Study On Pollution Characteristics Of Phthalic Acid Esters In Agricultural Soil And It's Microbial Remediation In Yinchuan City

Phthalic acid esters(PAEs)are widely used as plasticizers in various products,and they are easily released into the environment during the manufacture and use.PAEs have potential carcinogenic,teratogenic and mutagenic effects and are a class of typical environmental endocrine disruptors,and which will pose a serious threat to human health.The Yinchuan plain is located in the arid and semi-arid area in northwest China,although the ecological environment is relatively fragile,but the soil types are diverse and fertile,which is very suitable for the development of agricultural production and the growth of various economic crops.With the rapid development of urbanization,industrialization and modernization,the extensive use of such as plastic films,pesticides,fertilizes and expand of the scope sewage irrigation,bring greater threat to the soil environment,but current many researches focus on heavy metals,polycyclic aromatic hydrocarbons and organochlorine pesticides about soil environment,while there also has not research been carried out systematically about soil organic pollutants,such as PAEs.Therefore,this study collected different types agricultural soil samples in Yinchuan city,pollution characteristics,percentage composition and source of 16 types PAEs were analyzed by gas chromatography and mass spectrometer,as well as the potential health risk exposures to residents of six priority control phthalates by the United States Environmental Protection Agency(US EPA)were assessed.In order to further study the microbial remediation of major PAEs pollutants in soil,Dimethyl phthalate(DMP),Dibutyl phthalate(DnBP)and Diethyl hexyl phthalate(DEHP)which are major PAEs pollutants in agricultural soil of Yinchuan city,were selected as target pollutants.A strain,named MB1,was isolated from facility vegetable soil by culture enrichment method.And which can simultaneously utilize DMP,DnBP and DEHP as the sole source of carbon and energy.Then the optimal degradation conditions of the strain were obtained by orthogonal experiment design.And growth curve,degradation curve of the strain were investigated in optimal.degradation conditions.Finally,the strain MB1 to phthalic acid esters degradation characteristics in artificially contaminated soil was researched in culture incubation.It provides a certain theoretical basis for the soil PAEs pollution remediation in this area.The result shows that:(1)The total PAEs concentrations range from 0.391 to 11.924 mg·kg-1 in soils,with the average and median concentration being 4.277 and 4.427 mg·kg-1 respectively.Compared to other areas,it is at moderate pollution levels.The concentrations of PAEs in different types land are also different.The average concentration of ?16PAEs and ?6PAEs are successively from high to low:facility vegetable land,followed by the mulched farmland,woodland,unmulched farmland,orchard and grassland.(2)Among the sixteen PAEs congeners,Diphenyl phthalate(DpHP)is not detected in all soil samples,DMP,Diethyl phthalate(DEP),DnBP,Diisobutyl phthalate(DIBP),DEHP are detected in all soil samples and the detection rates of these compounds all are one hundred percent.DMP is the most abundant component,which account for 44.64%of the total PAEs,followed by DnBP and DEHP,and the average contributed rates are 21.25%and 23.34%respectively.The sum of DMP,DnBP and DEHP account for 89.23%of the contents of ?16PAEs.(3)The source of PAEs in agricultural soil was analyzed by correlation analysis and principal component analysis.The homologues of DIBP,DnBP,Di-n-octyl phthalate(DnOP),Bis(4-methyl-2-pentyl)phthalate(BMPP)and Di-nonyl phthalate(DNP)have significant correlation(r=0.84?0.97),which mainly come from plasticizers and are most widely used in the industrial production of plastic polymers.The correlation of DMP,DEP,Bis(2-butoxyethyl)DBEP,Bis(2-ethoxyethyl)DEEP and Diamyl phthalate(DPP)are significant(r=0.84-0.90),which mainly come from the use of fertilizers,pesticides and insecticides.The correlation between DEHP and Dicyclohexyl phthalate(DCHP)are significant(r=0.71),which mainly used as plasticizer and also widely used in the production of various plastic products.(4)The human health risk assessment indicates that the non-carcinogenic risks of phthalates monomers via dietary and non-dietary approaches in this study are within an acceptable range.The carcinogenic risks of DEHP and Butyl Benzyl phthalate(BBP)via non-dietary routes to human health are within an acceptable range.However,The carcinogenic risks range to human health of DEHP via dietary route are 7.39 ×10-7?2.9×10-5,with an average value of(1.03±0.77)×10-5,which the average value is higher than the recommended value set by the US EPA,and 40%of soil samples show that DEHP present certain cancer risk through dietary pathway,therefore it should receive more attention.(5)A bacterial strain MB 1 which can utilize DMP,DnBP and DEHP as the sole source of carbon and energy.The strain,is isolated by culture enrichment method from facility vegetable pollutant soil.Based on the morphology,physiological characteristic and 16S rDNA sequence analysis,MB1 is identified as Microbacterium sp.The results show that the optimized degradation condition is pH=8,temperature 25?,inoculum size(V/V)5%and 300 mg·L-1 of original PAEs concentration.Under the optimal condition,the strain present S curve growth,and the degradation rates of DMP,DnBP and DEHP in mineral salt medium after 7 days are 99.62%%,99.65%and 55.26%,respectively.(6)Adding the strain and CK in artificially contaminated soil with the concentrations of DMP,DnBP and DEHP are all 50 mg-kg-1,shows that the degradation rates of DMP,DnBP and DEHP are 3.86%,4.19%and 2.01%in the sterilized soil and are 4.82%,5.99%and 3.44%in the unsterilized soil without adding strain after 21 days,respectively.The strain MB1 degrades phthalates effect in unsterilized soil is slightly higher than sterilized soil,and indigenous microbes can degrade only a small amount of PAEs in soil.The degradation rates DMP,DnBP and DEHP are 94.45%,95.65%and 39.21%in sterilized soil and are 94.93%,95.99%and 41.16%in unsterilized soil by adding strain after 21 days,respectively.The strain MB1 has a certain ability to repaire a variety of PAEs contaminants in soil.