PRA在焦化厂污染土壤修复目标值制定中的应用

以某焦化污染场地为例,采用PRA(概率风险评价)方法研究了17个人体暴露参数和5个土壤理化性质参数的不确定性对土壤中8种污染物修复目标值的影响.结果表明:PRA与DRA修复目标值的比值仅深层Nap为0.9,其余为1.11~2.49,因此,采用传统的DRA(确定性风险评价)方法制定的修复目标值容易偏保守;将土壤中污染物含量降低到PRA修复目标值所产生的暴露风险均在可接受的范围内,但表层土壤Ben对人体健康产生危害的可能性最大;参数敏感性分析的结果表明成人暴露周期(EDa,贡献率为35%~59.8%)和儿童暴露周期(EDc,6.2%~20.2%)对各污染物修复目标值不确定性的影响均较大,此外,土壤理化性质参数,如土壤有机碳含量(foc)、土壤孔隙中空气体积比(θair,vad)和土壤孔隙中水体积比(θwater,vad)对易挥发的Ben和Nap影响较大,儿童每日土壤摄入量(IRs-c)对不易挥发的BaA~DBA影响较大.

Application of PRA in deriving soil cleanup level for a coking plant site

A Probabilistic risk assessment (PRA) was used to characterize variability and uncertainty of 17 parameters related to human exposure and 5 related to soil physicochemical properties in deriving the soil cleanup levels of 8 pollutants in a coking plant. Results showed that the ratios of PRA clean-up level to DRA clean-up level were 1.11~2.49, except for Nap in subsoil (0.9), therefore, the cleanup levels derived by using deterministic risk assessment (DRA) method were in general more conservative than these by using PRA in this case. If contaminants in soil were reduced to the PRA clean-up levels, all the exposure risks would be acceptable but at different levels, and Ben in topsoil was more likely to cause harm to human health than others. The sensitivity analysis revealed that adult exposure duration (EDa) and child exposure duration (EDc) both contributed most to the uncertainty (sensitive ratio: 35%~59.8% for EDa and 6.2%~20.2% for EDc) in the derivation of all the clean-up levels. Soil physic-chemical parameters, such as soil organic carbon content (foc), volumetric air content in soil (θair,vad) and volumetric water content in soil (θwater,vad), were more sensitive to volatile Ben and Nap and less to semi-volatile BaA~DBA. Contrastingly child soil ingestion rate (Irs-c) were more sensitive to BaA~DBA and less to Ben and Nap.