| Polycyclic Aromatic Hydrocarbons (PAHs) are ubiquitous contaminants in the environment, known for their carcinogenic, teratogenic and mutagenic properties. Because of their toxicity, bioaccumulation, semi-volatility and persistence, PAHs are recognized as Persistent Organic Pollutants (POPs) and received worldwide scientific concerns. The sources of PAHs are very broad, but are mostly anthropogenic. PAHs in atmosphere and water tend to accumulate on the particles, and finally deposit into ground and sediment. In addition to posing threats to human health and terrestrial ecosystem, PAHs can also seriously affect aquatic and benthic organiams. PAHs in the environment can be eliminated by a variety of ways, such as microbial degradation, chemical degradation and photodegradation. In sedimentary environment, biodegradation is the major one, through which PAHs could be transformed, and ideally, completely mineralized to produce CO2, H2O and other inorganic small-molecular compounds, thus to entirely eliminated the pollution of PAHs.Anthracene(AC) is a common three-ring low-molecular-weight PAH. AC and its degradation products usually are nontoxic to human, but due to its structural resemblance to moieties of carcinogenic PAHs, such as BaP and BaA, it is often selected as a model compound. Methyl-substituted anthracene is a widely existing pollutant in the envirnment. Methyl-substituted anthracene is believed to be biologically inactive for mutagenicity and carcinogenicity, while dimethyl-substituted derivative, 9,10-dimethyl anthracene,can be transformed to epoxide with"bay area"structure, which is bioactive for tumor mutation and cell aberrance.In this thesis, AC, 9-methyl anthracene (9-MA) and 9,10-dimethyl anthracene (9,10-DMA) were selected as model compounds, and LiCun esturary sediment, the incubation substrate, to investigate the aerobic biodegradation of these anthracenes using a labotory microcosm system. The aims were to obtain the degradation rates and to determin the possible degradation products (intermediates). Major results and conclusions are as follows:(1) A laboratory microcosm system with controlled oxic or anoxic conditions was set up for investigation of biodegradation of organic pollutants in sediment.(2) The environmental parameters, including those of overlaying seawater and sediment porewater, were determined before incubation experiment. It was shown that pH, salinity and dissolved oxygen concentration of seawater were 7.46, 31.794 and 4.27mg·L-1, respectively, and concentrations of potential electron acceptors such as Fe3+, SO42-and NO3- , in sediment porewater were severally 4.26mg·L-1, 1156mg·L-1and 2.58mg·L-1. The redox potential and the content of total organic carbon in sediment were -280.4mV and 1.54%. These parameters indicated that, LiCun estuary sediment was principally in a reduced environment and the organic matter in this region was chiefly anthropogenic.(3) Gas chromatography-hydrogen flame ionization detection (GC-FID) was chosen to detect targeted pollutants and their possible degradation products in sediment samples. The chromatography conditions were optimized, under which the recoveries of AC, 9-MA and 9,10-DMA for spiked blanks were 79.5~83.79%, with RSD ranged from 4.61 to 14.78%; and the recoveries of AC, 9-MA and 9,10-DMA for spiked matrices were 66.20~82.95%, with RSD ranged from 3.34% to 6.19%. Meanwhile the pretreatment process of the sediment samples was optimized, and the recoveries for column chromatographic purification eluted by hexane/toluene and hexane/dichloromethane were compared with special attention. Mixture of hexane/toluene with equal volume was selected for its higher recovery, although it has a lower volatility and thus harder for solvent replacement.(4) The background value of AC was determined to be 32.88ng·g-1, while no 9-MA and 9,10-DMA was detected. It was shown, from a 6-month aerobic incubation experiment, that the concentration of AC decreased from 32.88ng·g-1 to 32.32ng·g-1 in the control experiment, corresponding to a degradation percentage of 1.70%. However, the degradation percentage of the spiked AC was 11.17%, with concentration reduced from 170.40 ng·g-1 to 151.36 ng·g-1. For spiked 9-MA and 9,10-DMA samples, the concentration were declined from the initial values of 133.84 and 144.26ng·g-1 to 120.50 and 135.18ng·g-1, respectively, accounting for degradation percentages of 8.46% and 6.33% separately. According to the high background of AC, it was inferred that LiCun estuary might has been severely polluted by PAHs. Different degradation percentages of the three targeted pollutants under the same condition indicated that methyl-substitution resulted in higher persistence of AC in sedimentary environment with lower natural attenuation rate.Even though no degradation product or intermediate was detected, the results of this work are helpful for raising awareness to the pollution of PAHs, and may also provide guidance and reference for pollution combating and decision-making for environmental agency.
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