Download Backgrounder Glyphosate and Avian Species Updated

Backgrounder
Glyphosate and Avian Species
Updated November, 2014
Overview
Herbicide formulations containing glyphosate are recognized by private landowners and
governmental agencies as premier control agents for terrestrial and aquatic weeds. Glyphosate
has favorable environmental characteristics, including that it binds tightly to soil, reducing
bioavailability immediately after use, and degrades over time in the environment. Laboratory
and field data indicate little toxicity and low risk to wildlife from direct exposure to glyphosate
and glyphosate herbicides when used according to label directions. The scientific literature
contains hundreds of articles addressing this topic (Sullivan & Sullivan, 2000), including a
section on birds.
Although glyphosate degrades over time in soil and water, the potential for exposure to
glyphosate exists for some avian species, mainly via the consumption of contaminated diet. An
ecotoxicological risk assessment for birds, in which very conservative assumptions were made,
has indicated minimal risk to birds from terrestrial uses of glyphosate herbicides (Giesy et al.,
2000).
The U.S. EPA (1993) and the World Health Organization (1994) have concluded that glyphosate
use according to label directions presents minimal risk of adverse effects to birds. The absence
of direct effects on birds has been confirmed in numerous field investigations reported in the
published literature.
Laboratory Studies
Avian Toxicity Studies
The toxicity of glyphosate to avian species has been investigated in laboratory dietary and oral
toxicity tests using the standard test species: bobwhite quail and mallard duck. Tests have also
been conducted on the original Roundup® herbicide formulation1. The results of these tests are
summarized in Table 1. The dietary tests involved a 5-day exposure in the diet, followed by a 3day observation period; the oral toxicity test used a single oral dose of the test material. These
tests were conducted with juvenile birds 10 to 14 days old. In all but one of the laboratory tests
conducted, there were no treatment-related effects observed at any dose level. These results
qualify glyphosate and the formulation tested to be classified as “practically non-toxic” for acute
avian toxicity.
1
The term “original Roundup herbicide” refers to the original single active ingredient Roundup® herbicide
formulation (also known as MON 2139).
Backgrounder: Glyphosate and Avian Species. 2014.
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Table 1. Dietary and oral toxicity of glyphosate and glyphosate herbicides to avian
species in standard laboratory tests.
Toxicity value: Dietary Studies
(nominal mg/kg in diet)
Species Tested
Acute Dietary Toxicity
Classification (U.S. EPA)
5-day
a
LC50
5-day
a
NOEC
16-17 wk
a
NOEC
Bobwhite quail, Colinus virginianus
>4640
4640
1000
No more than “Slightly
toxic”
Mallard duck, Anas platyrhynchos
>4640
4640
1000
“
--
Practically non-toxic
Practically non-toxic
Practically non-toxic
Glyphosate (tested as acid)
original Roundup® herbicide
1
Bobwhite quail, Colinus virginianus
>5620
3160
b
Mallard duck, Anas platyrhynchos
>5620
5620
--
Zebra finch, Peophilla guttata
>8064
8064
--
Species Tested
Toxicity value: Single-dose Oral
Studies (nominal mg/kg body
weight)
LD50
c
NOEL
Acute Toxicity
Classification (U.S. EPA)
d
Glyphosate (tested as acid)
Bobwhite quail, Colinus virginianus
>3851
1785
e
Practically non-toxic
a
The LC50 is the concentration that produces mortality in 50% of the test animals. The NOEC (no-observed-effect
concentration) is the concentration that produces no effects in the test animals.
b
Effects on body weight and feed consumption observed at the highest dose level (5620 mg/kg diet).
c
The LD50 is the dose that produces mortality in 50% of the test animals.
d
NOAEL: No-observed-effect-level.
e
Only effect observed as transient lethargy on day of dosing.
As indicated above, the no-observed-effect-concentration (NOEC) for the laboratory
reproduction studies was 1000 mg/kg diet in quail and mallard. In those studies, glyphosate
was fed to the test birds at dietary concentrations up to 1000 ppm throughout a one-generation
reproduction study (16-17 weeks). The following reproductive parameters were evaluated: eggs
laid, eggs cracked, eggshell thickness, viable embryos, normal hatchlings, and post-hatching
growth and survival. There were no treatment-related effects on these indicators of
reproductive success at any dose tested. The 1000 ppm NOEC is equivalent to an average
daily intake of 97 and 127 mg/kg body weight in quail and ducks, respectively. In the birds’
environment, long-term exposure would not be expected to exceed 0.41 – 8.1 mg/kg body
weight/day for large and small birds, respectively (Giesy et al., 2000). It is therefore unlikely that
the use of glyphosate herbicides will pose a long-term risk to birds.
Field Studies
There have been no instances reported in the literature of direct toxicity of glyphosate or
glyphosate herbicides to birds following the use of glyphosate herbicides in the field. Several
field studies are available in the published scientific literature in which observations of avian
Backgrounder: Glyphosate and Avian Species. 2014.
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species are reported following the forestry use of glyphosate herbicides (Eggestad et al. 1988;
Santillo et al. 1989b; Freedman 1991; MacKinnon and Freedman 1993; Woodcock et al. 1997;
Lautenschlager et al. 1998). While decreases in bird populations have been observed following
treatment of the habitat with a glyphosate herbicide, these decreases have been attributed to
habitat change resulting from the vegetation removal and subsequent reduction of growth
(MacKinnon and Freedman 1993). After use of a glyphosate herbicide, forest plots were
recolonized by different bird species that favored conifer-dominated stands (Eggestad et al.
