Study On The Sorption And Transformation Of Steroid Estrogens In Purple Soil During Biogas Slurry Irrigation Region

A large amount of steroid estrogens（SEs）are produced by the metabolism of animals in concentrated animal feeding operarions.It is estimated that the SEs from livestock and poultry feeding farms account for 90%of the total emission in the environment.However,the control measures of urine and manure are still not perfect at present.Most biogas slurry by anaerobic digestion is often used for soil irrigation,consequently,SEs can leach into soil environment and waters through rainfall,surface runoff and so on during biogas slurry reclaim region,causing adverse effects on the ecological environment and human health.The purple soil is the most widely distributed soil in southwest China,meanwhile,the sorption,transport and transformation properties of SEs in purple soil are still unclear.The study of SEs’environmental behavior is mostly focused on free estrogens（FEs）while fewer studies pay attention to the behavior of conjugated estrogens（CEs）in soil environment.Therefore,the mechanisms of sorption,transport,and transformation of SEs in purple soil were studied and explored in this project.Four natural SEs including estrone（E1）,17α-estradiol（17α-E2）,17β-estradiol（17β-E2）and estrone-3-sulfate（E1-3S）were studied in this project.The typical purple soil samples were collected in southwest China.The sterilized soil by autoclaving sterilization was applied for studying the sorption,transport and abiotic transformation properties of SEs in purple soil.In addition,the contamination risk in soil-water environment of SEs was evaluated by estimated 17β-estradiol equivalency（EEQ）.The adsorption of SEs on purple soil achieved at adsorption equilibrium after 24 h and can be divided into two stages:quick adsorption and slow equilibrium.The adsorption process of SEs in soil can be well described by the pseudo-second-order kinetic equation.Langmuir and Freundlich isotherm models also fit the experimental data well.The adsorption parameters and adsorption capacity（E1-3S<17α-E2≈17β-E2<E1）of SEs in soil decreased with the increase of temperature.The adsorption of SEs in soil organic carbon（SOC）is dominated by hydrophobic partition.The correlation between organic carbon normalized distribution coefficient(K_oc)and the octanol-water partition coefficient(K_ow)as well as water solubility（S_w）is relatively high.The adsorption process of SEs in purple soil was a spontaneous thermal process and mainly physical adsorption by thermodynamic analysis.The soil samples were analyzed by fourier transform infrared spectroscopy（FTIR）,X-ray diffraction（XRD）and scanning electron microscopy（SEM）before and after SEs adsorption.The results showed that the H-bonding interaction between organic matter and SEs molecules occurred during the adsorption process.The intercrystal spacing of soil minerals decreased after SEs adsorption and the surface of soil particles became relatively smooth.The leaching ability of SEs in soil was in the order of E1-3S>>17β-E2>17α-E2>E1.Several SEs can transform mutually and the stabilization order is as following:E1-3S test>E1 test>17α-E2 test>17β-E2 test.The transformation products SE₂₃₉ and E2₃₇₈were detected frequently according to electron spray ionization（ESI）scanning results in top-and subsoil samples.Besides,the relative intensity of transformation products E1dimer₅₃₈ and E1-E2 dimer₅₃₈ were higher in E1-3S simulated irrigation experiment.The soil-water pollution risk of E1 and 17β-E2 was higher than 17α-E2 and E1-3S by the estimation of EEQ value and principal component analysis.The sorption,transport and transformation properties of SEs in purple soil were studied in this project.In addition,and the EEQ value was evaluated during the transport and transformation process.The theoretical basis is provided for elucidating the transport pathway and contribution of SEs to soil-water environment during biogas slurry irrigation region.