EXTRACTION OF [C-14] GLYPHOSATE FROM SASKATCHEWAN SOILS

The extraction of C-14 from air-dried samples of three soils fortified 14 days previously with [C-14]-glyphosate was compared using 10 different solvent systems and an extended-shaking procedure. C-14 recoveries exceeding 73% were reproducibly achieved with 0.35 M H3PO4 (and 0.09 M with respect to CaCl2), 0.1 M NaOH, and 0.5 M NH4OH. With the phosphoric acid and ammonium hydroxide extractants, highest recoveries from a loamy sand were recorded with a soil/solvent ratio of 1:5 or 1:10. With the aqueous sodium hydroxide, highest recoveries were achieved from all soils using a soil/solvent ratio of 1:2.5. Recoveries of C-14 from all three soils, using 0.1 M NaOH, were not significantly different whether fortified 14, 28, or, in the case of a clay, 56 days previously with [C-14]glyphosate. Some loss of extractable radioactivity was noted in two of the soils after 56 days.