|Chemical Abstract Number (CAS #)||
Link to the National Library of Medicine's Hazardous Substances
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on this compound.
|Use|| Preemergence and preplant incorporated weed control in corn, soybeans, peanuts, grain
sorghum, potatoes, pod crops, cotton, safflower, and woody ornamentals.
Control of annual grasses and some broad-leaved weeds in maize, sorghum, cotton,sugar beet,
fodder beet, sugar cane, potatoes, groundnuts, soyabeans, safflowers, sunflowers, some
vegetables, and woody ornamentals. Applied pre-emergence or pre-plant incorporated. Often
used in combination with broad-leaved herbicides, in order to extend the spectrum of activity.
It is a germination inhibitor active mainly on grasses at 1.0-2.5 kg ai/hectare Mixtures with
other herbicides are also used in broad beans, carrots, hemp, lentils, paprika.
Dual 8E is a selective herbicide for control of annual grass weeds, yellow nutsedge (Cyperus
esculentus), and certain broadleaf species . Dual may be used alone or in tank or prepackaged
mixtures with atrazine or propazine for weed control in Concep safened sorghum.
Representative examples of weeds controlled include barnyardgrass (Echinochloa crusgalli),
crabgrass (Digitaria species), fall panicum (Panicum dichotomiflorum), foxtails (Setaria species),
broadleaf signalgrass (Brachiaria platylhylla), goosegrass (Eleusine indica), witchgrass (Panicum
capillare), red rice (Oryza sativa), pigweed (Amaranthus species), carpetweed (Mollugo
verticillata), and Florida pusley (Richardia scabra).
|Apparent Color|| Clear liquid; White to tan liquid
|Boiling Point|| 100 deg C at 0.001 mm Hg
|Molecular Weight|| 283.81
|Density|| 1.12 g/cu cm (20 deg C)
|Sensitivity Data|| Skin eye and mucous membrane irritation.
|Environmental Impact|| Metolachlor is a herbicide used on a number of crops to control annual grasses and many
broad-leaved weeds. The release of metolachlor in the environment occurs during the manufacture
and particularly from its use in the field. In soil, metolachlor is transformed to its metabolites
primarily by biodegradation. The half-life of metolachlor disappearance from soil is about 90 days,
although very little mineralization has been observed. Metolachlor is highly to moderately mobile.
Although a slow process, biodegradation is a major pathway for the loss of metolachlor in water.
The bioconcentration of metolachlor in aquatic organisms is not important. Reaction of
metolachlor with photochemically produced hydroxyl radicals may be the most important loss
process in the atmosphere. The half-life of metolachlor due to this reaction has been estimated to
be 1.8 hrs. Partial removal of metolachlor will also occur as a result of dry and wet deposition.
Metolachlor has been detected in surface water and groundwater around sprayed farmlands. It has
rarely been found in community drinking water. The applicators of the herbicide are the most
likely people for exposure to metolachlor by inhalation and dermal routes.
|Environmental Fate|| TERRESTRIAL FATE: Biodegradation will be the major process by which metolachlor
will be lost from most soils . Although metolachlor degraded in a soil with a half-life of 56 days,
only approximately 5% of the compound mineralized to carbon dioxide in 84 days . Some loss
of metolachlor from soil surface will occur as a result of photolysis by sunlight . Experimental
results confirm that metolachlor absorbs weakly to moderately to soil and the leaching of
metolachlor from soil is high to medium . Volatilization of metolachlor from poorly adsorbing
moist soil to the atmosphere may be significant if assisted by solar heating and high winds .
Depending on the nature of soil and climatic conditions, the field half-life of metolachlor in soil
ranged from 11 to 180 days(1,3) with an average half-life of 90 days .
AQUATIC FATE: Biodegradation is expected to occur slowly based upon soil studies . The
disappearance of metolachlor in groundwater free of aquifer materials (e.g., sand) was very slow
and the half-life was in the range 548-1074 days . When aqueous solution of metolachlor was
irradiated with natural sunlight, only 8% of the metolachlor photodecomposed in 30 days .
Humic substances retarded the photolysis of metolachlor in water . The estimated hydrolysis
half-life of metolachlor in water is 210 days .
AQUATIC FATE: Based on the value of Henry's Law constant , the rate of volatilization of
metolachlor from water will be negligibly small(1,SRC). The bioconcentration of metolachlor in
aquatic organisms will not be important and fish will rapidly depurate metolachlor when placed in
uncontaminated water .
