ABSTRACT

Polycyclic aromatic hydrocarbons (PAHs) may drive remediation at impacted soil or sediment sites. Current equations for calculating the PAH concentrations in soil that are protective of underlying groundwater (i.e., soil screening levels, or SSLs) generally assume a three-phase partitioning model, wherein PAHs partition among the soil matrix, porewater, and pore air. This simplified model does not consider the oil phase, and therefore overestimates the dissolved PAH concentration, and consequently, overpredicts the mobility and toxicity of PAHs to receptors especially when the source of PAHs is oil. This results in unnecessarily stringent cleanup goals and adds to the cost of treatment and management of impacted soils.

Complicating factors leading to the overestimation of dissolved PAH are that oil weathering (1) decreases to the effective solubility of the lower molecular weight PAHs, and (2) the presence of the oil itself increases PAH retention in the oil phase, thereby reducing aqueous/dissolved PAH concentrations. This is particularly important when oil is both the source and the factor controlling its solubility. In this paper, we have incorporated additional partitioning factors into existing SSL equations to capture the impact of oil weathering on PAH partitioning: The oil-water partitioning coefficient (K_OIL) for crude oils was measured at different stages of weathering using a passive sampling device (PSD). Results confirm that current methods for deriving SSLs are highly conservative and that the aqueous concentrations and mobility of PAHs are lower in soils and sediments that contain weathered oils. Thus, the mobility of PAHs in historically impacted soils is much lower than what is assumed when calculating SSLs for soil-leaching-to-groundwater scenarios.

摘要

多环芳烃 (PAHs) 可能会推动受影响土壤或沉积物场地的修复。目前用于计算土壤中保护下层地下水的 PAH 浓度（即土壤筛选水平或 SSLs）的方程通常假设三相分配模型，其中 PAHs 在土壤基质、孔隙水和孔隙空气之间分配。这个简化的模型没有考虑油相，因此高估了溶解的 PAH 浓度，因此高估了 PAHs 对受体的流动性和毒性，特别是当 PAHs 的来源是油时。这导致了不必要的严格清理目标，并增加了受影响土壤的处理和管理成本。

导致溶解的 PAH 被高估的复杂因素是油的风化 (1) 降低了较低分子量 PAH 的有效溶解度，以及 (2) 油本身的存在增加了 PAH 在油相中的保留，从而降低了水/溶解的 PAH 浓度。当油既是来源又是控制其溶解度的因素时，这一点尤其重要。在本文中，我们在现有的 SSL 方程中加入了额外的分配因子，以捕捉油风化对 PAH 分配的影响：油水分配系数 ( K _OIL) 使用被动采样装置 (PSD) 在不同风化阶段测量原油。结果证实，目前获得 SSLs 的方法非常保守，并且 PAHs 的水浓度和流动性在含有风化油的土壤和沉积物中较低。因此，PAHs 在受历史影响的土壤中的迁移率远低于计算土壤浸出至地下水情景的 SSLs 时的假设值。