Glyphosate supplementary information.pdf

Supplementary Information:
Comparison  of  ecotoxicology  and  environmental
fate  of  metsulfuron  methyl,  haloxyfop-R-methyl,
imazapyr isopropylamine and triclopyr TEA with
glyphosate

In New Zealand, the herbicide glyphosate isopropylamine is registered for use in situations
where contamination of aquatic environments may occur and is currently used to control a
wide range of wetland and emergent aquatic weeds. Unfortunately, this herbicide does not
give effective control of a range of problem weed species targeted for eradication including
alligator weed, Manchurian wild rice, phragmites, purple loosestrife, sagittaria, Senegal tea
and spartina. The major drive for seeking permission for the restricted use of metsulfuron
methyl, haloxyfop methyl, imazapyr isopropylamine and triclopyr TEA is to allow for effective
management of these species in eradication programmes.
This paper summarises data on ecotoxicology and environmental fate of glyphosate
isopropylamine as a comparison with herbicides that contain metsulfuron methyl, haloxyfop
methyl, imazapyr isopropylamine and triclopyr TEA, as evaluated in Champion (2012).
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Glyphosate isopropylamine
A range of products with the active ingredient glyphosate isopropylamine are registered to
be used in situations where contamination of aquatic environments may occur in New
Zealand. In most instances, the use of this herbicide in these environments is not subject to
resource consent requirements.
Twenty three products with 360 g/L a.i. glyphosate isopropylamine as a soluble concentrate
are currently available under various trade names, with all but one product recommended for
use in aquatic areas (New Zealand Novachem Manual 2012). There are additional products
with 450, 510 and 540 g/L a.i. (6, 5 and 3 products respectively) (New Zealand Novachem
Manual 2012). Only 540 g/L a.i. formulations recommend “avoid unintentional contamination
of aquatic environments” (New Zealand Novachem Manual 2012).
1.1  Toxicology
The label for all formulations of glyphosate isopropylamine states that those products are
ecotoxic, being toxic to aquatic organisms with long lasting effects (New Zealand Novachem
Manual 2012).
At the rates recommended for application to aquatic plant pests (willow, floating and reed
sweet grasses, Mercer grass, cutty grass and rushes) the maximum concentration of
glyphosate isopropylamine in the spray mix applied to plants would be 8.1 g/L (or mg/kg)
based on a rate of 9 L of the 360g/L a.i. applied per hectare.
The following literature has been used to generate the summary below: Peterson et al.
(1994); EXTOXNET (1996);   Monheit (2002); Solomon & Thompson (2003); Tsui & Chu

(2003) and factsheets from European Glyphosate Environmental Information Source
(EGEIS) and National Pesticide Information Center (NPIS).
Mammalian toxicity
Very low toxicity
Acute oral toxicity that causes mortality (Lethal Dose) in half of the test animals (rats) (LD50)
>5000 mg/kg.
Glyphosate is poorly absorbed from the digestive tract and is largely excreted unchanged by
mammals.
Avian toxicity
Very low toxicity
Acute oral toxicity - mallard (LD50) > 5000 mg/kg.
Aquatic animal toxicity
Very low toxicity
96-hour (Lethal Concentration) LC50 – rainbow trout and bluegill sunfish  180 mg/L.
48-hour LC50 – Daphnia magna (cladoceran crustacean) 930 mg/L.
Solomon & Thompson (2003) concluded that the ecological risk assessment for aquatic
organisms from the application of glyphosate over water at rates less than 4 kg/ha (rate used
in New Zealand is 3.24 kg/ha) is of negligible or low risk.
Non-target aquatic plant toxicity
Very toxic
Glyphosate isopropylamine is less selective than any of the four herbicides assessed by
Champion (2012).  It is currently used to control a range of emergent (plants with foliage
above the water level) plants e.g., willow, floating and reed sweet grasses, Mercer grass,
cutty grass (Carex spp.) and rushes (New Zealand Novachem Manual 2012).
Peterson et al. (1994) showed no observable toxic effect of glyphosate in field trials on the
floating Lemna minor at expected environmental concentrations resulting from herbicide
application. EGEIS report a 1.5 mg/L LC50 for this species.

Algae
Selectively very toxic
Ecotoxicology studies using a range of algal species have found toxicity ranging from
moderate to highly toxic (Peterson et al. (1994); Tsui & Chu (2003)).
Tsui & Chu (2003) found the green alga Pseudokirchneriella subcapitata was the least
sensitive of species tested with an IC50 (inhibition coefficient) of 41 mg/L of glyphosate
isopropylamine. The diatom Skeletonema costatum was more sensitive with an IC50 of 5.89
mg/L. This sensitivity of diatoms to glyphosate was also reported by Peterson et al. (1994)

with a 73 to 77% reduction at expected environmental concentrations resulting from
herbicide application, whereas green algae were reduced by 3 to 18% under the same
concentration.
1.2  Persistence in aquatic habitats
EXTOXNET (1996) report half-life of glyphosate in pond water from 12 to 70 days.  Peterson
et al. (1994) report a half-life of 47 days in their study. Glyphosate is very rapidly adsorbed
by organic or mineral suspended solids and degradation is by microbial activity.
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Comparison with metsulfuron methyl, haloxyfop-R-
methyl, imazapyr isopropylamine and triclopyr TEA

The tables below summarise the persistence of these herbicides in aquatic environments
and toxicity to non-target aquatic organisms:

Table 1.  Chemical persistence in aquatic environments.

