Adsorption, Mobility, and Microbial Degradation of Glyphosate in the Soil

Glyphosate [N-(phosphonomethyl)glycine] was readily bound to kaolinite, illite, and bentonite clay and to charcoal and muck but not to ethyl cellulose. Fe +++ and Al +++ -saturated clays and organic matter adsorbed more glyphosate than Na + or Ca + -saturated clays and organic matter. Glyphosate appears to be bound to the soil through the phosphonic acid moiety as phosphate in the soil competed with 14 C-glyphosate for adsorption sites. Glyphosate mobility in the soil was very limited and was affected by pH, phosphate level, and soil type. The 14 C-glyphosate was biodegraded in soil to 14 CO 2 possibly by co-metabolism. Potentiometric titrations of the compound gave pKa values of 2, 2.6, 5.6, and 10.6.