扑草净在不同类型土壤中的吸附-解吸特征研究

Analysis on the Adsorption-desorption Characteristics of Prometryn in Different Types of Soil

【目的】针对土壤中农药的吸附-解吸过程会影响农药在土壤中的迁移、转化和生物利用这一现象,分析了扑草净在我国南方不同类型土壤中的吸附-解吸特征及吸附机理。【方法】吸附试验采用批量平衡法和气相色谱质谱法,研究南方水稻土,红壤和黄壤对扑草净的吸附动力学特性,等温吸附-解吸特征。【结论】(1)扑草净在3种供试土壤中的吸附动力学过程经历了快速(180 min之间)、慢速(180 min之后)及平衡(720 min)吸附3个阶段,这种现象与供试土壤表面吸附位点有限有关。采用不同吸附动力学方程对吸附数据进行拟合,其中准二阶动力学方程与水稻土(R2=0.98)、黄壤(R^(2)=0.97)对扑草净的吸附动力学过程较为吻合,红壤(R^(2)=0.95)对扑草净的吸附动力学用Elovich方程来拟合更适合;(2)扑草净在3种供试土壤的等温吸附均符合Langmuir和Freundlich模型,这表明扑草净在3种供试土壤中的吸附作用主要属于单层吸附,吸附位点均一,是一个以物理作用为主的,自发(ΔG<0)吸附过程,扑草净在3种供试土壤中的吸附能力(Kf值)由大到小依次为:红壤(6.20)、水稻土(4.77)和黄壤(1.10);(3)扑草净在3种供试土壤中的吸附系数Koc为72.74~154.80,吸附较弱,说明扑草净在土壤中的施用对地表、地下水环境等存在潜在污染风险。解吸试验结果表明,扑草净不易从水稻土和红壤中解吸(0.7<HI<1),易从黄壤中(HI>1)中解吸。

[Objective]Because the phenomenon that the adsorption-desorption process of pesticides in soil would affect the migration,transformation and biological utilization of pesticides in soil,the adsorption-desorption characteristics and adsorption mechanism of prometryn widely used in China in different types of soils in southern China were analyzed.[Method]An adsorption experiment was carried out by means of batch equilibrium method and gas chromatography mass spectrometry.The adsorption kinetics characteristics and isothermal adsorption-desorption characteristics of paddy soil,red soil and yellow soil to prometryn were studied[Re⁃sult](1)The adsorption kinetics of prometryn in the three types of soil underwent three stages:fast(the adsorption time was within 180 min),slow(the adsorption time was between 180 min and 720 min)and equilibrium(the adsorption equilibrium was 720 min)adsorption,this phenomenon was related to the limited adsorption sites on the soil surface.The pseudo-second-order kinetic model was in good agreement with the adsorption kinetics of paddy soil(R^(2)=0.98)and yellow soil(R^(2)=0.97)to prometryn,and Elovich model was more suitable for the adsorption kinetics of red soi(R^(2)=0.95)to prometryn(2)The isothermal adsorption desorption of prometryn in the three test soils conformed to the Langmuir and Freundlich equation,which indicated that the adsorption of prometryn in the three tested soils was mainly monolayers and the adsorption sites were uniform.The adsorption of prometryn in red soil,paddy soil and yellow soil was a physically-based phenomenon of the adsorption process.This is a spontaneous(ΔG<0)adsorption process.The experiment result showed that the adsorption capacity(Kf value)of the three test soils to prometryn was in the order:red soil(6.20)>paddy soil(4.77)>yellow soil(1.10).(3)The adsorption coefficient Koc of prometryn in the three tested soils was between 72.74 and 154.80.This indicates that the adsorption of the three tested soils is weak,and there are potential pollution risks to the surface and groundwater environment caused by the application of prometryn in the similar soil environmentand.The desorption experiment results showed that there was hysteresis in the desorption process of pesticides in the three tested soils and prometryn was not easy to desorb in paddy soil and red soil(0.7<HI<1),and easy to desorb in yellow soil(HI>1).In general,in the process of prometryn application,attention should be paid to its amount;or environment-friendly herbicides should be used instead,so as to avoid environmental pollution.