Technical Factsheet on: ALACHLOR
List of Contaminants
As part of the Drinking Water and Health pages, this fact sheet is part of a larger publication:
National Primary Drinking Water Regulations
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
Acute: EPA has found alachlor to potentially cause slight skin
and eye irritation from acute exposures at levels above the MCL.
Drinking water levels which are considered "safe" for short-term
exposures: For a 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 exposure 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%). Application 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 corn and soybeans
in Illinois, Indiana, Iowa, Minnesota, Nebraska, Ohio, and
Wisconsin.
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
concentrations above the MCL in at least 15 States.
Environmental Fate
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. 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 continuous
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 decrease evaporation
as evidenced by slower evaporation with the increase in clay and
organic matter content of soil. It has been concluded that 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 important 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 groundwater may be due
to less microbial activity or the absence of alachlor degraders
in anaerobic samples. The measured and estimated Henry's Law
constant (H) for alachlor 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 of fish 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 elimination of alachlor from the
leaves starting at 15 days.
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
Bioconcentration Factor: BCF = 6 in fish; not expected to
bioconcentrate in aquatic organisms.
Henry's Law Coefficient: 3.2x10-8 to 1.2x10-10 atm-cu m/mole;
Trade Names/Synonyms: Alochlor; Lasagrin; Lassagrin; Lasso; Lazo;
Metachlor; Pillarzo; Alanox; Alanex; Chimichlor
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
Analysis:
| Reference Source |
Method Numbers |
| EPA 600/4-88-039 |
505; 507; 525.2; 508.1 |
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
Other sources of toxicological 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
List of Contaminants
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