PARENT SESSION
PS19 - Bioavailability
Sunday, 17 November 2002
8:00 AM to 6:30 PM
Exhibit Hall
(P176) Toxicokinetics of glyphosate and 2,4-D butoxyethyl ester in early-life stage Xenopus laevis.
Edginton, Andrea*,1, Stephenson, Gerry1, Boermans, Herman1, 1 Univeristy of Guelph, Guelph, Ontario, Canada
ABSTRACT- Glyphosate and triclopyr, or (and) the closely related herbicide 2,4-D, are currently aerially applied in Canadian forestry for the control of competing vegetation in conifer replanting sites. The formulated glyphosate product Vision contains the isopropyl amine (ipa) salt of glyphosate plus a 15% v/v polyethoxylated amine surfactant. Release, another forestry-used herbicide, contains the butoxyethyl ester (BEE) of triclopyr. Amphibians use small forestry wetlands as breeding and foraging sites and are exposed to these herbicides as a result of direct or off-target deposition. Previous studies demonstrated that these chemicals are most toxic to early larval stages in comparison to embryonic stages, however their toxicokinetic characteristics have not been studied in this sensitive life stage. To characterize the uptake, disposition and elimination of the herbicides in frogs, radiolabeled glyphosate and 2,4-D BEE were used in aquatic exposures of Xenopus laevis Gosner 25 larvae. Organisms were placed in treatments containing the ipa salt of glyphosate with and without the surfactant or 2,4-D BEE at a concentration at least twenty times less than the 96h LC50. At five sample times during the uptake phase, a water and organism sample were taken to determine the concentration of the parent and metabolites in both the water and in the organisms. Five to seven sample times were employed during the elimination phase following removal of organisms to untreated water. Parent compound and metabolite concentrations were determined using HPLC for 2,4-D BEE and its associated acid and GC for glyphosate and its associated metabolite, AMPA. Preliminary results suggest that the 2,4-D BEE is absorbed as the ester and quickly eliminated as the acid, whereas metabolism of glyphosate is minimal. The combination of toxicokinetic modeling and toxicodynamic parameters generated by this study will allow for a better understanding of chemical effects and a more robust analysis of potential adverse effects of these herbicides under operational use.
Key words: herbicides, amphibians, toxicokinetics