| In the context of raising extraction and usage of petroleum in China,the process of petroleum transportation,processing and storage has witnessed a significant aggravation of environmental pollution caused by leakage accidents as a result of improper operations.It is quite difficult to monitor the environment and control pollution at the Loess Plateau,a principal petroleum-producing region in China,due to its special geographical location and complicated environmental conditions.Polycyclic aromatic hydrocarbons(PAHs),one of the main components of petroleum,poses an enormous threat to human health and the ecological environment for its significant "tri-effect"(teratogenic,carcinogenic and mutagenic),drawing increasing attention to pollution caused by PAHs in petroleum.In this study,which targets at the soil of the petroleum exploitation area at the Loess Plateau,the content of 16 PAHs with priority given by the United States Environmental Protection Agency(USEPA)is measured with a triple quadrupole gas chromatograph-mass spectrometer(GC-MS/MS),the composition characteristics and vertical distribution characteristics of PAHs in soil at different depth(0-10 cm,10-30 cm and 30-50 cm)are identified with possible sources analyzed,and the resulting ecological and health risks are evaluated;in a 150-day soil culture experiment of this study,the mechanism of remedying PAHs-contaminated soil by four kinds of materials,including bacterial manure,organic fertilizer,peat and Pisha sandstone,is explored;the changes in the soil microbial community structure and diversity during restoration by bacterial manure are analyzed by means of high-throughput sequencing technology;and the effects of various remediation materials on removal of soil against PAHs are verified by virtue of pot experiment.This study,which plays a significant role in protecting the soil environment of the study area and maintaining sustainable and sound development of the petroleum exploitation industry,is expected to lay a theoretical basis for the remediation of PAHs-contaminated sites in the future.The main results of this study are as follows:(1)The analysis of 60 soil samples indicate that the detection rate of 15 PAHs except for Acenaphthylene(ACY)is up to 100%.The average contents of 16PAHs(?16PAHs)in soil at depth of 0-10 cm,10-30 cm and 30-50 cm are 5502.44 ?g/kg,2292.94 ?g/kg and 2203.88 ?g/kg,respectively.The average contents of carcinogenic PAHs(?7PAHs)in the corresponding soil layers accounted for 33.30%,40.12% and 47.15% of 16 PAHs,respectively.Compared with other regions at home and abroad,the PAHs content in the soil of this study area is relatively higher.(2)The vertical distribution laws of ?16PAHs and ?7PAHs in the soil of the study area are basically consistent,and their concentrations gradually decrease with the increase of the soil depth,and the decline rates are 59.95% and 43.30%,respectively.The three individual PAHs of Fluorene(FLU),Phenanthrene(PHE)and Chrysene(CHR)have the largest proportions of decline with 71.53%,85.10% and 53.87 %,respectively.The proportion of PAHs rings in the soil at different depths are similar.To be specific,3-ring and 4-ring PAHs account for a larger proportion in each depth of soil.(3)The sources of PAHs in the soil at different depths in the study area vary slightly.To be specific,petroleum source has the paramount contribution to the total amount of PAHs(37.57%)in soil at depth 0-10 cm,while biomass burning(28.05%)and coal/coke burning(35.61%)sources have the paramount contribution in soil at depths 10-30 cm and 30-50 cm.What's more,the source of vehicle traffic accounts for a large proportion in each soil layer.(4)Results of ecological risk analysis indicate that the soil at depths 0-10 cm and 30-50 cm is at high risk,while that at depth 10-30 cm is at medium risk.Individually speaking,Fluorene(FLU)and Pyrene(PYR),which are of high risk in the soil at different depths.Results of health risk analysis indicate that there are potential carcinogenic risks in the soil at different depths in the study area.In terms of exposure pathways,the ranks of three exposure pathways in carcinogenic risk are: dermal contact> soil ingestion> inhalation;from the perspective of age,PAHs pollution of soil poses a greater health threat to adults than children and adolescents;from the perspective of gender,carcinogenic value-at-risk for female is generally higher than that for male.(5)In the soil with high initial concentration of PAHs,the removal rates of 16 PAHs of blank control,bacterial manure,organic fertilizer,peat and Pisha sandstone treatments are 23.91%,66.78%,51.17%,54.52% and 42.99%,respectively;the removal rates of 16 PAHs by each treatment in the soil with low initial concentration of PAHs are 11.42%,66.06%,53.37%,53.30% and 43.83%,respectively.Compared with the blank control group,the treatments of other four groups can facilitate the removal of PAHs significantly.The group in which bacterial manure is applied has the highest removal rate of PAHs and the group in which Pisha sandstone is applied has the lowest removal rate of PAHs;moreover,the removal rates of 16 PAHs by each treatment in LMWPAHs are significantly higher than those of HMWPAHs.(6)Compared with natural remediation,the microbial community structure in soil in which bacterial manure is applied is changed significantly.Among the top 13 phylum categories,Proteobacteria,Firmicutes,Bacteroidetes and Actinobacteria are positively related to the removal rates of LMWPAHs,HMWPAHs and 16 PAHs.To be specific,Actinobacteria shows highly significant positive correlation to the removal rates of PAHs(p<0.01),indicating that Actinobacteria is the dominant phylum for removing PAHs in the process of remediation with bacterial manure.Compared with PAHs-contaminated soil,soil remediated with bacterial manure,organic fertilizer,peat and Pisha sandstone is more conducive to the growth of ryegrass(Lolium multiflorum Lam),whose plant height,biomass and leaf SPAD value are significantly improved.The three indicators are all sensitive in indicating the ecological toxicity of PAHs-contaminated soil. |
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