United States
Environmental Protection
Agency
Office of Water
4601
EPA811-F-95-003b-T
October 1995
&EPA
National Primary Drinking
Water Regulations
Alachlor
CHEMICAL/ PHYSICAL PROPERTIES
CAS NUMBER: 15972-60-8
COLOR/ FORM/ODOR:
Available in granular, emulsifiable
concentrate and flowable formulations
M.P.: 40-41 °C B.P.: N/A
VAPOR PRESSURE: Negligible
DENSITY/SPEC. GRAV.: 1.133 at 25° C
OCTANOL/WATER PARTITION (Kow):
Log Kow = 2.63 and 3.53
SOLUBILITY: 0.14 g/L of water at 23" C;
Slightly soluble in water
SOIL SORPTION COEFFICIENT:
Koc = 2.08 to 2.28; medium to.
highmobility in soil
ODOR/TASTE THRESHOLDS: N/A
BlOCONCENTRATION FACTOR:
BCF = 6 in fish; not expected to
bioconcentrate in aquatic organisms.
HENRY'S LAW COEFFICIENT:
3.2x10-" to 1.2x10-'° atrn-cu m/mole;
TRADE NAMES/SYNONYMS:
Alochlor; Lasagrin; Lassagrin; Lasso;
Lazo; Metachlor; Pillarzo; Alanox;
Alanex; Chimichlor
DRINKING WATER STANDARDS
MCLG: zero mg/L
MCL: 0.002 mg/L
HAL(child): 1 day: 0.1 mg/L
10-day: 0.1 mg/L
HEALTH EFFECTS SUMMARY
RELEASE PATTERNS
The major source of environmental release of alachlor
is through its manufacture and use as a herbicide.
Alachlor was detected in rural domestic well water by
EPA's National Survey of Pesticides in Drinking Water
Wells. EPA's Pesticides in Ground Water Database
reports detections of alachlor in ground water at concen-
trations above the MCL in at least 15 States.
Acute: EPA has found alachlor to potentially cause
slight skin and eye Irritation from acute exposures at ENVIRONMENTAL FATE
levels above the MCL.
Drinking water levels which are considered "safe" for
short-term exposures: Fora 10-kg child consuming 1 liter
of water per day, upto a ten-day exposure to 0.1 mg/L.
Chronic: Alachlor has the potential to cause damage
to the liver, kidney, spleen, nasal mucosa and eye from
long-term exposure at levels above the MCL.
Cancer: There is some evidence that alachlor may
have the potential to cause cancer from a lifetime expo-
sure at levels above the MCL.
USAGE>PATTERNS
Alachlor is a herbicide used for preemergent control of
annual grasses and broadleaf weeds in crops, primarily
on corn and sorghum (57%) and soybeans (43%). Appli-
cation to peanuts, cotton, vegetables and forage crops
contributes to less than 1% of its use. Alachlor is the
•second most widely used herbicide in the United States,
with particularly heavy use on com and soybeans in
Illinois, Indiana, Iowa, Minnesota, Nebraska, Ohio, and
Wisconsin.
In soil, alachlor is transformed to its metabolites prima-
rily by biodegradation. The half-life of alachlor disappear-
ance from soil is about 15 days, although very little
mineralization has been observed. The biodegradation
of alachlor in soil under spill conditions will be very slow
due to toxicity. Photodegradation in soil is slow.
Log Koc values for alachlor have largely been in the
range 2.08-2.28, indicating that alachlor would have a
high to medium mobility in soil, and that the leaching of
alachlor from soil is high to medium. The adsorption of
alachlor increases with an increase in organic content,
clay content and surface area of soil. Alachlor was not
detected in groundwater from a soil with high organic and
clay content. This is probably due to longer residence
time in this soil allowing the degradation of alachlor
before it reached the water table. The presence of con-
tinuous pores or channels in soil will increase the mobility
of alachlor in soil.
The evaporation of alachlor from soil will increase as
the moisture content and temperature of the soil is
increased. Increase in alachlor sorption in soil will de-
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crease evaporation as evidenced by slower evaporation
with the increase in clay and organic matter content of
soil. It has been concluded trbt the loss of alachlor from
soil will be moderate and an estimated 3.5-6.5 kg/ha/yr or
more alachlor will be lost from treated field. The estimated
half-life of alachlor evaporation from soil is in the range 12
to >200 days.
In water, both photolysis and biodegradation are im-
portant for the loss of alachlor, although the role of
photolysis becomes important in shallow clean water,
particularly in the presence of sensitizers.
The mineralization of alachlor in groundwater aquifers
was slow and <1% mineralization was observed in 30
days. 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. Between alachlor
concentrations of 1-5 ppb, the disappearance rate was
faster at higher temperatures, and in groundwater taken
from shallower depths. The lower biotransformation rates
in anaerobic groundwater compared to aerobic ground-
water may be due to less microbial activity or the absence
of alachlor degraders in anaerobic samples. The mea-
sured and estimated Henry's Law constant (H) for ala-
chlor at ambient temperatures is in the range 3.2X10-8 to
1.2X10-10 atm-cu m/mole, so volatilization of alachlor
from water will not be 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.
The bioconcentration of alachlor in aquatic organisms
is not important. Whole body bioconcentration factor
(BCF) for alachlor in fathead minnow (Pimephales
promelas) was measured to be 6. Alachlor was rapidly
eliminated upon transfer offish in uncontaminated water
with 81% and 98% being eliminated after 24 hr and 14
days, respectively. The BCF value for alachlor vapor in
azalea plant leaves was experimentally determined in
greenhouse experiments to be 2.8X10+5, with elimina-
tion of alachlor from the leaves starting at 15 days.
OTHER REGULATORY INFORMATION
MONITORING:
FOR GROUND/SURFACE WATER SOURCES:
INITIAL FREQUENCY- 4 quarterly samples every 3 years
REPEAT FREQUENCY- If no detections during initial round:
2 quarterly per year if serving >3300 persons;
1 sample per 3 years for smaller systems
TRIGGERS - Return to Initial Freq. if detect at >0.0002 mg/L
METHOD NUMBERS
505; 507; 525.2; 508.1
ANALYSIS:
REFERENCE SOURCE
EPA 600/4-88-039
TREATMENT:
BEST AVAILABLE TECHNOLOGIES
Granular Activated Charcoal
FOR ADDITIONAL INFORMATION:
* EPA can provide further regulatory and other general information:
• EPA Safe Drinking Water Hotline - 800/426-4791
4 Other sources of lexicological and environmental fate data include:
• Toxic Substance Control Act Information Line - 202/554-1404
• Toxics Release Inventory, National Library of Medicine - 301/496-6531
• Agency for Toxic Substances and Disease Registry - 404/639-6000
• National Pesticide Hotline - 800/858-7378
October 1995
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