浓度的最高值分别为375和569 ng/g。在几种BTEXS中，甲苯为主要检出物质，其次为苯；超过半数的土壤样品中，甲苯为含量最高的BTEXS污染物。我国东北部为甲苯分布的“热点”地区；利用健康风险评价模型评估我国农田土壤中BTEXS通过土壤摄入，皮肤接触和长期吸入三种途径暴露后对人体产生的非致癌风险和致癌风险。各采样点非致癌风险的HI值均低于1。此外，苯对成人和儿童的平均致癌风险基本低于10-6，表明其对成人和儿童产生的致癌风险处于非常低的水平。. （2）被调查的18种典型VHCs中，共有13种VHCs在本次土壤样品中检出。检出率最高的五种物质依次为三氯甲烷（CF）（99.11％），1,2-二氯乙烷（1,2-DCA）（71.43％），二氯甲烷（DCM）（65.18％），氯苯（CB）（37.50％）和1,4-二氯苯（1,4-DCB）（38.39％）；五种主要检出物质中，DCM，CF和1,2-DCA的分布情况相似，以华北和西南地区的污染最为严重。中国东北部是1,4-DCB分布的“热点”地区，同时东北地区土壤中的CB含量也很高；商业溶剂挥发释放及工业生产泄露是土壤卤代烷烃的主要来源。. 典型VHCs不会对当地居民产生非致癌性风险。VHCs的五种主要检出的化合物中，CF对成人和儿童产生的非致癌性风险最大。本研究结果可为我们理解中国农田土壤中VOCs污染的来源及可能产生的后果提供数据支持，以期更有效地控制土壤污染