Sorption And Aging Of Polycyclic Aromatic Hydrocarbon (Pyrene) In Paddy Soils And Their Particle-size Fractions

Recently, more and more attentions are paid on the behaviors and fates of polycyclic aromatic hydrocarbons (PAHs) because of their potential hazard and risks to environment and humans. Sorption is a crucial process for PAHs bioavailability, volatilization and transport in soil. Aging is considered as a process of slow sorption, and has impact on the extractability and bioavailability of PAHs in soils. In this dissertation, we investigated the sorption and aging of pyrene in two types of paddy soils, Wushantu and Huangnitu (Gleyic Stagnic Anthrosols and Ferric accumulic Stagnic Anthrosols respectively) collected from Taihu Plain and their particle-size fractions. The results showed as follow:1. The sorption isotherms of pyrene on the paddy bulk soils and their particle-size fractions can be described well with Freundlich Equation, q = K_dC_e~N, and the N valueswere 0.404-0.698. For Wushantu and its particle-size fractions, the K_d values decreased as follow, clay(405)>coarse sand(218)>bulk soil(172)>silt(148)>fine sand(137), while in the Huangnitu and its particle-size fractions, the Kd values decreased in the order bulk soil (781)>coarse sand (352)>clay(282)>fine sand(221)>silt(205). Thus coarse sand and clay had larger capacity for pyrene sorption.2. When K_d values were normalized by soil carbon contents, they were shifted to K_oc. If the logKoc value of clay fraction was excluded, there were no difference between of logK_oc values (4.03-4.05) of Wushantu bulk soil and other particle-size fractions, it is similar for the logKoc values of Huangnitu particle-size fractions (4.13-4.17) except for that of bulk soil (4.65). These proved that SOM content was a key factor for pyrene sorption in paddy soils and their particle-size fractions. In general, the logK_oc values of Huangnitu bulk soil and its particle-size fractions were larger than those of Wushantu bulk soil and its particle-size fractions. It showed that the former samples had larger capacity for pyrene sorption than the latter samples, and suggested that the properties of SOM in Huangnitudiffer to that in Wushantu.3. The K_d values were significantly correlated with dithionite-extractable Fe, indicating the effects of surface characteristics on the sorption of pyrene in paddy soils and their particle-size fractions. In Wushantu bulk soil and its particle-size fractions there was a positive correlation between K_d values and CEC content, while no relationship between them was found in Huangnitu.4. In a cosolved solution of pyrene and phenanthrene, the sorption isotherms of phenanthrene also well fit the Freundlich Equition, but the N values were more closer to 1. This indicated that pyrene suppressed phenanthrene sorption and increased the linearity of its isotherms. While higher phenanthrene concentration can promot pyrene sorption on Wushantu bulk soil and its coarse sand, fine sand, and silt fractions. But there was no change of pyrene sorption on clay size with different concentration phenanthrene.5. The extractability (with dichloromethane, DCM) and earthworm uptake of pyrene decreased with the compound persistent in paddy buld soils and their particle-size fractions. In all samples, the aging process was largely completed within 120 days based on the changes of extractability. Aging can significantly reduce the extractability and bioavailability of pyrene (P<0.05).Saturated water content and high pyrene concentration can weaken the effect of aging. Soil particle-size fraction may be another important factor affecting aging of pyrene in paddy soils.There was a significant correlation between pyrene extractability (DCM) and earthworm uptake. The results suggested that it was feasible to predict bioavailability of persistent organic compounds in soil by chemical procedures.