| Chemical Abstract Number (CAS #) |
15972608
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| Synonyms | Alachlor |
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Metachlor | Lasso | 2-Chloro-N-(2,6-diethylphenyl)-N-(methoxymethyl) acetamide |
| Analytical Methods |
EPA Method 505 |
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EPA Method 525 |
EPA Method 645 |
EPA Method 8081 |
| Molecular Formula | C14H20ClNO2 |
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| Use | HERBICIDE FOR GRASSES & BROADLEAF WEEDS ON CORN & SORGHUM,
SOYBEANS, PEANUTS, COTTON, VEGETABLES, FORAGE CROPS.
It is a selective pre and early post emergence herbicide for annual broadleaf control in crops such
as beans, beets, cabbage, corn, cotton, ornamentals, peanuts, peas, potatoes, sorghum, soybeans,
sugarcane, sunflowers, and tobacco.
Selective systemic herbicide for control of most annual grasses and many broad leaved weeds
in maize, sorghum, groundnuts, soya beans, lima beans, oilseed rape, brassicas, radish, oil radish,
cotton, sunflowers, sugar cane, potatoes, peas, tobacco, some ornamentals.
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| Consumption Patterns | 57% AS A SELECTIVE HERBICIDE FOR GRASS & BROADLEAF WEEDS ON
CORN & SORGHUM; 43% AS A SELECTIVE HERBICIDE FOR GRASS & BROADLEAF
WEEDS ON SOYBEANS; LESS THAN 1% AS A SELECTIVE HERBICIDE FOR GRASS &
BROADLEAF WEEDS ON PEANUTS, COTTON, VEGETABLES, & FORAGE CROPS
(1974)
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| Apparent Color | CRYSTALLINE SOLID ; CREAM COLORED SOLID AT ROOM TEMP ; Colorless to
yellow crystals
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| Odor | ODORLESS
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| Boiling Point | 100 DEG C @ 0.02 MM HG, 135 DEG C @ 0.3 MM HG
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| Melting Point | 40-41 DEG C
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| Molecular Weight | 269.77
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| Density | 1.133 @ 25 DEG C/15.6 DEG C
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| Sensitivity Data | SRP: Mild eye and skin irritant.
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| Environmental Impact | Alachlor is a herbicide used on a number of crops to control annual grasses and many
broad-leaved weeds. The release of alachlor in the environment occurs during the manufacture
and particularly as a result of its application in the field. In soil, alachlor is transformed to its
metabolites primarily by biodegradation. The half-life of alachlor disappearance from soil is about
15 days, although very little mineralization has been observed. Alachlor is highly to moderately
mobile in soil and the mobilization decreases with an increase in organic carbon and clay content
in soil. In water, both photolysis and biodegradation are important for the loss of alachlor,
although the role of photolysis becomes important in shallow clean water, particularly in the
presence of sensitizers. The bioconcentration of alachlor in aquatic organisms is not important.
The half-life of alachlor due to reaction with hydroxyl radicals in the atmosphere has been
estimated to be 2.1 hrs. Partial removal of alachlor will also occur as a result of dry and wet
deposition. Alachlor has been widely detected in surface water and groundwater around applied
farmlands. The applicators of the herbicide are the most likely people for exposure to alachlor via
inhalation and dermal routes.
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| Environmental Fate | TERRESTERIAL FATE: RESULTANT AVG PERSISTENCE OF RECOMMENDED
RATES: 6-10 WK BUT MAY VARY DEPENDING ON SOIL TYPE AND CLIMATE
CONDITIONS.
TERRESTRIAL FATE: In lab and field experiments, the persistence was in the order: propachlor
less than alachlor which was equal to dimethachlor which was less than metazachlor and
metazachlor was less than metolachlor. Increase of temp by 10 degrees reduced the half-life by a
factor of 1.9-2.5. The Arrhenius activation energy for alachlor was 57.0 kJ/mol.
The half-life of alachlor in soils was found to be 7 to 14 days. Four major metabolites of alachlor
were observed but only two were identified: 2-chloro-2',6'-diethylacetanilide and
1-chloro-acetyl-2,3-dihydro-7-ethylindole.
TERRESTRIAL FATE: Biodegradation will be the most important process by which alachlor will
be lost from most soils . Although biotransformation of alachlor from soil was rapid, very little
mineralization products were observed . This indicates that biotransformation proceeds via
cometabolism . Some loss of alachlor from soil will occur as a result of photolysis by sunlight,
but photolysis will not be competitive with biodegradation . The range of log Koc values
(2.08-2.18)(9) indicate that alachlor would have a high to medium mobility in soil .
Experimental results confirms that alachlor absorbs weakly to moderately to soil and the leaching
of alachlor from soil is high to medium(5-6). The presence of continuous pores or channels in soil
will increase the mobility of alachlor in soil(7-8).
TERRESTRIAL FATE: Volatilization of alachlor from poorly adsorbing moist soil to the
atmosphere may be significant if assisted by solar heating and high winds . Volatilization from
dry soil may not be significant(1,3). The half-life of alachlor in soil ranges from 4-49
days(1-2,4-7) with an average of 15 days in field soil(7). Alachlor residues may still be found in
some soils after 1 yr(6).
AQUATIC FATE: Under aerobic conditions, microorganisms in sewage and eutrophic lake water
transformed 10-21% of alachlor in 6 weeks . However, no mineralization product was isolated
leading to the conclusion that the biotransformation proceeded by cometabolism . The
disappearance of alachlor in groundwater free of aquifer materials (e.g., sand) was very slow and
the half-life was in the range 808-1518 days . When irradiated with 300 nm sunlamps, 1%
alachlor in aqueous solution degraded in 135 mins and the reaction was accelerated by
sensitizers . Based on a rate constant for the reaction of alachlor with hydroxyl radicals and
the concentration of hydroxyl radicals in a typical eutrophic water , the estimated half-life for
this reaction would be 38 days.
