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Soil Adsorption and Its Mechanism of the Fungicide Mepanipyrim
Yutaro NAGAI, Kayoko SHIMBA, Yoshio YUSA and Akira YAGI
J. Pestic. Sci.
24, 280-286 (1999)
Soil adsorption of mepanipyrim labeled with 14C was investigated using a batch equilibrium method, and isotherms were calculated by the Freundlich equation for five different Japanese soils collected from the upland fields. The Freundlich equation described mepanipyrim adsorption adequately. Adsorption coefficients (Kf) ranged from 12.9 to 427, and normalized Kf based on the soil organic carbon content (Kf,oc) from 1090 to 5210. The values of l/n were smaller than unity for all soils tested. Desorption of mepanipyrim was hysteretic. Soil adsorption of mepanipyrim was pH dependent, showing the maximum adsorption at a pH value in the vicinity of its pKa 2.9. It is considered that the ionic bond between protonated mepanipyrim and the minus charge on soil colloid contributes to this pH effect. After decomposition of the soil organic matter with H2O2, Kf Values decreased for all soils tested. Adsorption of mepanipyrim on the H2O2 treated soils increased with the decreasing pH in the pH range above the pKa value.
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