E X T O X N E T
Extension Toxicology Network
A Pesticide Information Project of Cooperative Extension Offices of
Cornell University, Michigan State University, Oregon State University, and
University of California at Davis. Major support and funding was provided
by the USDA/Extension Service/National Agricultural Pesticide Impact
Publication Date: 9/93
TRADE OR OTHER NAMES
Product names include Ally, Allie, Gropper, and Escort.
Metsulfuron-methyl is classified by EPA in acute Toxicity Category III,
and must bear the signal word "Caution" on commercial products (1). There are
tolerances for residues of metsulfuron-methyl in or on raw commodities ranging
from 0.05 ppm for sugar cane and milk, to 20.0 ppm for barley hay.
Metsulfuron-methyl is a residual sulfonylurea compound used as a
selective pre- and postemergence herbicide for broadleaf weeds and some annual
grasses. It is a systemic compound with foliar and soil activity, and it works
rapidly after it is taken up by the plant. Its mode of action is by inhibiting
cell division in the shoots and roots of the plant, and it is biologically
active at low use rates. The most common uses of metsulfuron-methyl include
wheat, barley, rye, and pastures. It can be used with other foliar
herbicides, and is typically applied on cereals at 0.004 - 0.007 pounds active
ingredient/acre, and on non-crop areas at 0.005-0.160 pounds active
ingredient/acre. It is commercially available in the form of dry flowable
formulations. Because it has residual activity in soils, it is necessary to
allow ample time for the chemical to break down before planting certain crops
(22 months for sunflowers, flax, corn, or safflower, and 10 months before
planting sorghum). It should not be used on ryegrass or on pastures
containing alfalfa or clovers (2).
This chemical has very low toxicity in mammals. Based on laboratory
tests, the oral dose of metsulfuron-methyl that causes mortality in half of
the test animals (LD50) is > 5,000 mg/kg in rats. It has low dermal toxicity
in tests with rabbits, with an LD50 > 2,000 mg/kg, and low inhalation toxicity
in rats, with a median lethal concentration in air of greater than 5 mg/liter
air. Moderate but reversible eye irritation has been seen in rabbits, and
mild skin irritation has been observed in guinea pigs. No skin sensitization
has been observed in guinea pigs (3).
Signs and Symptoms of Poisoning
Systemic poisoning by sulfonylurea based compounds is unlikely, unless
large quantities have been ingested. No accounts of poisoning by metsulfuron-
methyl are currently available. (4).
A 2-year feeding study in rats resulted in a No Observable Effects Level
(NOEL) of 25.0 mg/kg/day (or 500 ppm in feed), based on decreased body weights
seen at 250 mg/kg/day (5,000 ppm) which was the highest dose tested. EPA has
based its reference dose (0.25 mg/kg/day) on this study (5).
Multigeneration studies in rats did not result in any reproductive
effects at the highest doses tested of 250 mg/kg/day (5).
Metsulfuron-methyl did not cause developmental abnormalities to offspring
of rats and rabbits fed 1000 mg/kg/day and 700 mg/kg/day respectively during
gestation. These doses represent the highest dose tested for each experiment
The weight of evidence presented by a battery of tests to measure
mutagenicity and other adverse effects on DNA indicates that metsulfuron-
methyl is neither mutagenic nor genotoxic (6).
Negative for rats and mice in laboratory tests, but studies may not have
been at maximum tolerated dose (6).
Metsulfuron-methyl is a moderate eye irritant (6).
Fate in Humans and Other Animals
The chemical is broken down quickly and eliminated from the body. In
tests with radiolabeled metsulfuron-methyl in rats, the excretion half-lives
ranged from 9 to 16 hours and 23 to 29 hours for rats administered low and
high doses, respectively. It did not bioaccumulate in fish (6).
Effects on Birds
Metsulfuron-methyl has very low avian toxicity. The oral LD50 value for
mallard ducks is greater than 2510 mg/kg, and dietary LC50 values for mallard
ducks and bobwhite quail are greater than 5620 ppm (6).
Effects on Aquatic Organisms
The chemical has very low toxicity to aquatic organisms. 96-hour LC50
values are greater than 150 mg/l in rainbow trout and bluegill. Forty-eight
hour toxicity tests with the freshwater invertebrate Daphnia magna resulted in
a LC50 of greater than 150 mg/l (6). A 21-day life-cycle test with Daphnia
magna also exhibited very low toxicity. The NOEL for survival and reproduction
was >150 mg/l.
Effects on Other Animals (Nontarget species)
Metsulfuron-methyl has low acute toxicity to honey bees with a topical
LD50 of greater than 25 ug/bee (6). The LC50 for earthworms is greater than
1,000 mg/kg soil.
Breakdown of Chemical in Soil and Groundwater
The breakdown of metsulfuron-methyl in soils is largely dependant on soil
temperature, moisture content, and pH. The chemical will degrade faster under
acidic conditions, and in soils with higher moisture content and higher
temperature (7). The chemical has a higher mobility potential in alkaline
soils than in acidic soils, as it is more soluble under alkaline conditions.