AQUATIC FATE: The rate of volatilization of alachlor from water will be negligibly small . In
a model ecosystem, 98.2% of alachlor transformed to 8 unidentified products in 33 days . Both
biotic and abiotic processes are probably important for the loss of alachlor from water. The
bioconcentration of alachlor in aquatic organisms will not be important and fish will rapidly
depurate alachlor when placed in uncontaminated water .
ATMOSPHERIC FATE: From its vapor pressure (2.2X10-5) mm Hg at 25 deg C , alachlor is
expected to be present partially in the vapor phase and partially in the particulate form in air .
Based on an estimation method , gas phase alachlor may be removed from the atmosphere with
a half-life of 2.1 hrs due to reaction with photochemically produced hydroxyl radicals.
Partial removal of particulate alachlor from the air may occur by dry deposition. The fact
that alachlor has been detected in rainwater(4-5) suggests it will be removed from the atmosphere
by wet deposition as well.
TERRESTRIAL FATE: It persists in soil 42-70 days, depending on conditions, loss being by
microbial metabolism.
Ring-(14)C-labeled alachlor and propachlor were studied in a model eco-system. Alachlor was
degraded into eight compounds and propachlor into seven compounds. None were identified. In
each case some of the material was unextractable. There was no evidence of magnification of the
two compounds or their metabolites in the food chain.
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| Drinking Water Impact | In regions where alachlor was used, analysis of selected wells revealed alachlorat 0.10 to
2.11 ug/l with one sample showing 9.1 ug/l.
SURFACE WATER: Alachlor was detected at an average concentration of 0.014 ppb and a
concentration range trace-0.13 ppb in 12 of 31 river waters in NJ . It was detected at a concn
range 0.006-0.900 ppb in water from the Mississippi River and its tributaries in 1988 , while its
concentration along the entire Mississippi River ranged not detected-0.840 ppb in 1984 .
During 1984-1985, the maximum concn of alachlor in waters from three stations along the Cedar
River, Iowa when overland flow was the major component of river discharge exceeded 20 ppb .
Alachlor was detected at mean concn 0.75 ppb and 0.71 ppb in water from Upper Tuttle Creek
Lake and Lower Tuttle Creek Lake, respectively in Kansas .
SURFACE WATER: Alachlor was detected in 0.4% and 1.4% of water from Grand River and
Thames River, Ontario, Canada between 1986-1990 . The concn range of alachlor in Honey
Creek, Sandusky River and Maumee River during 1983-1986 was none detected-54.8 ppb .
The levels of alachlor in three rural ponds in Ontario, Canada were 0.6-15 ppb . The concn of
alachlor in one rural pond in Ontario was 960 ppb as a result of an accidental spill . The concn
of alachlor in runoff water from a corn-producing area in Ontario, Canada ranged <0.2-37 ppb .
The average concn of alachlor on two occasions in runoff water from an agricultural basin in
east-central Iowa were 162 ppb and 64 ppb(6). The concn of alachlor in several other surface
waters in the U.S. are also available .
RAINWATER/FOGWATER: The concn of alachlor in fogwater collected from Beltsville, MD in
1984 was 1.45 ppb . Alachlor was detected in 30 of 79 rainwater samples collected from
several cities in New York state at a concn range 0.02-0.62 ppb .
GROUNDWATER: A 1984 survey of U.S. groundwater reported detection of alachlor in waters
from four (MD, IA, NE, PA) of 23 states with typical concn of 0.1-10 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 alachlor in groundwater from 14 states .
Alachlor has been detected in well waters from use areas in the U.S. with a frequency of <1%(7).
In one survey, alachlor was detected in 2 of 33 groundwater samples from Florida at an average
conc of 62.3 ppb in the two detectable samples . A 1980 screening of 1174 community wells
and 617 private wells in WI found alachlor in one well at a concn >10 ppb . It was also detected
in well waters in Nebraska with a frequency of <1% and at a concn range not detected-20.7 ppb
and a median concn of 0.09 ppb . In an earlier survey, alachlor was detected in 2 of 14 wells
from Nebraska at concn of 0.04 ppb . In some cases, artificial recharging of groundwater by
farmland runoff may have caused pesticide contamination in Nebraska groundwater(6).
GROUNDWATER: During a 1985-1987 Survey of 119 wells, springs and municipal drinking
water throughout AR, alachlor was detected in only one irrigation well at a concn of 5.5 ppb .
In 1990, 58 private wells in central Maine were monitored for pesticides and alachlor was found
in 7 well waters at a maximum conc of 0.36 ppb . In a statewide survey of farmstead wells in
KS, alachlor was detected in 1 of 100 wells at a concn 0.88-1.5 ppb(8). In 1984, several private
wells in a small town in upstate NY were found to be contaminated with alachlor at a maximum
concn of 660 ppb(6). Contamination of well waters from other states including IA, IL, MN, PA,
MA and MD has also been reported(7). Several farm wells in Ontario, Canada were found to be
contaminated with alachlor and in one well the concn was reported to be >1000 ppb(3-5).
DRINKING WATER: Alachlor was detected in the concn range 0.82-2.3 ppb in drinking waters
from three New Orleans drinking water plants . It was also detected at a mean concn range
0.47-2.8 ppb in three tap waters in Columbus, OH . During 1982-1985, alachlor was detected
at mean concn ranges of 0.9-3.4 and <0.05-2.2 ppb in raw and municipal drinking waters,
respectively of an agricultural community in Ontario, Canada .
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