摘要
在某场地苯重点污染区布置10个钻孔,按规范采集检测了63对土壤-土壤气样品,基于土壤和土壤气VOCs浓度分别刻画了场地污染并评估了风险.结果显示,土壤采样和土壤气采样两种方法揭露的污染垂向分布特征基本一致,10个钻孔中采集的土壤气样品均存在一定程度超标,超过土壤气筛选值1.242mg/m^(3)的样品比例为35%,最大超标1000倍,但仅3个钻孔中采集的土壤样品存在超标,超过土壤筛选值1mg/kg的样品比例为5%,最大超标30倍.可见,仅检测土壤样品可能低估场地中VOCs的污染范围和程度,在以砂土为主的场地尤为明显.采用线性分配模型基于土壤中苯检出浓度预测的健康风险较基于实测土壤气中苯浓度预测的风险总体高约1个数量级,因为“老化”、“锁定”等环境行为导致实际污染场地中VOCs在土壤固-液-气间的分配并不完全遵循瞬间平衡分配原理,线性平衡分配模型预测的土壤气浓度显著高于实测值.此外,不考虑苯系物这类易生物降解的VOCs在传输过程中的生物降解过程可导致场地实际健康风险被高估至少2个数量级,评估结论会发生本质的变化.因此,我国应尽快启动基于土壤气的VOCs场地调查与风险评估技术方法的系统研究及相关标准规范的制定,为场地环境管理提供科学支撑.
Contamination characterization and vapor intrusion risk evaluation based on volatile organic compounds(VOCs)in bulk soil were recommended in the technical guidelines of China.However,these guidelines are found to be full of uncertainties in practical use.To evaluate its effectiveness,ten boreholes were drilled within an area contaminated by benzene in a decommissioned site,and 63 paired soil and soil gas samples were collected and analyzed following the technical guidelines.The results revealed that benzene profiles in the soil were similar,as revealed by both the soil and soil gas analyses.The benzene content in 35%of soil gas samples was above the screening level of 1.242mg/m^(3),and it was distributed in all the ten boreholes.The maximum concentration was nearly 1000 times the screening value.However,in only 5%of soil samples,benzene content was above the soil screening value of 1mg/kg,and the maximum concentration was about 30 times the screening value.Therefore,it can be concluded that analyzing the bulk soil may underestimate the VOC contamination in sites,especially for sites composed of sandy formations.The risk quantified based on soil contents using the linear partition equation was about one order of magnitude higher than that estimated based on measured soil gas concentration.The reason is that the partition of VOCs among soil solid,water,and vapor phases does not follow the linear equilibrium partition exactly due to the aging and sequestration of contaminants by organic matter in the soil.The vapor concentration is highly overestimated using the linear equilibrium equation.Additionally,risk can be overestimated by over two orders of magnitude without considering biodegradation throughout the intrusion process for VOCs(e.g.,BTEX)that can be degraded.The results may be entirely different.Therefore,systematic research on VOC contamination and risk characterization,as well as relevant technical guidelines based on soil gas,is suggested to be initiated.
作者
郝辰宇
钟茂生
姜林
李吉鸿
马琳
汪洋
HAO Chen-yu;ZHONG Mao-sheng;JIANG Lin;LI Ji-hong;MA Lin;WANG Yang(Beijing Key Laboratory for Risk Modeling and Remediation of Contaminated Sites,National Engineering Research Centre of Urban Environmental Pollution Control,Beijing Municipal Research Institute of Eco-Environmental Protection,Beijing 100037,China)
出处
《中国环境科学》
EI
CAS
CSCD
北大核心
2023年第11期5700-5708,共9页
China Environmental Science
基金
国家自然科学基金资助项目(42177404)。
关键词
土壤气
挥发性有机物
污染刻画
蒸气入侵风险
soil gas
volatile organic compounds(VOCs)
contamination characterization
vapor intrusion risk
