Adsorption, Mobility, and Persistence of Thiabendazole and Methyl 2-Benzimidazolecarbamate in Soils

Adsorption of thiabendazole (TBZ) and 2-benzimidazolecarbamic acid methyl ester (MBC) to three soils was studied. With increasing acidity of the soil suspensions an increase in the adsorption of these fungicides to the soil occurred. Results indicated ionization of benzimidazole fungicides at lower pH values, and adsorption of these ionized molecules on the soil. Thiabendazole was adsorbed to the soil in much larger quantities than MBC, and therefore at equilibrium TBZ was detected in the free soil solution in much smaller concentrations. The mobility of TBZ in the soil was also much smaller than that of MBC. The persistence of these fungicides in soil samples, incubated at 25° in small glass vials, was also examined. Nine months after adsorption of these fungicides to the soil, 85-95% of the applied TBZ and 65-75% of the applied MBC were recovered from air dried soils. However, in moist soil after 9 months of incubation only 75-90% of the applied TBZ and 20-30% of the applied MBC were recovered.