| Hainan Province is China's most important production base for winter melons and vegetables and for tropical fruits, where infection of plant diseases and insect pests take place in large areas. Frequent use and overdose of pesticides have polluted the fruit, vegetables, grains and the soil in various degrees. Chlorpyrifos, as an efficient, broad spectrum and medium-and-low toxic organophosphorus pesticide, acaricide and nematocide, is widely used in Hainan province. In order to evaluate the migration and absorption characteristics of chlorpyrifos in the soil, this study employs simulated soil column and batch equilibrium method for investigating the leaching migration and absorption-desorption characteristics of chlorpyrifos in several typical soils of Hainan. The results obtained are mainly in the following aspects:(1) The number of chlorpyrifos in the leaching water of7soil columns is quite small, less than0.001%of the total added chlorpyrifos. The total content of chlorpyrifos in each soil column is dependently variable with the total content of leaching water, that is, with the increasing of total leaching water, the content of chlorpyrifos in it increases. The total N content in the soil has negative effect on the content of chlorpyrifos in the leaching water, and the PH value of soil plays the positive role.(2) The result of distribution analysis of chlorpyrifos in soil column shows that their distribution varies with the type of soil. The volume of leaching water has influences on the distribution of chlorpyrifos in soil, that is, as the leaching water increases, the maximum leaching depth of chlorpyrifos and their depth of peak value will vary in an increasing manner.(3) The study on the effect of soil physiochemical property on the migration of chlorpyrifos approves that on the tenth day the total N content and organic content of soil has significantly positive correlation with the content of chlorpyrifos of depth from0to6cm, and the correlation of soil clay particle therewith is extremely positive. On the twentieth day the correlation of content of chlorpyrifos of depth from0to6cm with the soil clay content is significantly negative, which means the content of soil clay particles hinders the migration of chlorpyrifos down to the lower soil, so are the organic content and the total N content.(4) The study on the absorption thermodynamics behavior of chlorpyrifos in different soils shows that through Frundlich equation the fitting absorption data can be well obtained. By comparing the values of constant Kf in the equation, the chlorpyrifos absorption capability of7different soils are obtained as follows:Soil No.4>Soil No.1>Soil No.3>Soil No.6> Soil No.5>Soil No.2>Soil No.7. Meanwhile, desorption experiment shows the same result. Therefore, it can be concluded that the silt particle content in soil plays a leading role in the absorption of chlorpyrifos in soil and that the organic content and total N content are also important factors affecting the said absorption. On the other hand, it is concluded from the desorption experiment that the CEC content in soil is the most significant factor that affects the chlorpyrifos desorption of soil and that the potassium content also plays an important role. |
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