Effects of aging on the mobility of PAHs in soils

The goal of this study is to generate scientific knowledge and data that may rake into account the major mechanisms of aging in the predictive models of of organic contaminant behavior in soils. The effects of aging on the mobility of PAHs have been investigated using laboratory batch and column assays. Naphthalene and phenanthrene have been used as model contaminants because they are the most soluble PAHs. Experiments were conducted with four soil matrices: a sand, a clay, and two soils with different organic contents. Aging was conducted in water saturated and non-saturated conditions, under different conditions of temperature (constant temperature (20 degrees C) or freeze/thaw cycles). Experimental results of the batch assays showed a reduction of the pollutant mobility with increasing aging times. Freeze/thaw cycles were found to reduce this effect significantly and increase the extractability of naphthalene. The observed effects of aging may be related to possible evolutions of pollutant/sorbent interactions, mechanical alterations of the soil micro-aggregates, and slow diffusion of naphthalene or phenanthrene in micro-pores.