| Chemical Abstract Number (CAS #) |
330552
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| Synonyms | Linuron |
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Urea, N'-(3,4-dichlorophenyl)-N-methoxy-N-methyl- | Afalon | Lorox | Linex | Linurex | 1-Methoxy-1-methyl-3-(3,4-dichlorophenyl)urea |
| Analytical Methods |
EPA Method 553 |
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EPA Method 632 |
| Molecular Formula | C9H10Cl2N2O2 |
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| Use | Selective herbicide recommended for pre-emergence use in asparagus, beans, cotton,
maize, peas, potatoes, soyabeans, and for pre-emergence or post-emergence use in carrots and
winter wheat.
Controls germinating and newly established broadleaf weeds and grasses in crops such as
sorghum, wheat (Pacific Northwest only), celery and parsnips. It is also used for short-term
control of annual weeds in noncropland areas such as roadsides and fence rows. With a suitable
surfactant as a directed spray in certain crops, it controls weeds up to 5 inches high; without
surfactant as a non-directed postemergence spray in carrots, it controls emerged grasses up to 2 in
and broadleaf weeds up to 6 in high.
Control of annual grass and broad-leaved weeds, and some seedling perennial weeds in
artichokes parsley, fennel herbs and spices celeriac, onions, leeks, garlic field beans
cereals sorghum flax, sunflowers, sugar cane, ornamentals, established vines, bananas,
cassave, coffee, tea, rice, groundnuts, ornamental trees and shrubs, and other crops.
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| Apparent Color | WHITE CRYSTALLINE SOLID; COLORLESS CRYSTALS; Fine flakes or coarse
powder
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| Odor | ODORLESS
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| Melting Point | 93-94 DEG C
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| Molecular Weight | 249.11
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| Sensitivity Data | MAY IRRITATE EYES, NOSE, THROAT, & SKIN.
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| Environmental Impact | Linuron, 3-(3,4-dichlorophenyl)-1-methoxy-1-methylurea, may be released to the
environment during its application as a herbicide on soybean, carrots, cotton, potatoes, carrots,
and celery. Releases will be primarily to soil, although releases to water may occur from spills or
runoff. Releases may also occur during production, formulation, preparation for spraying,
cleanup, transport, and storage. Linuron is strongly adsorbed to soil and will generally remain in
the upper 2.5 cm of soil and should photolyze on the soil surface. In most soils, at normal
application rates, linuron degrades within 3-4 months. Linuron residues do not accumulate in soil
and progressive buildup of residues is not observed after repeated treatment. If released in water,
linuron will adsorb to sediment and particulate matter in the soil column and photolyze in surface
waters. Bioconcentration in fish is minimal. In the atmosphere, linuron will exist predominantly as
the vapor and degrade by reaction with photochemically produced hydroxyl radicals with an
estimated half-life of 11.4 hr. Human exposure will be primarily occupational. Occupational
exposure will be by inhalation and dermal contact and most generally would occur during
formulation and application of the herbicide and by touching soil and vegetation that were
sprayed. The general population may be exposed to linuron by ingesting contaminated vegetables,
primarily carrots.
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| Environmental Fate | ACCUM FROM ANNUAL APPLICATIONS TO THE SAME SOIL IS NOT A
PROBLEM.
Terrestrial fate: Movement by leaching is least in soils high in clay and/or organic matter;
greatest in sand. Bioassays of oats have shown no significant soil residues 3 to 4 months after
treatment at selective rates, and fall-sown cover crops have grown normally. Half-life under field
conditions is 2 to 5 mo.
TERRESTRIAL FATE: When applied to soil, linuron will adsorb moderately strongly and
remain primarily in the upper 2.5 cm of the soil. It should photolyze on the soil surface. Loss due
to biodegradation will also occur and will increase with increasing organic matter and moisture
content of the soil and temperature(1,3,5). In most soils, at normal application rates, linuron
degrades within 3-4 months . The dissipation of linuron was followed in field plots planted with
potatoes and treated with linuron at 1 and 2 kg/ha . The disappearance of linuron was very fast
and followed first order kinetics with a half life of 25 and 22 days, respectively, at the two
application rates . After about 75 days, the residual concn of linuron in the soil was constant,
suggesting that a small amount of linuron is strongly adsorbed to soil colloids and not available to
microbial attack . In test field plots in an onion growing area of Ontario, 64% of linuron had
dissipated in 5 months from the organic soil (92% organic matter) . It was concluded that
linuron residues did not accumulate in soil in onion farms of area growers .
