Study On The Occurrence Characteristics And Bio-degradation Of PAHs In The Yangtze River Estuary

Polycyclic aromatic hydrocarbons?PAHs?are widespread typical persistent organic pollutants which are highly toxic to living organisms.Located in the critical transitional zone between land and sea,the estuarine and coastal area is influenced by complex hydrodynamic conditions and intense human activities.The existence of natural environmental gradients caused by combined pollution of PAHs and other contaminants,hydrodynamic condition,sediment transport and material exchange in estuaries makes them ideal niches for studying microbial response to environmental factors especially pollutants.Even though many researchers have studied the concentration,pollution level,multimedia distribution,source apportionment and ecological/health risk of PAHs for estuaries,gaps in understanding remain with respect to the inherent linkage between pollutants and accommodated microbes,the effects of pollutants on microbial communities and influence of combined pollution on the microbial degradation of PAHs in the estuary area.Yangtze River Estuary was chosen as the study area.In the basis of the pollution level of PAHs in multimedia,the composition,diversity and distribution of the microbial community and the impact of pollutants and environmental parameters on microbial communities and their bioremediation implications were explored.Furthermore,PAHs degrading bacteria were isolated from the sediment samples.These bacteria have proven to be effective in degradation of PAHs.Further study has been done systematically on the the effect of heavy metal and nano particles on the biodegradation of Phe.The main results were as follows:?1?For the Yangtze Estuary,the mean concentrations of PAHs were suspended particulate matter(8922.9 ng g^-1)>sediments(2400.2 ng g^-1)>water(1042.9 ng L^-1).PAH concentrations in three phases were higher in dry seasons?January and April?than in rainy seasons?July and October?,and showed a distribution pattern as freshwater area>transition area>seawater area.TOC and BC_Crr were crucial controlling factors for the sorption and distribution of PAHs.?2?The dominant bacterial phyla of all sediment samples in the Yangtze River Estuary were:Proteobacteria,Bacteroidetes,Chloroflexi,Acidobacteria,Firmicutes and Nitrospirae.Influenced by the salinity gradient of the estuary area seawater sediments and freshwater sediments presented distinct microbial groups.Total Phosphorus,Salinity,PAHs,Cu,Cr,Pb,Total Organic Carbon,Ni,and pH values were crucial factors for the spatial-temporal distribution of the total community.Compared with the bacteria in seawater area and transition area,bacteria living predominantly in freshwater areas survived with higher concentrations of pollutants were more accommodated to these pollutants;Dominant PAH degrades in sediment samples were:Alcaligenaceae_uncultured,Comamonadaceae_unclassified and Xanthomonadales_uncultured?freshwater area?;Burkholderiaceae_unclassified,Xanthomonadales_unclassified,Deltaproteobacteria_unclassified,Flavobacteriaceae_unclassified and Bacillus?seawater area?;Pseudomonas and Flavobacterium were more or less evenly distributed in all sampling areas.Estuarine sediments in July have more PAH degraders and may thus possess high PAH-degrading potential.TPAHs,Cu,salinity and pH values were key influencing factors for PAH degraders.?3?Thirty-four PAHs-degrading strains were isolated from the sediment samples collected from the Yangtze estuary and coastal areas.Strains were identified as Alicyclobacillus,Bacillus,Enterobacter,Klebsiella,Microbacterium,Proteus and Pseudomonas with respect to their 16S rDNA sequence and phylogenetic analysis.These isolated PAHs-degrading strains showed high degradation ability to PAHs.The degradation efficiency of TPAHs by these strains was 3-rings>2-rings>4-rings>5-rings?6-rings.?4?Alicyclobacillus sp.BS-17 could metabolize Phenanthrene?Phe?through protocatechuate route and coexisted Zn or nano ZnO did not influence the biodegradatioin pathway.Degradation efficiency of Phe was studied till 35 days of incubation and the biodegradation phases of Phe by Alicyclobacillus sp.BS-17 were biphasic dissipation?fast-slow in process?.Rapid degradation of Phe was observed from 0^thh to 8^thh day?faster first phase?.Subsequently,the rate of microbial degradation of Phe gradually slowed down and tended to stagnate,from 8^thh to 35^thh day?lower second phase?.The half-life of Phe gradually increased over time throughout the incubation process.Compared with the first dissipation phase,the half-life of Phe for the second dissipation phase increased from 31.51 h to 139.52 h.?5?Zn²⁺and nano ZnO could influence the biodegradation of Phe to different degrees,Phe-degrading ability of Alicyclobacillus sp.BS-17 were inhibited at relatively lower concentrations(10?g L^-1)of Zn²⁺but no significant inhibition on the process of biodegradation of Phe at higher concentrations of Zn²⁺;Phe-degrading ability of Alicyclobacillus sp.BS-17 were inhibited by nano ZnO from 0^thh to 6^thh day and recovered soon.Nano ZnO may help the process of Phe biodegradation and the Phe biodegradation rates increased from low to high concentrations of Nano ZnO(10 to 1000?g L^-1),which may be due to the capability of adsorption and catalysis of the nano material.This study discussed the effects of pollutants and environmental parameters on the composition,diversity and distribution characteristics of microbial communities in the sediments of Yangtze Estuary,and studied the impact of heavy metals and nanomaterials in normal environment concentration on bio-degradation of PAHs by PAHs-degrading strains isolated from the sediment samples collected from the Yangtze estuary.This research might enriches the relevant theory of the fate of PAHs in estuarine environment affected by various pollutants.Besides this,these results might provide theoretical basis for the pollution prevention and control of the Yangtze river and the Yangtze river delta region.