Bacterial Degradation Characteristics Of 1-methylphenanthrene And Toxic Effects Of Its Degradation Metabolite

Alkylated polycyclic aromatic hydrocarbons(A-PAHs)are polycyclic aromatic hydrocarbons(PAHs)with alkyl side chains,which are persistent organic pollutants widely existing in the environment.A-PAHs are important components of total polycyclic aromatic hydrocarbons in crude oil polluted environment.At present,microbial degradation is the main way to remove A-PAHs in the environment,and bacterial degradation has attracted more attention.A-PAHs may be transformed into potential toxic intermediates during microbial metabolism,which may affect the aquatic ecological environment.However,there is still lack of researches on the ecotoxic effects of A-PAHs intermediates.In this study,the degradation characteristics and degradation pathways of 1-methylphenanthrene by Novosphingobium sp.SA925 was investigated.At the same time,the effects of 1-methylphenanthrene and its intermediate metabolite(1-phenanthrenecarboxylic acid)on the growth,photosynthesis and antioxidant enzyme system of microalgae were investigated.The green microalgae Raphidocelis subcapitata was adopted as the testing organism.The main results are as follows:(1)The degradation efficiency of 1-methylphenanthrene by the strain SA925 was ranged from 56%to 100%at the concentration of 0-20 mg·L^-1 for 1-methylphenanthrene,p H value of 6.5-9.0 and salinity of 0%to 3%after 2 day incubation.1-methylphenanthrene was initially oxidized via two different biochemical strategies.On one hand,1-methylphenanthrene was degraded through the monooxidation of the methyl group;on the other hand,1-methylphenanthrene was degraded through the dioxygenation on the no-methylated benzene ring.The dioxygenation of C5,6-position of 1-methylphenanthrene was the most important pathway of 1-methylphenanthrene degradation by strain SA925.(2)Eight PAHs were detected in the crude oil polluted water,and the total PAHs content was 5095.23±438.82 ng·L^-1.The A-PAHs content accounted for 57.90%of the T-PAHs content,and the removal rate of T-PAHs by strain SA925 to crude oil polluted water was 30.71%after 7 days.Glucose could promote the degradation efficiency of 1-methylphenanthrene by the strain of SA925,and the degradation percentage was increased from 43.3%to 96.5%after12 h.However,n-hexadecane and cyclohexane would inhibit the biodegradation capacity of the strain SA925.(3)The 96 h-EC₅₀ of 1-methylphenanthrene and 1-phenanthrenecarboxylic acid with microalgae Raphidocelis subcapitata were 0.343 and 0.627 mg·L^-1,respectively.Under different concentrations of 1-methylphenanthrene and 1-phenanthrenecarboxylic acid,the photosynthetic and antioxidant enzyme system of Raphidocelis subcapitata were damaged with different degrees,and the contents of CAT,SOD and MDA in microalgae were increased,and the changes of indexes in the high concentration group were more obvious than those in the low and medium concentration groups.The variation range of each index in the 1-methylphenanthrene treatment group was greater than that in the 1-phenanthrenecarboxylic acid treatment group,indicating that Raphidocelis subcapitata was more sensitive to 1-methylphenanthrene stress.