Relationships between aging of PAHs and soil properties.

Sequestration and diffusion of three polycyclic aromatic hydrocarbons (PAHs) in seven Chinese soils were investigated for up to 200 days in sterile soil microcosms as functions of soil property and aging time. The aging of the PAHs, assessed using a mild extractant that removes primarily the labile fraction, showed a biphasic behavior. The rapid diffusion from labile to nonlabile domains was mainly dependent upon the distribution of meso- and micropore fraction and total organic carbon content. Meanwhile, the slow diffusion was found to decrease with the increase of the content of soil organic carbon, particularly of hard organic carbon (p < 0.01) and the meso- and micropore fraction, as well as with the increasing molecular size of PAHs. This work offers evidence that analyses of organic carbon fractionation and porosity are important to adequately assess the mechanistic basis of sequestration and diffusion of organic contaminants in soils.