FATE OF GLYPHOSATE IN A CANADIAN FOREST WATERSHED .2. PERSISTENCE IN FOLIAGE AND SOILS

Residues of glyphosate [N-(phosphonomethyl)glycine] and the metabolite (aminomethyl)phosphonic acid (AMPA) were monitored in foliage, leaf litter, and soils following aerial application of ROUNDUP herbicide (nominal rate 2.0 kg/ha AI) to the Carnation Creek watershed of Vancouver Island, British Columbia. Glyphosate deposit was variable, ranging from 1.85 to 2.52 kg/ha AI, depending upon location within the watershed. Foliar residues in red alder and salmonberry were 261.0 and 447.6 μg/ g, respectively, indicating good impingement on the target foliage. Leaf litter residues, which averaged 12.5 μ μ/g for red alder and 19.2 μg/g for salmonberry initially, declined to less than 1 μg/g within 45 days postapplication (DT5014 days). In soils, glyphosate and AMPA residues were retained primarily in the upper organic layers of the profile, with <90% of total glyphosate residue in the 0-15-cm layer. Distribution data for both glyphosate and AMPA suggested strong adsorption and a low propensity for leaching. Glyphosate soil residues dissipated as a function of time with an estimated DT50of 45-60 days. After 360 days, total soil residues of glyphosate were 6-18% of initial levels. © 1990, American Chemical Society. All rights reserved.