新农药哌虫啶在三种典型土壤中的吸附与淋溶研究

摘要

应用振荡平衡法和柱淋洗法研究了哌虫啶在红壤、棕壤和黑土3种典型土壤中的吸附和淋溶特性，并探讨了3种土壤改良剂对其淋溶的影响。结果表明：哌虫啶在黑土、红壤和棕壤中的吸附平衡时间分别为12、12和9 h，分配系数Kd分别为23.16、11.24和4.68，吸附常数Kf分别为22.03、11.69和5.05，KOC值分别为1619、2094和495，吸附自由能值分别为-16.96、-17.59和-14.02 kJ mol-1， Freundlich和线性等温吸附模型均能较好地描述哌虫啶在土壤中的吸附过程，其吸附能力顺序分别为黑龙江黑土＞福建红壤＞山东棕壤。哌虫啶在3种供试土壤中淋溶性存在差异，在棕壤中迁移性最强，随着施药量的增加，其淋出率也略有提高，但3个不同水平施药量差异不显著。在黑土中迁移性最弱，红壤和黑土中的哌虫啶残留量随着土壤深度的增加逐渐降低。土壤中添加0.5%的活性炭、腐殖酸和草炭能显著地降低农药哌虫啶在土壤中的淋溶性，减少对地下水的污染风险。%Objecivet]Paichongding,a neonicotinoid type of insecticide recently developed in China,is easily absorbed by plant and transferred inside the plant. Now it is used mainly for controlling insects of homoptera and expected to have a bright future as a promising new pesticide. Once pesticides enter into the soil,they readily get adsorbed,desorbed and leached in the soil. Their sorption and desorption are the main factors influencing fate of the pesticides in the soil,and seriously affecting their behaviors,like chemical and microbial degradation,volatilization and leaching,and moreover,it is an important index in pesticide environmental safety assessment. The study on its adsorption and leaching characteristics is of important significance to prediction of its environmental behavior and pollution in the soil. [Method]In order to provide a scientific basis for the study of environmental behavior,migration and transformation, of paichongding in the soil,the batch oscillating equilibration method and column leaching method were adopted to explore adsorption and leaching characteristics of paichongding in three typical soils,that is brown soil from Tai’an,red soil from Fujian and black soil from Northeast China,and effects of three soil amendments on leaching of the substance in the soils. Residue of the pesticide in the soil was determined with SPE-HPLC. As in the leachate,the concentration of paichongding was low,the solution underwent concentration and purification with SPE before determination of residue of paichongding in the leachate with HPLC. [Result]Results show that the adsorption equilibrium time of paichongding was 12 h,9 h and 12 h in the red soil,brown soil and black soil,respectively,by absorption dynamics. The Freundlich model and the Linear isothermal adsorption model can well be used to describe the adsorption processes of paichongding in soil. Of the pesticide,distribution coefficient,Kd,was 23.16,11.24 and 4.68,and adsorption constant was 22.03,11.69 and 5.05 in the black soil,red soil and brown soil,respectively. Among the three soils, black soil was the highest in paichongding adsorption capacity and brown soil was the lowest. The adsorption isotherms of paichongding in three different soils fitted fairly the Freundlich model and Linear model at 25℃,with Koc being 1 619,2 094 and 495,respectively,and the absolute values of free energy in all the three soils were less than 40 kJ mol-1,so the adsorption of paichongding in these soils belonged to physical adsorption. Leaching of paichongding varied in the three soils. In the brown soil,paichongding migration rate was the highest,and slightly increased with rising dosage of the pesticide,and the variation with dosage was not significant;In the red soil and black soil,dosage did not have much effect on leaching rate of the pesticide,either,and Only a slight difference in leaching rate was found in the red soil between treatments applied with 200 μg and 500 μg of paichongding. One-way ANOVA analysis of the black soil shows that the effect of dosage was not significant. In the leachate from the brown soil,red soil and black soil,paichongding residue accounted for 16.69%~16.86%,11.55%~13.52% and 8.98%~9.35% of the total applied, respectively. As the black soil was the highest in adsorption capacity,pesticide in the soil was the lowest in mobility. Residue of paichongding in the red soil and black soil decreased with soil depth,but by a little margin. Once activated carbon was added into the soils,it reduced not only migration and leaching rate of paichongding significantly,but also extractable residue by 34.8%,36.79% and 16.93%,respectively,in the brown soil,red soil and black soil;No residue was detected in the leachates from the red soil and black soil,while 76.4% less residue was found in the leachate from the brown soil in the treatments amended with activated carbon. The addition of 0.5% humic acid and peat,separately,reduced the leaching rate of the pesticide by 25.1% and 17.1%,respectively,in the brown soil,by 29.7%% and 23.3%,respectively, in the red soil,and by 42.1% and 27.6 %,respectively,in the black soil. [Conclusion] In brief,the amendment of 0.5% activated carbon,humic acid and peat into the paichongding-contaminated soils can significantly reduce leaching rate of the substance,and hence its risk of polluting the groundwater.