The Bioegradation Of Polycyclic Aromatic Hydrocarbons In Soil And Its Effect On The Validity Of Pahs Source Analysis Parameters

To reveal the differences of unti-microbial degradation ability of Polycyclic aromatic hydrocarbons(PAHs)composition in soils and to explore the variation characteristics of PAHs compositions and the influence of source apportionment parameters in the process of microbial degradation,four strains,including Pseudomonas,Achromobacter,Empedobacter brevis and microbacterium,were isolated from contaminated soil sampled.The biodegradation experiments were conducted from 15 to 150 d(15,20,30,40,50,60,90,120 and 150 d respectively),and three groups of PAHs monomer(each group included two compounds),16 PAHs and crude oil were used as substrates.The results of biodegradation experiments indicate that:(1)For the single medium of PAH monomer,the highest total loss rate of phenanthrene and anthracene could reach up to 98.50% and 59.04% separately during the 150 d degradation period,the maximum biodegradation ratio of them are 29.39% and 68.43% which indicates that the blank loss has a great influence on the removal of phenanthrene.The relative degradation rates of four-ring-PAHs(except chrysene)increased with the degradation time,the highest degradation rate of them(fluoranthene,pyrene,benzo [a] anthracene)are up to 35.59%,35.25% and 32.29% respectively.The variation of total loss rate of chrysene is not obvious and its highest relative degradation rate is up to 16.15%.(2)The degradation of 16 PAHs is more complicated: the highest total loss rate of three-ring and four-ring PAHs(including phenanthrene,anthracene,fluoranthene,pyrene,benzo [a] anthracene,chrysene)could reach up to 97.78%,92.73%,91.36%,90.48%,50.64% and 39.39%,separately;The loss rate of other PAHs with high rings are about 0.56%~70.32%,among them the the highest loss rates are benzo[b]fluoranthene and indene [1,2,3-c,d] pyrene which up to 69.97% and 70.32%,both of them have been on an upward trend.(3)In the medium of crude oil,the content of PAHs in crude oil decreased from 0.5 g to 0.21 g with the degradation time,which indicated that there is a good effection on the degradation of crude oil,but there is a significant difference in the loss rate of PAHs with different number of rings.The relative biodegradation rate of three-ring and four-ring PAHs(including phenanthrene,pyrene,fluoranthene,pyrene,pyrene)increased and then decreased with the degradation time,the reason may be that the degradation of the alkyl-PAHs or LMW PAHs produced by the degradation of HMW PAHs.(4)The biodegradation has a certain effect on PAHs source apportionment parameters in different degradation conditions.As observed for the combined medium of 16 PAHs,An/(An+Ph)incresed with the degradation time,while parameters including Fl/(Fl+Py),BaA/(BaA+Chr)and LMW/HMW showed an degrade trend with the degradation time;In the oil crude medium,parameters of LMW/HMW decreased gradually,while parameters including An/(An+Ph),Fl/(Fl+Py),BaA/(BaA+Chr),IcP/(IcP+BgP)changed complicated in 150-day degradation period.However,most of the source apportionment parameters in the 150 d degradation period have been significantly affected,so that we need to be careful with these parameters for source analysis.(5)In the medium of crude oil,most alkyl-PAHs parameters changed with time,among them,C0/(C0+C1)ratio of phenanthrene,C0/(C0+C1)ratio of fluorine and pyrene changesd obviously during the degradation period of 150 days,the value of MP/P and MPI1 have little changes during the whole biodegradation period and the value of MPI1 after degradation always higher than that in undegraded crude oil.