ATMOSPHERIC FATE: From its vapor pressure of 3.14X10-5 mm Hg at 25 deg C ,
metolachlor is expected to be present partially in the vapor phase and partially in the particulate
form in air(2,SRC). Based on an estimation method , gas phase metolachlor may be removed
from the atmosphere with an estimated half-life of 1.8 hr due to reaction with photochemically
produced hydroxyl radicals. Partial removal of particulate metolachlor from the air may
occur by dry deposition. The fact that metolachlor has been detected in fog water and in
rainwater/snow(4-5) suggests it will be removed from the atmosphere by wet deposition as
Dissipation of cyanazine and metolachlor was detected following 2 and 3 applications,
respectively, to a clay loam soil at the Animal Research Center Farm, Ottawa between 1987 and
1990. Residue decline, leachability into the soil profile, movement into tile drainage water, and
contamination of the groundwater of the 2 herbicides were measured. The amount of each
herbicide applied to the soil surface was accounted for in the upper layer during the first week
following treatment. Cyanazine disappeared from the upper 15 cm of the soil in 181 days in 1987
and 90 days in 1988, with a calculated half-life disappearance of 27 and 12 days respectively.
Residues of cyanazine were not detected in the soil profile below 15 cm or in tile drainage water.
A single residue was detected in a sample of groundwater in 1988 at the detection level of 0.01
ug/l. The decline of metolachlor was followed in the upper 15 cm of the soil for 332, 364, and 370
days respectively in 1987, 1988 and 1989 and the half-life disappearance of 80, 99, and 142 days
were calculated. Residues of metolachlor were detected between 15 and 30 cm, but not below 30
cm in the soil profile. Metolachlor was detected in some tile drainage waters throughout the study
period. Between 0.003 and 0.01% of the metolachlor applied to the surface appeared in tile
drainage water following each of 3 applications. Metolachlor was present in groundwaters 1.2 to
4.6 m deep between the fall of 1988 to the summer of 1989. It was estimated that by the end of
the season between 0.06 and 0.19% of the metolachlor moved into the shallow groundwater
between the depths of 1.2 and 4.6 m.
|Drinking Water Impact|| SURFACE WATER: Metolachlor was detected at an average concentration of 0.23
ppb and a concentration range trace-2.70 ppb in 12 of 31 river waters in NJ . It was detected at
a concn range 0.046-0.273 ppb in water from the Mississippi River and its tributaries in 1988 .
During 1984-1985, the max. concn of metolachlor in waters from three stations along the Cedar
River, Iowa due to overland flow was less than 10 ppb . It was also detected in the mean concn
range 0.87-1.8 ppb in the Sacramento River above confluence with the San Joaquin River .
Metolachlor was detected at mean concn 1.23 ppb and 0.93 ppb in water from Upper Tuttle
Creek Lake and Lower Tuttle Creek Lake, respectively in Kansas . The concn range of
metolachlor in Honey Creek, Sandusky River and Maumee River during 1983-1986 was none
SURFACE WATER: Metolachlor was detected in 3.5%, 1.3% and 27.1% of water samples
from Grand River, Saugeen River and Thames River, respectively in Ontario, Canada between
1986-1990 . The concn range of metolachlor in 4 rural ponds in Ontario as a result of an
accidental spill and runoff was 0.6-190 ppb . Metolachlor was detected at a concn range
3.49-4.13 parts/trillion in water samples collected from Adige River, Italy in 1990 .
RAINWATER/FOGWATER: The concn of metolachlor in fogwater collected from Beltsville,
MD in 1984 was 1.96 ppb . Metolachlor was detected in 67 of 325 rainwater/snow samples
collected from two rural and one urban area in Iowa at a mean concn of 0.47 ppb and a max
concn of 2.70 ppb .
GROUNDWATER: A 1984 survey of U.S. groundwater reported detection of metolachlor in
waters from two (IA and PA) of 23 states with typical conc of 0.1-0.4 ppb . A more recent data
base (1988) developed to compile information about pesticide contamination in U.S. groundwater
from normal agricultural use reports detection of metolachlor in groundwater from 5 states (CT,
IA, IL, PA and WI) at a median concn of 0.4 ppb and a max. concn of 32.3 ppb . Metolachlor
has been detected in waters from private and rural domestic wells all across the U.S. with a
frequency of 1% and 0.22% of the samples contained metolachlor at or above 1 ppb . As of
1984, statewide screening of community and private wells in WI detected metolachlor in one well
GROUNDWATER: Metolachlor was detected in well waters in Nebraska with a frequency of
<1% and at a concn range of not detected to 2.32 ppb and a median concn of 0.06 ppb . In
some cases, artificial recharging of groundwater by farmland runoff may have caused metolachlor
contamination in Nebraska groundwater . Metolachlor has also been detected in the concn
range of 0.10 to 4.5 ppb in groundwater from Big Springs watershed in Iowa(3,4). In Kansas, 2%
of public water supply wells contained metolachlor at a max concn of 1.6 ppb . In a pilot study
during 1987-1988, metolachlor was detected in one well water from Comanche county, TX at an
average concn of 5.5 ppb(6). Several rural and farm wells in Ontario, Canada were contaminated
with metolachlor at concn not detected-110 ppb(3,7).
DRINKING WATER: During 1984-1987, metolachlor was detected at mean concn ranges of
2.0-5.7 ppb and <0.05-6.0 ppb (detection limit 0.05 ug/L) in raw and municipal drinking waters,
respectively, in an agricultural community in Ontario, Canada .