The Fate and Effect of Glyphosate on Amphibians

1. The Fate and Effect of Glyphosate on Amphibians An Ecological Risk Assessment Evan Hallas Kate Johannesen Matt Berg

2. Approach • Review studies on the transport of glyphosate into aquatic ecosystems and its effects on amphibians • Analyze based on location (lab vs. field), methods, and whether or not there was a surfactant in the glyphosate tested. • Examine source and validity of data

3. Why Study Glyphosate? • Argument exists over the toxicity of the substance • Different environmental factors expected to effect toxicity • Necessity for reevaluation of EPA toxicity classification

4. What Is Glyphosate? • World’s top selling herbicide • Released by the Monsanto Company in 1974 (in Roundup) • Use has tripled since 1997

5. How it Works • Inhibits the shikimate enzyme pathway • Distributed with a surfactant • Imitates glycine

6. EPA Toxicity Classification • Glyphosate is currently classified as a Level III toxin, which means that it is only “slightly toxic” • Registration eligibility decision completed 14 years ago • Patent law protects manufacturer from listing “inert” ingredients

7. The Fate of Glyphosate in Wetlands • Unlikely for glyphosate to leach into groundwater due to surfactant • Contamination can occur by drift/overspray and direct application • Actual concentrations observed are dependent on several factors including application rate, interception by target vegetation, water depth, amount of suspended solids, and type of water body.

8. Potential Concentrations (Giesy et. Al., 2000)

9. Studies on Glyphosate • A limited amount of research has been done regarding the impacts of glyphosate on the environment and amphibians • Most experiments have been completed in labs • Experiments revealed that surfactant was the major toxin

10. Roundup® Lab Experiment • Dr. Rick Relyea Tested Effects of Roundup® on six species of larval amphibians • Simulated ecosystems with caged predators • Estimated LC50 values in mg of Active Ingredient (AI)/L for each species using regression analyses (Relyea, 2005a)

11. (Relyea, 2005a)

12. Soil and Roundup® Effects • Tested three different soil treatments: no soil, loam, and sand • Simulated a direct field overspray creating a concentration of 3.8mg AI/L • Examined survival rates of tadpoles for three different species (Reyea, 2005a)

13. Effects of Vision® on Forest Wetlands • Vision® contains a POEA surfactant and was applied at concentrations of .29 – 14.3 mg A.I./L to separate enclosures • Results showed no statistically significant decrease in survival rates of larval amphibians at the levels that could be expected to be found in nature, 1.43 mg A.I./L • 96-hour LC50 ranged from 2.70 – 11.5 mg A.I./L depending on species and site

14. Glyphosate vs. Surfactant • Different formulations of glyphosate tested: glyphosate isopropylamine, Roundup® Herbicide, and Roundup® Bioactive • Those with surfactants are most toxic • Glyphosate isopropylamine toxin levels higher then expected to be found in natural settings

15. (Mann and Bidwell, 1999)

16. Other Factors • University of Guelph study showed elevated toxicity with a higher pH • Potential for ecosystems to decrease exposure to amphibians compared to lab testing • Actual concentrations in natural ecosystems • Recommended use vs. actual use

17. Conclusion • More research is necessary • Glyphosate is only toxic due to its use with a surfactant • Need for change in FIFRA regulations-inert ingredients must be included in risk analysis