1988). The abundance of specific species in areas treated with a glyphosate herbicide is
directly a function of the vegetation present (Lautenschlager et al. 1998). In general, seedeating species prefer glyphosate treated areas because there is a greater abundance of plants
that produce many seeds (Lautenschlager et al. 1998).
The published literature supports the conclusion that habitat changes associated with the use of
glyphosate herbicides can result in both increases and decreases of individual populations.
Other factors that can influence avian populations are the time of year and the species biology.
For example, dabbling ducks that breed in the prairie pothole region will respond positively to a
reduction in cattail populations following the application of a glyphosate herbicide designed for
aquatic use (Solberg and Higgins, 1993).
Exposure Assessment and Risk Characterization
Giesy et al (2000) conducted a conservative exposure assessment for birds. In that
assessment, a hazard quotient (HQ) was derived by comparing toxicity values with predicted
exposures (HQ = toxicity / exposure). This approach is similar to the risk quotient used by the
U.S. EPA for pesticide risk assessment (Urban and Cook 1986). In a first-tier assessment, a
hazard quotient less than or equal to 1.0 indicates minimal risk. However, an HQ value greater
than 1.0 does not suggest that effects would be expected to occur. Instead, this indicates that a
more critical assessment (a second-tier assessment utilizing more realistic exposure
assumptions) should be conducted.
In the Giesy et al. assessment, the acute exposure of birds to the original Roundup® herbicide1
was estimated. The maximum predicted acute exposures for this formulation were predicted to
be 16 mg/kg body weight/day for large birds and 313 mg/kg body weight/day for small birds.
Based on these predicted exposure values, and the laboratory toxicity data, the hazard
quotients were calculated to be 0.03 for large birds and 0.60 for small birds. These values are
well below 1.0, and indicate that there is minimal acute risk to birds from the use of glyphosate
herbicides.
Similarly, the assessment for chronic exposure reported by Giesy et al. indicated long-term
predicted exposures of 0.41 – 8.1 mg/kg body weight/day for large and small birds, respectively.
Based on these exposures and the chronic laboratory toxicity data for glyphosate, hazard
quotients were calculated to be <0.01 to 0.09. These values indicate that there is minimal
chronic risk to birds from the use of glyphosate.
CONCLUSIONS
The results of numerous toxicology studies in various avian species have shown the toxicity of
glyphosate to these species to be very low. Exposure of birds to glyphosate in the environment
is predicted to occur at much lower levels than those that produce toxicity. Therefore, the use of
glyphosate herbicides according to label directions is not expected to pose a significant risk to
birds.
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References
Eggestad ME, Enge E, Hjeljord O, Sahlgaard V. (1988) Glyphosate application in forest ecological aspects. VIII. The effect on Black Grouse (Tetrao tetrix) summer habitat.
Scandinavian Journal of Forest Research 3:129-135.
European Union. (1994) Council Directive 94/43/EC of 27 July 1994 establishing Annex VI to
Directive 91/414/EEC concerning the placing of plant protection products on the market.
Official Journal of the European Communities. No. L 227/31. September 1, 1994.
Giesy JP, Dobson S, Solomon KR. (2000) Ecotoxicological risk assessment for Roundup®
herbicide. Reviews of Environmental Contamination and Toxicology 167: 35-120.
Hoerger F, Kenaga E. (1972) Pesticide residues on plants: Correlation of representative data
as a basis for estimation of their magnitude in the environment. Environmental Quality 1: 928.
Mackinnon DS, Freedman B. (1993) Effects of silvicultural use of the herbicide glyphosate on
breeding birds of regenerating clearcuts in Nova Scotia, Canada. J. Appl. Ecol. 30:395-406.
Santillo DJ, Brown PW, Leslie Jr. DM. (1989) Response of songbirds to glyphosate-induced
habitat changes on clearcuts. J. Wildlife Manage. 53:64-71.
Solberg KL, Higgins KF. (1993) Effects of glyphosate on cattails, invertebrates, and waterfowl
in South Dakota wetlands. Wildl. Soc. Bull. 21:299-307.
Sullivan DS, Sullivan TP (2000) Non-target impacts of the herbicide glyphosate: A
compendium of references and abstracts. 5th Edition. Applied Mammal Research Institute,
Summerland, British Columbia, Canada.
United States Department of Agriculture (USDA). (1989) Vegetation management in the
coastal plain/piedmont. Final Environmental Impact Statement. Management Bulletin R8MB-23.
Urban DJ, Cook NJ. (1986) Hazard Evaluation Division, Standard Evaluation Procedure:
Ecological Risk Assessment. PB86-247657) U.S. Environmental Protection Agency,
Arlington, VA.
U.S. EPA (1993) Reregistration eligibility decision (RED): Glyphosate. Environmental
Protection Agency, Office of Prevention, Pesticides and Toxic Substances, Washington, DC.
URL: http://www.epa.gov/oppsrrd1/REDs/old_reds/glyphosate.pdf
WHO (World Health Organization) (1994) Glyphosate: Environmental health criteria 159.
World Health Organization, Geneva, Switzerland. URL:
http://www.inchem.org/documents/ehc/ehc/ehc159.htm
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