The Adsorption/Desorption Properties And Influencing Factors Of Sulfadiazine In Typical Soils

Sulfadiazine(SDZ)is a veterinary drug widely used in livestock and poultry farming in China,causing extensive pollution and environmental risks to the soil.As major agricultural production provinces,Liaoning,Henan,and Sichuan are important distribution areas for typical soils such as black soil,loess and purple soil,where veterinary antibiotics are widely used.In this study,the adsorption-desorption characteristics of SDZ in the soils at different temperatures were investigated by using OECD guideline 106 batch equilibrium adsorption method of black soil,loess,and purple soil as subjects.The effect of environmental variables such as temperature and various physical and chemical properties of soil(p H,SOC,CEC,Clay etc.)on the adsorption-desorption behavior was further explained by the Redundancy Analysis(RDA)method.It is of great theoretical and practical significance to soil environmental risk assessment and pollution prevention.The main findings were as follows.(1)The sorption behavior of SDZ on the three test soils was investigated:The Linear equation was the best fit(R~2=0.982,P<0.01),followed by the Freundlich equation(R~2=0.971,P<0.01)and the D-R equation was a poor fit(R~2=0.895,P<0.01)for the SDZ sorption process.However,the D-R equation was more suitable for the loess.The specific surface area(SSA)and pore volume of the west Henan loess were significantly higher than those of the purple loess and black loess,and the porous nature of the west Henan loess may have an important influence on the SDZ adsorption process.The order of SDZ adsorption in soils was as follows roughly:the black soil>the loess≈the purple soil in the range of 288.15K～308.15 K.The adsorption of SDZ on the test soil proceeded spontaneously and was a heat absorption reaction,which was physical adsorption.(2)The desorption behavior of SDZ on the three test soils was investigated:The residual amount of SDZ was higher in the black soil than in the loess and the purple soil at the same temperature.In the lower temperature range(288.15 K～298.15 K),warming would inhibit the desorption of SDZ in the three soils.Once the temperature exceeds a certain range,the desorption of SDZ in the soil would be promoted.HI(the black soil)<HI(the purple soil)<HI(the loess),The hysteresis of SDZ desorption in black soil was obvious.The highest sorption coefficient of SDZ on black soil among the three test soils and the strong desorption hysteresis in black soil are likely to lead to the long-term accumulation of SDZ in black soil,which is potentially more harmful to the black soil environment.(3)The RDA method was used to study the influence of several soil environmental factors on sorption-desorption behavior,and the results showed that the importance of soil environmental factors on soil adsorption-desorption SDZ characteristics was ranked among SOC≈p H>SSA>CEC>Clay>T.The effect of other index factors except for temperature on soil adsorption-desorption SDZ was at a highly significant level(P<0.01)with the variance explained by 42.9%,42.0%,36.3%,34.4%,and 31.4%.SOC and p H were the key factors that showed differences in the sorption-desorption behavior of SDZ on different soils.The black soil was an acidic sandy loam,while the SOC of the black soil was significantly higher than loess and purple soil,with SOC of 30.950±0.495 g/kg.The p H and SOC content of black soil were the main factors affecting its adsorption capacity of SDZ significantly higher than the other two.The main mechanism of SDZ on black soil was likely to be dominated by cation exchange.The electrostatic repulsion was enhanced between soil particles and SDZ during the adsorption of SDZ by the loess.It was speculated that the adsorption of SDZ on the purple soil was mainly due to the hydrophobicity distribution principle caused by the high energy consumption of cavity coupling.