Download The Fate and Effect of Glyphosate on Amphibians

The Fate and Effect of
Glyphosate on Amphibians
An Ecological Risk Assessment
Evan Hallas
Kate Johannesen
Matt Berg
Approach
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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
Why Study Glyphosate?
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Argument exists over the toxicity of the
substance
Different environmental factors expected
to effect toxicity
Necessity for reevaluation of EPA toxicity
classification
What Is Glyphosate?
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World’s top selling
herbicide
Released by the
Monsanto Company in
1974 (in Roundup)
Use has tripled since
1997
How it Works
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Inhibits the shikimate
enzyme pathway
Distributed with a
surfactant
Imitates glycine
EPA Toxicity Classification
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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
The Fate of Glyphosate in Wetlands
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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.
Potential Concentrations
(Giesy et. Al., 2000)
Studies on Glyphosate
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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
Roundup® Lab Experiment
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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)
(Relyea, 2005a)
Soil and Roundup® Effects
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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)
Effects of Vision® on Forest
Wetlands
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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
Glyphosate vs. Surfactant
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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
(Mann and Bidwell, 1999)
Other Factors
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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
Conclusion
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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