Half-life
Breakdown
Agrichemcial
Notes
(days)
method
Haloxyfop-R-methyl
5 – 33
Hydrolysis
Half-life dependant on pH of water.  5
days @ pH 7, several hours @ pH 9.
Imazapyr
2.5 – 5.3
Photolysis

isopropylamine
Metsulfuron methyl
5 – > 90
Hydrolysis
Half-life dependant on water pH and
under acid
initial chemical concentration.
conditions
Triclopyr
0.5 – 7.5
Photolysis

triethylamine
Glyphosate
12 – 70
Metabolised by
Strongly adsorbed to suspended
isopropylamine
microorganisms  organic and mineral matter.

Table 2.  Toxicity of chemicals on selected aquatic species.

Glyphosate
Haloxyfop-R-
Metsulfuron
Imazapyr  Triclopyr
isopropylamine
methyl
methyl
propylamine  triethylamine
Application Rate
(mg/L)
810
750
150
250
792
Rats LD50
>5000
393
>5000
>5000
2574
Mallard LD50
>4500
>5000
>5000
>5000
10000
Rainbow Trout LC50
180
>800
>150
>800
552
Fathead Minnow
LC50
97
1000
-
-
101-120
Bluegill Sunfish
LC50
180
548
>150
>1000
552
Daphnia LC50
930
96.4
150
614
110
Green alga
Pseudokirchneriella
subcapitata IC50
5.56
24.7
1.08
11.5
10.6
Most toxic to
Possibly very
Most toxic to
Moderately
Other algae
diatoms
toxic
cyanobacteria
Low toxicity
toxic
Some selectivity –
grasses, sedges
Selectivity of plant
and rushes
control
Non-selective
Grasses only
tolerant
Non-selective
Dicot selective

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Summary
•  Glyphosate isopropylamine has a longer half-life than haloxyfop methyl, imazapyr
isopropylamine and triclopyr TEA. Metsulfuron methyl is stable under neutral or
alkaline conditions, but breaks down rapidly under acid conditions.
•  Glyphosate isopropylamine is applied at similar concentrations to haloxyfop methyl,
and triclopyr TEA, but higher than metsulfuron methyl and imazapyr isopropylamine
•  Glyphosate isopropylamine has similar mammalian and avian toxicity to metsulfuron
methyl, imazapyr isopropylamine and triclopyr TEA. Haloxyfop methyl is more toxic to
mammals.
•  Glyphosate isopropylamine has similar or higher fish toxicity than metsulfuron methyl,
haloxyfop methyl, imazapyr isopropylamine and triclopyr TEA.
•  Glyphosate isopropylamine is less toxic to Daphnia than metsulfuron methyl,
haloxyfop methyl, imazapyr isopropylamine and triclopyr TEA.

•  Glyphosate isopropylamine has higher toxicity to the green alga Pseudokirchneriella
subcapitata than metsulfuron methyl, imazapyr isopropylamine and triclopyr TEA, but
less than haloxyfop methyl.
•  Glyphosate isopropylamine has less selectivity to non-target angiosperms than
metsulfuron methyl, haloxyfop methyl and triclopyr TEA, but similar to imazapyr
isopropylamine.
•  Glyphosate isopropylamine does not adequately control alligator weed, Manchurian
wild rice, phragmites, purple loosestrife, sagittaria, Senegal tea and spartina.

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Acknowledgements
Leon Keefer and Angus McKenzie (Latitude Planning Services Ltd.) assisted with the
sourcing of information.
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References
Champion, P.D. (2012). Review of ecotoxicology and environmental fate of four
herbicides used to control aquatic weeds. NIWA Client Report HAM2012-049,
Hamilton. 23 pp.
European Glyphosate Environmental Information Source (EGEIS). Aquatic
ecotoxicity of glyphosate and formulated products containing glyphosate.
(http://www.egeis.org/cd-info/Aquatic-ecotoxicity-of-glyphosate-and-formulated-
products-containing-glyphosate.pdf)
E X T O X N E T (Extension Toxicology Network) (1996). Pesticide Information
Profiles: Glyphosate. (http://extoxnet.orst.edu/pips/glyphosa.htm)
Monheit, S. (2002). Glyphosate-based aquatic herbicides: An overview of risk.
Noxious Times 6: 1-10.
National Pesticide Information Center (NPIS). Glyphosate Technical Factsheet
(http://npic.orst.edu/factsheets/glyphotech.pdf)
Peterson, H.G.; Boutin, C.; Martin, P.A.; Freemark, K.E.; Ruecker, N.J.; Moody,
M.J. (1994). Aquatic phyto-toxicity of 23 pesticides applied at expected
environmental concentrations. Aquatic Toxicology 28: 275–292.
Solomon, K.R.; Thompson, D.G. (2003). Ecological risk assessment for aquatic
organisms from over-water uses of glyphosate. Journal of Toxicology and
Environmental Health 6: 289–324.
Tsui, M.T.K.; Chu, L.M. (2003). Aquatic toxicity of glyphosate-based formulations:
comparison between different organisms and the effects of environmental
factors. Chemosphere 52: 1189-1197.