The Detrimental Effects Of DEHP On Soil CO₂ Emission And Nitrification In Calcareous Soil By Fenton-like Reaction Combined With Na₂S₂O₃

Plastic film mulch is widely used to increase temperature and moisture contents of soil inorder to increase crops yield.Phthalates(PAEs)are primarily used as plasticizers,substances added to plastic to increase their flexibility and longevity.Phthalates(PAEs)contents in plastic make up about 10-60% of its total mass,this concentration of di(2-Ethylhexyl)phthalate(DEHP)can result into an organic pollutant.DEHP are persistent pollutants,when released into the environment,accumulated DEHP may have a negative effect on soil carbon(C),nitrogen(N),phosphorus(P)and nutrient cycle.Due to wide use if plastic films mulch,DEHP have been detected in different agricultural soil types including vegetable fields and cotton fields.It has been discovered that DEHP may have a detrimental effect on overall soil health and soil microbiodiversity,therefore,DEHP pollution issue and mitigation has drawn a lot of attention in recent times.Calcareous soil is a widely distributed in soil type in dry and semi-arid areas in China.At present,studies that have been done to understand mechanisms related to DEHP effect on soil nitrogen transformation process in calcareous soil is very limited,therefore this research was conducted to carefully study the effect of different dosage of DEHP on soil nitrogen Cycle,microbial characteristics and CO2 emission.Our research aims to reveal the characteristics of soil nitrogen transformation and the response of greenhouse gas emission to DEHP exposure.Our research used modified Fenton’s reaction remediation method to preliminarily investigate the effect of DEHP remediation on microbial community.This experiment design included: 1)control CK(treated with citric acid only),2)CH(containing high concentration DEHP 100mg/kg1 + citric acid),3)CHF(containing high concentration DEHP 100mg/kg1 + ferrous sulfate(Fe SO4)+ citric acid),4)CHCO(containing high concentration DEHP 100mg/kg1 + sodium thiosulfate(Na3S2O3)+ citric acid),and CHCOF(containing DEHP 100mg/kg1 + sodium thiosulfate(Na3S2O3)+ ferrous sulfate(Fe SO4)+ citric acid at a ratio 20:10:10).An incubation experiment was conducted using flow-based injection analyzer to determine different forms of Nitrogen and using GC-MS to determine DEHP biodegradation rate without Fenton’s Oxidation.This experiment design included: 1)CK(untreated control),2)Urea alone(incorporated with a 100% urea N only),3)Urea + DEHP10(incorporated with 100% Urea and DEHP 10mg/kg),and 4)Urea + DEHP100(incorporated with 100% Urea and DEHP 100mg/kg).We also used the enzymatic method to investigate DEHP effects on nitrification related enzyme activities(nitrate reductase,hydroxylamine oxidoreductase(HAO)).The Picarro(G2508)was use for our N2 O and CO2 emission fluxes.Our preliminary results were as follows:The soil ammonium nitrogen(NH4+-N)increased with time and later decreased rapidly after 3-43 days of incubation and soil nitric nitrogen(NO3 – N)concentration in 100mg/kg treatment was significantly lower than urea alone treatment.10-100 mg/kg-1 DEHP had a stronger inhibitory reaction on soil potential nitrification rate(PNR)compared with urea alone treatment.The ammonium nitrogen(NH4+-N)in samples containing 10mg/kg-1 and 100mg/kg-1 increased at the peak of emission by 7.0% and 18.6% respectively.DEHP had an inhibitory effect on calcareous soil microbial community during days 5,22 and 50 of incubation compared with treatment without DEHP.Two dosage of DEHP(10 and 100mg/kg-1),constantly decreased microbial biomass carbon(MBC)and microbial biomass nitrogen(MBN)concentration.Modified Fenton’s oxidation reaction significantly decreased the inhibitory action of DEHP on soil microbial biomass compared to control(containing only citric acid).At the peak of emission,DEHP(100mg/kg1 only)decreased CO2 emission 44.9% compared to control.CHF(Fe SO4),CHCO(Na3S2O3)and CHCOF(Fe SO4 + Na3S2O3)increased CO2 emission by 12%,69.8% and 75.3% respectively.Although DEHP have detrimental effects on soil nitrogen cycle,soil CO2 emission,they can be biodegraded in the presence of urea and their biodegradation process can be greatly enhanced by Modified Fenton’s chemical oxidation reaction.Prior to this research,there wasn’t enough information to clearly understand all mechanisms related to the effect of DEHP contamination on soil biological properties and DEHP mitigation.This study will provide theoretical reference for future researchers to understand DEHP dynamics variation on soil biological functions and scientific support for building a remediation technology for mitigating DEHP through Chemical oxidation and biodegradation.