Leaching behavior of metolachlor in soil

This work estimated the leaching behavior of metolachlor from montmorillonite-based and commercial emulsifiable concentrate (EC) formulations in soil columns and field plots by using bioassay and chemical techniques. A montmorillonite-based formulation of metolachlor was prepared by adsorbing metolachlor to montmorillonite–benzyltrimethylammonium (BTMA) complex from aqueous solution. Bioassay and gas chromatography (GC) techniques detected high metolachlor concentrations in the top soil layers (0–9 cm) in soil columns and field plots sprayed with montmorillonite–BTMA–metolachlor complex. These results were also evident by severe growth inhibition restricted to the top soil layers (0–9 cm) and normal growth at deeper layers in soil columns and field plots. A wider range of metolachlor concentrations were detected in soil layers in columns treated with EC formulation in both soil columns and field plots. Relatively higher metolachlor concentrations were detected in the soil layers in field plots than in soil columns. A bioassay technique was a more sensitive tool than chemical technique and detected diluted concentration of metolachlor at deeper layers. The different leaching behavior of metolachlor applied as montmorillonite–BTMA complex is due to the adsorption capacity of montmorillonite–BTMA complex. Key words: metolachlor, montmorillonite–BTMA, leaching, soil columns, field plots.