| Phthalate?PAEs?pollution caused by the use of mulch film began to be serious.Plastic film planting technology has been widely promoted in arid and semi-arid areas in northwest China because of its function of retaining water and increasing production.The environmental risk of PAEs brought by this planting model needs to be paid enough attention.Plant root exudates have been proven to have a positive effect on promoting degradation of various organic pollutants?polycyclic aromatic hydrocarbons,PCBs,etc.?in the soil.Therefore,this study takes agricultural soil in arid areas as a research object and uses field experiments to analyze the cumulative effect of PAEs in soil caused by the type of mulch film,the treatment of mulch film and the years of mulching.At the same time,through indoor control experiments to analyze the effect of the addition of corn artificial root exudates on the microbial activity and biological properties of DBP-contaminated soil,and to clarify the mechanism of root exudates degradation of soil DBP.It is expected to provide a theoretical basis for objectively evaluating the cumulative risk of PAEs in soil,the remediation of PAEs contaminated soil,and the safe use of mulch.The results indicated that:1.The PAEs content of the five biodegradable mulches was higher than that of PE mulch.There are 5 kinds of PAEs added to the mulch:DBP,DEHP,DEP,DMP and DnOP,among which DBP and DEHP have higher content.Compared with the control soil,the use of mulch film resulted in a significant increase in PAEs content in the soil,and the content of DBP in the mulch film had a significant positive correlation with the soil PAEs content.Therefore,the risk of PAEs pollution behind biodegradable mulch film degradability should be concerned.2.Both plastic film exposure and plastic film landfill treatment resulted in an increase in PAEs content compared to unfilmed soil.The content of PAEs homologues in soil detection from high to low is DBP>DEHP>DEP>DMP>DnOP,and the detection amount and detection rate of DBP and DEHP are higher.DBP has been detected in all soil samples and its content has exceeded the soil allowable concentration by?USEPA?.Compared with exposure treatment,plastic film landfill treatment will result in higher accumulation of soil PAEs.The long-term mulching experiment showed that it was difficult for the soil to completely degrade PAEs.Perennial mulching would cause continuous pollution of PAEs and a significant increase in soil PAEs content.With the absence of environmentally friendly plasticizers,even degradable mulches need to be reclaimed from the soil to reduce the environmental risk of PAEs caused by mulching.3.The treatment of corn root exudate solution has a significant effect on soil enzyme activity.Different amounts of AREs all promoted the respiration of the soil,and the high concentration of DBP treatment has a significant inhibitory effect on the respiration of the soil.At different DBP levels,the treatment of AREs with the addition of 2mg/d and 10mg/d significantly enhanced the activity of FDA enzymes and?-glucosidase,while the treatment with the addition of AREs of 50mg/d significantly inhibited their activity.Polyphenol oxidase activity is more sensitive to DBP pollution concentration.The high concentration of DBP(100mg·kg-1)treatment resulted in lower initial polyphenol oxidase activity.However,with the extension of the cultivation time,the high concentration of DBP treatment led to a slight rise in enzyme activity.The treatment of DBP has a toxic effect on soil enzyme activity,and the addition of AREs can alleviate the adverse effects of DBP on soil microorganisms.4.The addition of AREs in the soil with different concentrations of DBP contaminated soil has a significant effect on the contents of three chemical morphological components of DBP?desorption component,non-desorption component and combined residual component?.The increase in the amount of AREs added on the fifth day of soil cultivation led to an increase in the content of bound residual components and a decrease in the content of desorption components in the soil.In contrast,the greater the amount of AREs added,the lower the content of combined residual components in the soil after 60 days of cultivation.The additions of AREs promoted the DBP desorption in soil and improved the bioavailability of soil DBP.In addition,due to the increase of soil enzyme activity,the biodegradation of DBP desorption components was promoted.The presence of root exudates can alleviate the cumulative risk of soil PAEs. |
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