Metsulfuron-methyl is stable to photolysis, but will break down in ultraviolet
light. Half-life estimates for metsulfuron-methyl in soil are wide ranging
from 14 - 180 days, with an overall average of reported values of 30 days (8).
Reported half-life values (in days) for soil include: clay - 178 (7); sandy
loam - 102 (7); clay loam - 70 (7), 14-28 (8), 14-105 (8); silty loam - 120-
Breakdown of Chemical in Surface Water
The dissipation time for metsulfuron-methyl was investigated in a mixed
wood/boreal forest lake. The DT50 or length of time required for half of the
material to dissipate in water was >84 days when high concentrations of
metsulfuron-methyl were applied, and 29.1 days at concentrations that might be
expected if the chemical is applied for forestry uses (9). The chemical is
stable to hydrolysis at neutral and alkaline pHs, and has a half-life of 3
weeks at pH 5.0, 25 degrees C and >30 days at 15 degrees C (10).
Breakdown of Chemical in Vegetation
Metsulfuron-methyl is rapidly taken up by plants at the roots and on
foliage. The chemical is translocated throughout the plant, but is not
persistent. It is broken down to non-herbicidal products in tolerant plants
Methods for the detection of metsulfuron-methyl exist for soil and water.
Liquid chromatography/mass spectroscopy and bioassay methods are used for
soils, and gas chromatography/electron capture detection is used for
measuring trace levels of the chemical in water (11).
PHYSICAL PROPERTIES AND GUIDELINES
|RfD: ||0.25 mg/kg/day
|NOEL: ||25.00 mg/kg/day (500 ppm) (2 year rat feeding study)
|LEL: ||250.00 mg/kg/day (5,000 ppm) (2 year rat feeding study)
|CAS #: ||74223-64-6
|Molecular Formula: ||C14H15N5O6S
|Chemical Names: ||Methyl 2-[[[[(4-methoxy-6-methyl-1,3,5-triazin-2-yl)amino]carbonyl]amino]sulfonyl]benzoate (CA)
Methyl 2-[3-(4-methoxy-6-methyl-1,3,5-triazin-2-yl)ureidosulphonyl]benzoate (IUPAC)
|Molecular Weight: ||381.4
|Form: ||faint, sweet ester-like white to pale yellow solid
|Melting Point: ||158 degrees C
|Vapor Pressure: ||2.5 X 10 to the minus 12 mm Hg @ 25 degrees C
|Solubility: ||Acetone @ 20 degrees C 36,000 mg/l;
n-Hexane @ 20 degrees C 0.79 mg/l;
Methanol @ 20 degrees C 7,300 mg/l;
Methylene chloride @ 20 degrees C 121,000 mg/l;
Water @ 25 degrees C, pH 4.6 270 mg/l;
Water @ 25 degrees C, pH 5.4 1,750 mg/l;
Water @ 25 degrees C, pH 7.0 2,790 mg/l;
Water @ 25 degrees C, pH 9.0 213,000 mg/l
|pKa: ||3.3 in water @ 25 degrees C
|Kd: ||1.4 (Flanagan silt loam, pH 6.5, 4.02% organic matter)
DuPont Agricultural Products
Barley Mill Plaza
P. O. Box 80038
Wilmington, DE 19880-0402
Review by Basic Manufacturer
Comments solicited: May, 1995
Comments received: October, 1995
Meister, R.T. (ed.). 1996. Farm Chemicals Handbook '96. Meister
Publishing Company. Willoughby, OH.
Thomson, W.T. 1993. Agricultural Chemicals Book II. Herbicides.
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Kidd, H. and D. James (eds.). 1994. Agrochemicals Handbook. Third
edition. Royal Society of Chemistry. Cambridge, England.
Morgan, D. P. (ed.). 1989. Recognition and Management of Pesticide
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Protection Agency. Washington, DC.
U.S. Environmental Protection Agency. 1986. Pesticide Fact Sheet
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Smith, A.E. 1986. Persistence of the Herbicides [14C] Chlorsulfuron
and [14C] Metsulfuron-methyl in Prairie Soils Under Laboratory Conditions.
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Wauchope, R.D., T.M. Butler, A.G. Hornsby, P.W.M. Augustijn-Beckers and
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Toxicology. Springer-Verlag Publishers. NY.
Thompson, D.G., L.M. MacDonald and B. Staznik. 1992. Persistence of
Hexazinone and Metsulfuron-methyl in a Mixed-Wood/Boreal Forest Lake. J.
Agric. Food Chem. 40: 1444-1449.
U.S. Environmental Protection Agency. 1989. Pesticide Environmental
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Division. Washington, DC.
Thompson, D.G. and L.M. MacDonald. 1992. Trace-Level Quantitation of
Sulfonylurea Herbicides in Natural Water. Journal of AOAC International.