Effect of freeze–thawing cycles on soil aging behavior of individually spiked phenanthrene and pyrene at different concentrations

This work was initiated to study the concentration effects on phenanthrene and pyrene extraction during process of aging in phaeozem and burozem with or without freeze–thawing cycles. 1, 10, and 100 μg g− 1 phenanthrene and pyrene contaminated soils were extracted by 10,000 mg L− 1 surfactant SDBS at various times. The extraction amount decreased with increasing contact time. Aging process could be divided into two stages: an initially rapid and then a slow sorption period. The amount extraction of 1 μg g− 1 pyrene in phaeozem was higher at the initial sorption stage. The time for 100 μg g− 1 phenanthrene and pyrene extraction efficiency to reach equilibrium in both soils were shorter than 1 and 10 μg g− 1. Changes in extraction efficiency rate caused by slow sorption were affected by contact time, physicochemical properties of soils and chemicals and the applied concentration of chemicals. For 1 and 10 μg g− 1 phenanthrene and pyrene contaminated soils, freeze–thawing cycle increased the extraction efficiency at the initial 1st and 8th days. The extraction efficiency with no freeze–thawing cycle was higher than that with freeze–thawing cycles at 30 and 120 days. A conceptual model was proposed to account for this process.

► Concentration effect on PAHs' extraction was studied.
► Changes in extraction efficiency rate caused by slow sorption were analyzed.
► Conceptual model of the interactions between SOM and chemicals was proposed.
► A new way on studying the aging behavior of HOCs was suggested.