Quantitative Apportionment Of Environmental Pollution Sources-oriented Risk In Yulin National Energy And Chemical Industry Base And The Enhanced Bioremediation Of Characteristic Pollutants

Yulin National Energy and Chemical Industry Base is located on the edge of Mu Us Desert,with fragile ecological environment,unique structure and function.It possesses characteristics of multi-polarization,cross-contamination and combined pollution due to its complex pollution sources,special pollution forms and diverse land use structures.Polycyclic aromatic hydrocarbons(PAHs),heavy metals and organochlorine pesticides(OCPs)have persistent residues,bioaccumulation and carcinogenicity in the environment,which are seriously harmful to human health and ecological environment safety.Surface waters and soil are important environmental receptors for pollutants such as PAHs and heavy metals,carrying loads from different sources.Knowing the pollution status,risk level and pollution source of toxic pollutants such as PAHs,heavy metals and OCPs in surface waters and soil accurately is the basis for preventing and controling of toxic pollutants in energy and chemical industry region,and also is the key to alleviate regional risk pressure and solve environmental problems.Therefore,this study takes Yulin National Energy and Chemical Industry Base as the research area,and selects various types of land in area for large-scale spatial field sampling to collect surface waters and soil samples.The concentration level,spatial distribution characteristic,sources apportionment and environmental impact caused by PAHs,heavy metals and OCPs had been deeply studied,and a quantitative apportionment modle of source contribution to environmental risk has been established,aiming at providing scientific theoretical basis for the rational control of pollution sources and the determination of key pollution control areas.Meanwhile,enhanced bioremediation method of characteristic pollutant PAHs was explored,in order to provide theoretical support and method for bioremediation of the polluted environment.The research has important practical significance for protecting the local ecological environment and building the Yulin National Energy and Chemical Industry Base into a world-class high-end,clean,environmentally friendly and safe energy and chemical base.The main research findings are as follows:(1)The distribution characteristics of 16 PAHs,8 heavy metals and 8 OCPs in the surface waters and various types of land in the Base showed that the detection rates of heavy metals in Hg,Pb,Cd and Cr were low,while levels of COD,NH4+-N,TP reached the Class III-V standards of surface waters.Phenanthrene was the most abundant PAHs in the surface waters,and the high concentrations of PAHs were mainly distributed in the surface waters near the industrial area.In the topsoil,the concentration of Σ16PAHs varied from 110.22 to 4943.13 μg/kg,which was dominated by low-ring PAHs.Due to the influence of the energy chemical industry,the concentrations of PAHs in non-sensitive areas were generally higher.Except for Pb,the heavy metals of As,Cr,Cu,Zn,Cd,Pb,Hg and Mn in the topsoil were at a higher level and had larger spatial variability.The concentration of ΣHCHs ranged from 1.66 to 8.80 μg/kg,DDTs only detected low concentrations of p,p’-DDD and p,p’-DDE,residues of OCPs were caused by historical use,accompanied by the recent input of lindane.The environmental fate of DDTs was affected by soil type,only the aerobic degradation product DDE was detected in the northern Mu Us desert area,and the anaerobic degradation product DDD was distributed in the southern loess plateau area.(2)The evaluation results of pollutant ecological risk and human health exposure in the Base indicated that concentrations of Ba P and Bb F in some sample sites exceeded the surface water safety threshold recommended by USEPA.Ba P toxicity equivalent method and biological toxicity effect interval method were used to evaluate the soil PAHs ecological risk,the results suggested that the ecological risk level of PAHs in soil was at the middle and lower level.Analysis of Geoaccumulation Index(Igeo),Contamination Index(Pi),Potential Ecological Risk Index(RI)indicated that the concentrations of Cd and Hg were accumulated to a high pollution level,and their potential ecological risk single index were also at a very high risk level.The other heavy metals were also in moderate to severe cumulative pollution levels.The human health risk of exposure to soil PAHs in the Base indicated that the health risk caused by intake pathway is higher than skin contact and inhalation route,and the total non-carcinogenic hazard level(Total-HI)of ΣPAHs were lower than the safety threshold.The total carcinogenic risk(Total-CR)ranged from 2.63×10-7 to 5.99×10-6 with exceeded the acceptable level at the sampling sites in the industrial area.The Total-CR exposed to soil heavy metals in the Base was significantly higher than the acceptable level of 10-6,the Total-HI was also higher than the safety threshold.The human health exposure risk of the downtown sampling site was the highest in the whole Base.(3)The PMF-Total-CR/HI and PMF-RI coupling methods were developed in this research and applied to quantitatively characterize the ecological risks and human health exposure risk for various pollutant source categories.Compared with the PCA-MLR model,the PMF model is more suitable receptor pollution source apportionment model.Source apportionment results indicated that there were four sources of PAHs,including coke oven emission(34 %),coal combustion(33 %),wood combustion(22 %),and vehicular emission(11 %),and the dominant contribution to heavy metals was from coal related activities(52.5 %),followed by industrial activities(22.0 %),traffic activity(13.2 %)and agricultural activity(12.3 %).The relative contribution rates of PAHs source,coke oven emission,coal combustion,wood combustion,and vehicular emission to Total-CR were 38 %,31 %,13 %,and 18 %,respectively.The relative contribution rates to Total-HI were 36 %,39 %,11 % and 14 %,respectively.The heavy metals source from industrial activities contributed the largest proportion of Total-CR,and the coal-related activities source was the largest contributor to RI and Total-HI.In addition,the largest source of contribution to the pollutant concentration don’t necessarily contribute the most to the environment risk.(4)In order to reduce the risk level of characteristic pollutants,pyrene(four rings)was taken as a typical research object to study enhanced bioremediation method of PAHs polluted environment.A high efficient degradation strain was isolated from environment and named Rhodococcus ruber L9,and when the strain was cultured for 24 h to 48 h under the condition that 10 mg/L of pyrene as the sole carbon source,the degradation rate was the fastest.The higher activity of catechol 1,2 dioxygenase(C12O)was detected at 48 h,and the degradation rate of pyrene by L9 reached 61.49 % after 120 h.The molecular weight distribution characteristic of the crude enzyme showed that the strain was sensitive to pyrene before 48 h,and hence the molecular weight distribution evolved obviously,while after 48 h,the evolution trend got stable,the substances with molecular weight between 43 k D and 150 k D were decreased,and with molecular weight greater than 670 k D were increased.The degradation efficiency of pyrene by strain Rhodococcus ruber L9 can be significantly improved with the addition of electron acceptor iron ion.At 120 h,the degradation rate of pyrene with an initial concentration of 10 mg/L reached 76.02 %,and the activity of C12 O of addition of iron ion is 1.60 times of that without iron ions.The speculative mechanism of iron ion promotion biodegradation is that the interaction between iron ions and pyrene is via electron acceptor-donor,the electrons density of pyrene molecular is reduced due to the interaction,which is beneficial to its migration to the cell surface,then the cell is stimulated by the pyrene entered the cell to secret biodegrading enzymes,therefore,the metabolic rate of pyrene is speeded up.The results of biotoxicity test showed that the strain Rhodococcus ruber L9 could reduce the toxicity risk of phenanthrene and pyrene with concentration of 1.5 mg/L by 92.81 % and 72.90 %,respectively,after 60 h.The environmental safety of the strain such as antibiotic resistance and genotoxicity was evaluated,results showed that the strain was environmentally friendly and can be used for bioremediation of polluted environment.