A Study On Biodegradation Of Several Phas In Estury Sediment

Polycyclic Aromatic Hydrocarbons (PAHs) are ubiquitous contaminants in the enviroment, known for their carcinogenic, teratogenic and mutagenic properties. Because of their persistence in environment and their bioaccumulation, as well as their potential hazards to human health and ecological environment, PAHs received worldwide scientific concerns. PAHs in the environment are removed through many approaches, such as photodegradation, chemical degradation, and biodegradation et al.Phenanthrene(Phe), anthracene(Anth), pyrene(Pyr) and chrysene(Chry) are selected as target pollutants in this study. Phe and Anth are three–ring PAHs with typical K- and Bay-region structure, which is considered as responsible for their carcinogen. Pyr and Chry are four–ring PAHs widely existed in environment. They are usually indicators for PAHs pollution.To study the environmental behavior and fate of PAHs, a labotory microcosm system was used for aerobic biodegradation of Phe, Anth, Pyr and Chry by natural microbial community with LiCun estuary sediment, which is highly polluted, as the incubation substrate. The degradation mechanism was also investigated. Major results and conclusions are as follows:(1) A purification protocol using thin layer chromatography (TLC) combined with column chromatography, following an ultrasonic extraction, for determination of PAHs (Phe, Anth, Pyr and Chry) in LiCun estuary sediment was proposed. The conditions of sample extraction, column chromatography, and TLC were optimized. Under the best conditions, the recoveries of four target compounds for spiked blanks were 76.9%⁹0.1%, with RSD ranged from 4.11%⁷.74%. The recoveries of four target compounds for spiked matrices were 72.7%⁸8.7%, with RSD ranged from 4.50%⁶.57%. The results basically met the requirements of USEPA standard. (2) It was shown, from a 6-month aerobic incubation experiment, that in the control experiments the concentrations of Phe, Anth, Pyr, Chry decreased from 569 ng·g^-1, 72.1 ng·g^-1, 408 ng·g^-1, 230 ng·g^-1 to 423 ng·g^-1, 68.0 ng·g^-1, 343 ng·g^-1 and 212 ng·g^-1, respectively, corresponding to degradation percentages of 25.6%, 5.70%, 16.1% and 7.80%, respectively. The degradation rate of the four PAHs decreases in the order of Phe, Pyr, Chry, Anth. This is mainly related to the background concentration, structure and water solubility. In spiked experiment the concentrations of Phe, Anth, Pyr, Chry decreased from 641 ng·g^-1, 208 ng·g^-1, 485 ng·g^-1, 395 ng·g^-1 to 437 ng·g^-1, 168 ng·g^-1, 385 ng·g^-1 and 337 ng·g^-1, corresponding degradation percentages were 31.8%, 19.2%, 20.6% and 14.8%, respectively. The degradation rate of PAHs increased obviously in spiked sediment, this was because the PAHs added supplied abundant carbon source for the strains, which gradually became the dominant strains after induction and domestication.(3) Four strains were isolated from LiCun esturary sediment, and aerobic biodegradation of PAHs in liquid substrate containing the four strains were investigated. The degradation rate of the four PAHs were 91.7%, 85.7%, 79.6% and 70.0%,which were obviously higher than those observed under natural microbial consortium. The biodegradation process of PAHs degraded by domestic consortium undergo induction, stabilization and slow degradation stage, which is similar to that degraded by natural consortium, while the degradation period is greatly reduced. Isotopic fractionation was obviously observed, as evidenced by the CSIA results of PAHs in biodegradation.(4) The degradation pathways of Phe and Anth were investigated by combining CSIA with GC-MS. The degradation pathway of Phe is as follows: Firstly Phe is transformed to cis-3,4-dihydrodiols by dioxygenase, then cis-3,4-dihydrodiols is transformed to 3,4-dihydroxyphenanthrene and 1-hydroxy-2-naphthoic acid (1H2N) in sequence, finally 1H2N is degraded to 1,2-benzenedicarboxylic acid and 2-hydroxybenzoic acid respectively. The degradation pathway of Anth is as follows: Firstly Anth is transformed to anthrone and 9,10-anthracenedione in sequence, then 9,10-anthracenedione is degraded to aromatic acid and ester, finally they are transformed to small molecule acid.