Persistence and leachability of glufosinate-ammonium in a northern Ontario terrestrial environment

The degradation and leaching potential of the herbicide [C-14]glufosinate-ammonium [the ammonium salt of DL-homoalanin-4-yl(methyl)phosphinic acid] in a northern Ontario forest environment were examined. The DT50 and maximum leaching depth were 4.3 days and 10 cm (humic layer), respectively. [C-14]MPPA-3 (3-methylphosphinylpropionic acid) and [C-14]MPAA-2 (2-methylphosphinylacetic acid), the two main metabolites of glufosinate-ammonium, also did not leach beyond 10 cm. At 32 days postapplication, approximately 10-20% of the parent and metabolites remained in the soil, but by the following season (day 295) residue levels had declined to near zero.