Effects of aging and freeze-thawing on extractability of pyrene in soil

The effects of soil freezing and thawing on the extractability by dichloromethane of pyrene from two Chinese soils are investigated. The soils were collected from the Northeast region of China where heavy pollution of soils by Polycyclic Aromatic Hydrocarbons (PAH) is common. Two soils were considered: a burozem obtained from the Shenfu irrigated region in Liaoning province and a phaeozem collected from the Hailun area in Haerbin province. The soils were collected from areas free from PAH pollution. Pyrene was aged in sterilized soil, and autoclaved deionized water was then added to adjust the soil to different moisture levels. The combined dichloromethane extractions of pyrene in soils at various periods showed that the quantity of pyrene extracted with dichloromethane could be divided into two stages: the initially rapid period and a longer, slower period. The frequency of freeze-thawing cycles had different and contradictory effects on pyrene extractability between the two soil types. Soil moisture also was found to have different and opposite effects on pyrene extractability. Freeze-thawing cycles had great influence on pyrene extractability both in aged and unaged soils. The changes in unaged soil were more significant than those in 1-year aged soil and attributed to changes in the soil organic matter. Our research shows that the effect of freezing and thawing on pyrene extraction is complicated due to the differences in physical and chemical properties of soils as well as the aging process.