PARENT SESSION

1J - Bioaccumulation
Poster Hall
8:30 AM - Wednesday, 30 April 2003
Chair: Tarazona, J.¹, ¹
Co-chair: Gobas, F.², ²

(WEP/75) Toxicokinetics of glyphosate in the early-life stage of the amphibian, Xenopus laevis.

Edginton, Andrea ¹, Stephenson, Gerald¹, Rouleau, Claude², Boermans, Herman¹, ¹ University of Guelph, Guelph, Ontario, Canada² National Water Research Institute, Burlington, Ontario, Canada

ABSTRACT- Toxicokinetic parameters quantitatively describe the concentration of chemical in an organism as a function of time and dosing regime. The absorption, distribution and elimination of glyphosate and the effects of food availability, were studied in the African clawed frog, Xenopus laevis. Glyphosate is a widely used herbicide for the control of broadleaf and grass weeds. In forestry situations, aerially applied glyphosate (formulation Vision), can contaminate wetlands used by amphibians as foraging and breeding sites. Gosner stage 25 larvae, a sensitive life stage of amphibians to environmental contaminants, was used a model system. We examined glyphosate toxicokinetics using various techniques: water exposure, injection and whole body autoradiography (WBARG). Whole body burdens were quantified using radiolabeled glyphosate following larval digestion and liquid scintillation counting. Modelling was conducted using whole-body concentrations corrected for growth dilution. For the water exposure, an 8 h uptake phase in water was followed by a 120 h depuration phase. The absorption and elimination of glyphosate was modeled under food limiting and non-limiting conditions. The half-life of elimination of parent glyphosate was 135 h when no food was provided and 73-104 h with food. Injection experiments provided information about elimination while bypassing the absorptive phases of the gastrointestinal tract. The half-life of elimination following injection was between 5-10 h. WBARG was performed to determine the distribution of glyphosate in the larvae following water exposure. Results indicated that 50% of the total body burden of glyphosate from water exposure was located in the gastrointestinal tract. We conclude that the actual rate of branchial elimination is close to the results obtained from injection experiments. However, parameters obtained from water exposures suggest that glyphosate elimination is protracted due to absorptive or adsorptive process in the gut.

Key words: glyphosate, amphibians, toxicokinetics