XAD-2树脂表征焦化厂土壤中高环PAHs的生物可给性

利用Amberlite XAD-2树脂辅助解吸技术表征某焦化厂土样中高环PAHs的解吸特征及其生物可给性,分析风险评估过程中考虑污染物生物可给性的可行性；采用傅里叶红外光谱法测试解吸前、后土样的红外光谱特征,判断不同土壤有机官能团对PAHs的吸附强弱. 结果表明:土样中PAHs前30 d的解吸速率明显大于后60 d(前者的解吸速率比后者高2～3个数量级),60 d后污染物解吸基本已达到平衡,整个过程符合两阶段解吸模型. 渗漏污染途径下土样中高环PAHs的生物可给性为0.18～0.47,低于大气沉降污染途径下表层土样中对应PAHs的生物可给性(1.00),表明在开展场地健康风险评估过程中,应考虑具体场地土壤中PAHs的生物可给性,以在一定程度上降低评估结果的保守性. 解吸前、后土样红外光谱特征整体无明显变化,解吸过程不改变土壤主要有机官能团类型,但解吸后土壤中羟基和羧基的峰强明显减弱,吸附于羟基及羧基上的PAHs可能更易解吸. 

Assessing the Bioaccessibility of High Molecular Weight PAHs in Soils from a Coking Plant Using XAD-2 Assisted Desorption Method

Abstract:To determine the bioaccessible fraction of PAHs concentration, a desorption experiment assisted by XAD-2 resin was employed to characterize the desorption process and bioaccessibility of high molecular weight PAHs (HMW PAHs) in the soils of a coke and chemical plant. In order to evaluate the sorption of PAHs with different functional groups in the soils, FTIR technique was used to characterize the infrared spectrogram of the soil samples before and after the desorption experiments. The desorption leveled off after 60 days, and the rates in the first 30 days (fast desorption phase) were two to three orders of magnitude higher than the ones in the last 60 days (slow desorption phase), which could be regressed by dual-phase model. Bioaccessibilities of the corresponding HMW PAHs were 0.18-0.47 in the soil samples contaminated through leakage of PAHs-containing liquid, while they were 1.00 in the surface soil samples contaminated via precipitation. This suggests that it may be conservative to simply assume bioaccessibility in all soil is 100%. The difference between infrared spectrograms of the samples before and after desorption was negligible, indicating the main function groups in soil organic matters was not changed during the experiment. However, the peaks of hydroxyl and carboxyl in the spectrograms shrunk, implying that PAHs adsorbed on these function groups might be more bioaccessible. The results suggest that bioaccessibility should be considered in a specific site to reduce the conservativeness of health risk assessment.