| In order to reveal distribution characteristics of PAHs in different types of soils,several PAHs species with different rings and 16 USEPA priority PAHs mixture were applied as additive pollutants in the study of the distribution characteristics of PAHs in paddy soil,cinnamon soil and Chao soil.The time gradient in partitioning experiments was set as 1d,7d,15d,30d,45d,60d,75d,90d and 105d.The results show that the physical and chemical properties of the three soils were significantly different from each other.Paddy soil with high water content is sandy loam soil;cinnamon soil with low water content is a little bit hard and belongs to loamy sand;Chao soil belongs to sand loam and silt loam with a soft texture.Among the three soils,the content of humin accounts for over 50% of organic matter,while the content of humic acid in paddy soil is higher than that in cinnamon soil and Chao soil.In addition,the aliphatic structures are relatively high in Chao soil,and more aromatic structures are detected in paddy soil and cinnamon soil.The total amount of PAHs detected in three soils is 5.74 ng·g-1,6.82 ng·g-1 and5.29 ng·g-1,respectively,which were much smaller than the addition amount.Therefore,the background value of PAHs in experimental soils has no obvious impact on the study conclusion.The partition equilibrium durations of different PAHs in the same soil are different,and that of each PAHs in different soils are different as well.For example,PAHs with median and high-ring reach equilibrium in 15d,while Phe in 30d in the paddy soil.As for the partition equilibrium durations of different compounds,such as 3-ring?Phe?and4-ring aromatics?BaA and Chry?,the orders are ranked as follows:paddy soil?cinnamon soil?Chao soil.However,for 5-ring PAHs?BaP?,the order is paddy soil>Chao soil>cinnamon soil.In addition,the value of lgKoc of specific PAHs is similar in three soils.Therefore,soil types have no obvious effect on the value of lgKoc.In the experiment with 16 PAHs mixture,the partition equilibrium durations of total PAHs concentration are sequenced as paddy soil>Chao soil>cinnamon soil.However,the proportion of PAHs with different rings is similar in total PAHs concentration during partition equilibrium period.In addition,the equilibrium durations of different PAHs monomers are significantly different from each other.For 3-ring aromatics,the change of partition equilibrium duration is not obvious;but the partition equilibrium durations of PAHs with median and high-ring are all 30 days,except for those of Flua in paddy soil and DBA in Chao soil which are 15 days.Additionally,the curves of lgKoc*of PAHs with the same ring vs.the time are almost the same.There are differences in both of the partition equilibrium duration of different PAHs in three soils and the equilibrium concentration between the trials of PAHs monomers and 16 PAHs mixture.In comparison with PAHs monomers trials,Phe reaches equilibrium after a longer partition time and has a higher equilibrium concentration at in the PAHs mixture trial.While the partition equilibrium duration of4-ring and 5-ring PAHs are almost the same in both cases.The concentrations of 4-ring PAHs in soils are sequenced as:paddy soil>Chao soil>cinnamon soil.The concentrations of BaP are the same at equilibrium.When the partition processes reach equilibrium,the values of lgKoc of PAHs monomers increase with molecular weight.Furthermore,when PAHs with different rings reach partition equilibrium in the same soil in two trials of PAHs addition,the adsorption capacity of PAHs has the same trend:5-ring>4-ring>3-ring. |
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