Effects Of Dissolved Organic Matter From Cow Manure On The Sorption And Desorption Behavior Of Triazine Pesticides On Loess Soil In Northwest China

Loess is mainly distributed in Gansu,Ningxia,Shaanxi and other northwest regions and North China,of which the Loess Plateau accounts for 72.4%of loess area in China.Loess in the northwest is located in arid and semi-arid alpine areas,which is characterized by low organic matter content,loose soil,and porous.In order to improve the contents of soil organic matter（SOM）,the application of natural organic fertilizer is common agricultural application in the Northwest China.However,with the more and more applications of natural organic fertilizer,the pollution of herbicides,insecticides and chemical with fertilizers has increased in the loess soil in northwest China.Atrazine（ATZ）and prometryn（PRM）with the low cost and broad herbicidal spectrum,are the most widely used products of the triazine pesticides,which are often used in fields where crops such as corn,sugar cane,tea gardens,and sorghum are grown.Both ATZ and PRM can affect fish hormone levels,which can be considered as endocrine disruptors to induce human cancers and congenital diseases.They have"three causes"effect and can interfere with the central nervous system of advanced animals.At present,ATZ and PRM have been detected in soil,surface water,groundwater and other environmental media,and even in crops,milk and other food products.In order to reduce the effects of triazine pesticides such as ATZ and PRM on human health,it is necessary to understand the transfer and transformation behavior of these organic pollutants in soil.Based on the above background,the adsorption/desorption behavior of ATZ and PRM in typical loess in Northwest China was discussed in this study,and the application effect of cow manure and DOM from cow manure on the sorption/desorption behavior of ATZ and PRM to loess in Northwest China were also studied.The results are as follows:（1）Characterization analysis of DOM from cow manure showed as:The element composition of DOM was similar to that of decomposed chicken manure and soil,and the value of（O+C）/N was 31.43,indicating that the polarity of DOM was relatively high.SUVA₂₅₄and SVUA₂₆₀values of DOM were 0.021 and 0.018,respectively,indicating that the hydrophobicity of DOM was less strong.The spectral slope S_Rvalue was 2.848,indicating that DOM was mainly composed of low molecular weight substances.The value of E₂₅₀/E₃₆₅was 2.96,and it was less than 3.5,indicating that humic acid was the main humus in DOM from cow manure.The absorption peaks appeared at 3426 cm^-1,2985 cm^-1,2834 cm^-1,1608cm^-1,1400 cm^-1and 1365 cm^-1in the infrared spectrum,indicating that the DOM from cow manure was mainly composed of-COOH,-C=O,-CHO and other substances with high unsaturation.In the ¹³C NMR spectrum,there were large absorption peaks at 23.93,30.46,30.46,72.62 and 174.85 ppm,indicating that DOM from cow manure contained more functional groups such as-COOH and-CHO,and more proteins and polysaccharides.The results of 3D EEM showed that the fluorescence peak of DOM from cow manure belonged to the peak C E_x/E_m=420/492 nm,and the FI and BIX values were 1.46 and 0.17,respectively.（2）The kinetic sorption of ATZ and PRM showed that the sorption equilibrium time of ATZ and PRM on loess soil was 8 h and 6 h,respectively.The addition of cow manure or DOM from cow manure could prolong the sorption equilibrium time of ATZ to about 16 h,and the sorption equilibrium time of PRM to about 8 h and 12 h,respectively.The sorption kinetics of ATZ and PRM on loess soil was consistent with the pseudo-second-order kinetics model regardless of whether cow manure or DOM was applied,indicating that the kinetic sorption processes of ATZ and PRM on loess soil was complicated.The sorption kinetics of ATZ and PRM on loess soil was controlled by several processes including external liquid film diffusion,intraparticle diffusion and surface sorption.The results showed that the external diffusion was the main rate control step.（3）The thermodynamic sorption results of ATZ and PRM on loess soil showed that low temperature was more conducive to the sorption of ATZ.Regardless of whether cow manure or DOM was applied,the sorption capacity of PRM decreased with the increase of temperature,indicating that the sorption process was an exothermic reaction.Freundlich isothermal model can describe the sorption process of ATZ and PRM on loess soil with 1/n less than 1,which belongs to"L"type sorption,and the sorption process was multi-molecular layer sorption.The HI value of ATZ and PRM in loess soil is less than 0.7,indicating a positive hysteresis.However,the application of DOM improved the desorption capacity of ATZ and PRM,indicating a negative hysteresis with HI greater than 1.The results showed that the application of cow manure or DOM had a obviously effect on the sorption and desorption capacity of ATZ and PRM.（4）The results of influencing factors showed as:under the same initial concentration of ATZ and PRM,the sorption capacity on loess soil was in the order of soil+cow manure group>soil+DOM>soil group.The higher the initial concentration,the more cow manure or DOM was applied,the greater the sorption capacity of ATZ and PRM on loess soil.The p H has a significant effect on the sorption of ATZ and PRM on loess soil.Regardless of whether cow manure or DOM was applied,with the increase of p H,the sorption amount of ATZ by loess soil decreases,and the sorption amount of PRM increases first and then decreases.The addition of cow manure and DOM can enhance the sorption capacity of ATZ and PRM on loess soil.The more the dosage of cow manure and DOM was applied,the more obviously enhance was observed,and the effect of cow manure was more significant than that of DOM.The application of cow manure or DOM would increase the SOM of loess soil and promote the sorption amounts of ATZ and PRM in loess soil,but the application of DOM will promote the desorption ability of ATZ and PRM in loess soil,which enhance the mobility of triazine pesticides in loess soil and increase the risk of triazine pesticides to surface water and groundwater pollution.