TERRESTRIAL FATE: The half-life of linuron in cropped fields was 8-25 weeks; residues were
undetectable after 6 mo(1-2). No progressive buildup was observed after repeated treatment(1-2).
Four weeks after a half normal, normal, and double normal spray of linuron in May on corn,
carrots, bean and potato crops planted in loamy soil, an average of 40% of the applied dose was
recovered . After 3 months, only 25% of the linuron was recovered . At the end of the winter
months, <0.4% of the linuron was recovered . In Greenhouse experiments linuron's persistence
was 25-60 weeks .
AQUATIC FATE: If released in water, linuron will adsorb to sediment and particulate matter in
the water column. Linuron biodegrades in soil and therefore would be expected degrade in
aerobic sediment. Linuron degrades in anaerobic sediment, although no degradation rates are
available . Photolysis will occur in surface waters. In one experiment, 43% of linuron exposed
to sunlight outdoors was photolyzed in 24 days . While linuron biodegrades in soil, no linuron
biodegraded when incubated with river water and sewage for 4 months . Linuron would not be
expected to volatilize or hydrolyze. Bioconcentration in aquatic organisms should be minimal.
After linuron (1 ppm) was added to each of three 1 cu m outdoor ecosystems, linuron concns in
the water columns declined exponentially over the 42-day experiment; the calculated half-lives
ranged from 16 to 42 days . It was not determined what happened to the linuron. The half-life
of linuron in Lake Balatan (Hungary) water was 10 weeks .
ATMOSPHERIC FATE: In the atmosphere, linuron will primarily exist in the vapor phase . In
the vapor phase, it will degrade by reaction with photochemical-produced hydroxyl radicals with
an estimated half-life of 11.4 hours . It will also undergo direct photolysis, although there are
no data as to how fast photolysis might proceed in air.
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| Drinking Water Impact | GROUNDWATER: In a survey of 201 rural wells in 8 agricultural areas of Missouri,
linuron was found in 2 wells at 1.8 and 1.9 ppb . These wells were located in areas planted with
soybeans. Sampling was performed in December. According to EPA's Pesticides in Groundwater
database, linuron has been found only in Wisconsin groundwater; the contamination was judged
to result from normal agricultural use . The concn median and maximum were 1.9 and 2.7 ppb,
respectively . In a 1986-1987 study of 179 farm wells in Ontario with suspected contamination,
28 wells contained linuron above the 0.1 ppb detection limit . In a British study in which 700
samples of rivers, reservoirs and groundwaters were analyzed, linuron was not detected in any
groundwater(DL 0.2 ug/l) .
SURFACE WATER: The concn of linuron was monitored at 7 stations on Lake Erie tributaries
draining agricultural watersheds from 1983 to 1991, during which time over 4000 samples were
analyzed . The maximum and 95th percentile linuron concns at these stations ranged from
1.36-24.77 ppb and 0.27-2.07 ppb, respectively . The time-weighted average and
flow-weighted average concns ranged from 0.04-0.17 ppb and 0.00-0.20 ppb . Twenty five
water samples taken from 4 Michigan rivers during runoff season, from April to September 1985,
and analyzed for linuron were above the detection limit and linuron levels ranged from
0.146-2.813 ppb . While linuron is used on corn and soybean fields bordering Chesapeake Bay
and its tributaries, including one in which an estimated 45,000 kg of linuron drains into the
discharge basin, <0.2 ppb of linuron was found in 79 water samples from tributaries of
Chesapeake Bay during two successive summers . A farm pond in Ontario contained 12 ppb of
linuron that was attributed to runoff .
EFFL: Runoff was collected after each rainfall or series of rainfalls from test plots (silty clay
loam graded to a slope of 0.2%) planted with soybeans in the 2 to 4 month period following
treatment with linuron as a preemergence herbicide. Concns of linuron in runoff in three years
were: trace - 28 ppb, trace - 14 ppb, and trace - 124 ppb (trace = <10 ppb), respectively .
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