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Pesticide Mobility in Soils I. Parameters of Thin-Layer Chromatography¹

ABSTRACT

Pesticide movement was studied using the recently developed soil thin-layer chromatographic (TLC) method (Science 162:562, 1968). Thin layers of soil, the adsorbent phase, are developed with water using techniques analogous to conventional TLC.

Mobility, expressed as R_F values for frontal movement, was insensitive to these parameters: removal of coarse or medium sand, movement distance, soil layer thickness, temperature, and sample size (0.3 to 50 µg). Water flux was modified by physical, soil amendment (inorganic and organic additives), and solvent amendment methods. Increased flux may slightly increase mobility of pesticides. The mobilities of 2,4-D and atrazine decreased markedly in > 0.5M NaCl solution, whereas some movement of paraquat then occurred. Distance to the wetting front on soil TLC plates was linearly related to the square root of time.

Three methods of visualizing radioactive pesticide movement were compared: autoradiography, radiochromatogram scanning, and zonal extraction.

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 Div., ARS, USDA, Beltsville, Md. 20705.

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