Study On Degradation Properties And Mechanism Of Phenanthrene,Fluorene And Fluoranthene By White Rot Fungi

Polycyclic aromatic hydrocarbons(PAHs)with the stable benzene-ring structure,as a type of toxic organic compounds are stably distributed in various environment media.Due to the effects of carcinogenic,teratogenic,mutagenic and the features of bio-accumulation and bio-magnification of polycy'clic aromatic hydrocarbon,the existence of PAHs seriously threaten the ecological environment and human's health.How to effectively deal with PAHs has become an urgent problem to be solved.Micro-biological degradation is currently considered as one of methods that could remove PAHs with the high efficient and being environmental friendly.Through the research of the degradation capacities of Irpex lacteus F17 for phenanthrene,anthracene and fluoranthene,we compared the differences of degradation properties of phenanthrene,anthracene and fluoranthenethe,and the interaction effects among the degradation process of phenanthrene,anthracene and fluoranthene by Irpex lacteus F17 in a coexisting system were explored.At the same time,we discussed the degradation pathway's preliminarily with the analysis of intermediate products of the degradation.In order to prsovide a scientific basis for microbial remediation of PAHs,we also explored the enzymatic mechanism of the degradation of phenanthrene,anthracene and fluoranthene by Irpex lacteus F17 through the determination of enzyme activitiesThe results showed that the rates of degradation reached maximum when the initial concentrations of phenanthrene,anthracene and fluoranthene were 5 mg/L and 10 mg/L,and the degradation rate could reach at least 93%,85%,73%,respectively.However,phenanthrene,anthracene and fluoranthene with the concentrations of 20 mg/L had toxic effects on the growth of Irpex lacteus F17,which resulted in the decline of degradation rate.Phenanthrene could be degraded preferably within the range of pH 3.0-8.0,and anthracene and fluoranthene could be degraded well within the range of pH 4.0-8.0 by Irpex lacteus F17.The degradation speed and degradation rate were both lower relatively under the lower temperature of 10-20 ?.However,phenanthrene could be degraded better than anthracene and fluoranthene under the lower temperature,showing the better adaptation for lower temperature than anthracene and fluoranthene.Within the temperature range of 30-40 ?,the degradation rate increased significantly and the optimal temperature for biodegradation was 30 ?.The addition of Tween 80 can improve the degradation capacities of Irpex lacteus F17 for phenanthrene,anthracene and fluoranthene.However,the promotion effect on phenanthrene was significantly lower than that of anthracene and fluoranthene.When the concentration of Tween 80 in the culture medium was 50 mg/L,the degradation rates of phenanthrene,anthracene and fluoranthene were improved obviously,which increased 5.5%,14.6%and 14.7%,respectively.The degradation characteristics of single and mixed PAHs by Irpex lacteus F17 were studied in this paper.For single PAHs,the degradation rates of phenanthrene,anthracene and fluoranthene were 97.79%,89.28%and 81.54%,respectively after 15 days,and the degradation capacities were as follows:phenanthrene>anthracene>fluoranthene.The process of biodegradation of single PAHs followed pseudo first order reaction kinetics model.And the fitting results showed that the degradation rates were as follows:phenanthrene>anthracene>fluoranthene.The feature of competition with each other was found in the degradation of mixed PAHs.There was no significant effect on the degradation of phenanthrene with the existance of anthracene or fluoranthene in the same system,while the coexistance of phenanthrene or fluoranthene would impede the degradation of anthracene.And the coexistance of phenanthrene or anthracene would impede the degradation of fluoranthene as well.The addition of naphthalene,a kind of low-cyclic PAHs,would promote the biodegradation of high-cyclic PAHs such as anthracene and fluoranthene which was harder to be utilized by microorganism.Compared with no naphthalene in the culture medium,the degradation of anthracene and fluoranthene were raised by 23.70%and 30.25%,respectively.The result showed the characteristic of co-metabolism in the biodegradation of PAHs.The biodegradation capacity of PAHs mainly depend on molecular structure,molecular size,water solubility and biological availability.IVIn the 15-day degradation processes of phenanthrene,anthracene and fluoranthene,the enzyme activities of the three degrading enzymes could be monitored.We found that the enzyme activity of lignin peroxidase was significantly higher than the enzyme activity of manganese peroxidase and laccase in the whole degradation processes.Therefore,lignin peroxidase played a major role in the degradation processes of phenanthrene,anthracene and fluoranthene,and the enzyme activities of the three degrading enzymes were higher during the first 9 days.In the degradation processes of phenanthrene,anthracene and fluoranthene,anthracene was transformed into 9,10 anthraquinone firstly and then converted into phthalic acid under the action of enzymes.Phenanthrene was firstly converted into 1-hydroxy-2-naphthalene formic acid and then transformed into 2-(3-carboxy-3-oxo-propenyl)-benzoic acid or 4-(2-hydroxy-phenyl)-2-oxo-3-enoic acid.The former was transformed into phthalic acid,and the latter was transformed into catechol.Fluoranthene was firstly cleaved under the action of enzyme to form 1-phenylnaphthalene,followed by the generation of 1-phenylnaphthalene and 1,4-dicarboxybenzene through ring cleavage and a series of enzymatic reactions.According to the different degradation pathways of phenanthrene,anthracene and fluoranthene,we found that Irpex lacteus F17 exhibited different degradation pathways for different types of PAHs,and even showed great differences between the isomers of phenanthrene and anthracene.