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Pesticide Mobility in Soils II. Applications of Soil Thin-Layer Chromatography¹

ABSTRACT

Forty pesticides were grouped into five categories based on relative mobilities on Hagerstown silty clay loam plates, using soil thin-layer chromatography. Diffusion was also examined in moist and air-dry soils. Methyl esterification greatly reduced mobility of herbicides while increasing diffusion and volatility. The surfactant Tween 20 (1% in solution) increased 2,4-D movement, but 0.5% solutions of five surfactants were relatively ineffective with several herbicides. Metabolites of atrazine, propanil, and 2,4-D were less mobile than their parent compounds. Two chlorinated dibenzo-p-dioxins, potential 2,4,5-T impurities, were immobile. Movement of components in chlorpropham/propham/p-chlorophenyl methylcarbamate and atrazine/propachlor combinations were mutually independent.

Dicamba and fenac R_F values were directly related to soil pH in the range of pH 5.0 to 6.5–6.7. Other soil modifications included in situ oxidation of soil organic matter and the use of model clays. Chlorpropham and propham mobilities were increased by removal of organic matter. Diphenamid was less mobile in oxidized soil, immobile in Ca-montmorillonite, and moderately mobile in kaolinite.

¹ Presented in part before Div. S-1 and S-2, Soil Science Society of America, Nov. 13, 1968, at New Orleans, La.

² Research Soil Scientist (Chemist), Plant Science Research Division, ARS, USDA, Beltsville, Md. 20705.

Received for publication February 10, 1971. Accepted for publication May 14, 1971.