| To reveal the effect of total organic carbon(TOC)and leaching amount on the vertical migration of polycyclic aromatic hydrocarbon(PAHs)and PAHs diagnostic ratios,the indoors column leaching experiments of PAHs vertical migration were carried out.Soil samples were collected from three soil profiles including Mentougou district,Fangshan district and Haidian district according to the TOC of soil.Twelve groups of soil column experiments have been conducted according to variables including TOC,leaching amount and the depth of column.Sixteen priority PAHs were added into topsoil as the high-polluted soil samples.Experiments were leached intermittently by deionized water for 30?90 days.The qualitative and quantitative analysis of PAHs in soil and leachates have been carried out and the vertical migration characteristics of PAHs were studied.The results show that:(1)Multiple linear regression analysis of PAHs content and physicochemical properties of natural soil profiles indicate that physicochemical properties of soil including TOC,clay content and p H are all influencing factors of the vertical distribution characteristics of PAHs in soil profiles,and TOC is the main factor.(2)PAHs with different rings migrate vertically in various degrees after leaching,and the differences of migration concentration of PAHs with different rings are related to their physicochemical properties,the higher the water solubility of PAHs molecules are,the lower the octanol-water partition coefficients(Kow),and the easier it is to migrate vertically with leaching.The decreasing order of vertical migration ability is low-ring PAHs,mid-ring PAHs,high-ring PAHs.Although TOC of soil is the main influencing factor for the migration concentration of PAHs in soil profile,the original concentration of PAHs in soil becomes the main factor when the original concentration of PAHs differs greatly among several columns.(3)The content of PAHs leaching from high-polluted soil is much higher than that from natural soil,which indicates that PAHs added into topsoil migrate vertically and are detected in the leachate.It is further proved that the short-term aging PAHs in the surface soil can quickly enter the deep soil through leaching and elute with the leachate,and it thus poses potential hazard to deep soil and shallow groundwater.And TOC of soil affects the migration concentration of PAHs as well as migration rate.The low-ring PAHs such as naphthalene,phenanthrene,anthracene and anthracene are detected at a higher level in leachate from various soil columns,and the concentration of mid-ring and high-ring PAHs are lower.(4)There is a significant nonlinear correlation between the cumulative concentration of PAHs in leachate from various columns and L/S.The fitting equation is:y=(6~3+(7~2+(8+(9,the correlation coefficient R~2 are greater than 95%,which indicates that the correlation is high.And the analysis of the curve model shows that the continuous leaching behavior of PAHs in soil has potential pollution risks for deep soil and shallow groundwater.(5)The leaching caused a large change in the distribution characteristics of PAHs source apportionment in the high-polluted column.With the increase of leaching amount,the low-ring PAHs are more prone to migrate vertically,resulting in change of PAHs pollution source indicated by the diagnostic ratio LMW/HMW.Under the premise that the octanol-water partition coefficient is similar,PAHs molecules with high water solubility are more likely to migrate vertically,which changes the diagnostic ratio of isomer.For example,the pollution source of PAHs identified by the diagnostic ratio Icd P/(Icd P+Bghi P)changes after leaching.Therefore,the impact of leaching should be considered when applying these diagnostic ratios. |
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