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The information in this profile may be out-of-date. It was last revised in 1996. EXTOXNET no longer updates this information, but it may be useful as a reference or resource.

Please visit the National Pesticide Information Center (NPIC) to find updated pesticide fact sheets. If you don't find a fact sheet related to your question, feel free to call 1-800-858-7378. NPIC is open five days a week from 8:00am to 12:00pm Pacific Time.

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E X T O X N E T

Extension Toxicology Network

Pesticide Information Profiles

A Pesticide Information Project of Cooperative Extension Offices of Cornell University, Oregon State University, the University of Idaho, and the University of California at Davis and the Institute for Environmental Toxicology, Michigan State University. Major support and funding was provided by the USDA/Extension Service/National Agricultural Pesticide Impact Assessment Program.

EXTOXNET primary files maintained and archived at Oregon State University

Revised June 1996

Alachlor

Trade and Other Names: Trade names of commercial herbicides containing alachlor include Alanex, Bronco, Cannon, Crop Star, Lariat, Lasso, and Partner. It mixes well with other herbicides such as Bullet, Freedom, and Rasta, and is found in mixed formulations with atrazine, glyphosate, trifluralin, and imazaquin.

Regulatory Status: Alachlor is a Restricted Use Pesticide (RUP). RUPs may be purchased and used only by certified applicators. The EPA categorizes it as toxicity class III - slightly toxic. However, alachlor products bear the Signal Word DANGER on their labels because of their potential to cause cancer in laboratory animals.

Chemical Class: aniline

Introduction: Alachlor is an aniline herbicide used to control annual grasses and broadleaf weeds in field corn, soybeans, and peanuts. It is a selective systemic herbicide, absorbed by germinating shoots and by roots. It works by interfering with a plant's ability to produce protein and by interfering with root elongation.

This compound is one of the most highly used herbicides in the U.S. Over 50 million pounds were applied annually in 1990. It is available as granules or emulsifiable concentrate.

Formulation: It is available as granules or emulsifiable concentrate.

Toxicological Effects:

• Acute toxicity: Alachlor is a slightly toxic herbicide. The LD50 of alachlor in rats is between 930 mg/kg and 1350 mg/kg. In the mouse, the LD50 is between 1910 and 2310 mg/kg [60]. The dermal LD50 in rabbits is 13,300 mg/kg, but some of the formulated materials can be more toxic, with dermal LD50 values ranging from 7800 to 16,000 mg/kg [58]. Skin irritation is slight to moderate. The inhalation LC50 in rats is reportedly greater than 23.4 mg/L for 6 hours of exposure [1,60].
• Chronic toxicity: A 90-day study on rats and dogs given diets containing low to moderate amounts of alachlor (1 to 100 mg/kg/day) showed no adverse effects [58]. However, a 6-month dog study showed liver toxicity at all doses above 5 mg/kg/day, and a 1-year study established that above 1 mg/kg/day, alachlor causes effects in the liver, spleen, and kidney. In 2-year rat studies, doses above 2.5 mg/kg/day caused irreversible degeneration of the iris and related eye structures [60].
• Reproductive effects: High oral doses (150 or 400 mg/kg/day) fed to rats during gestation resulted in maternal and fetal toxicity, but there was no indication that reproduction was affected [60,61]. Alachlor does not appear to cause reproductive effects.
• Teratogenic effects: Doses of up to 150 mg/kg/day fed to rabbits on days 7 through 19 of pregnancy did not result in any birth defects [6]. Similar studies in rats at doses up to 400 mg/kg/day did not result in birth defects, but toxic effects in the mothers and offspring were seen at the highest dose. These data indicate that alachlor is not likely to cause birth defects.
• Mutagenic effects: Alachlor does not appear to be mutagenic. Mutagenicity assays with a variety of microbial strains at numerous concentrations of alachlor were all negative [60,61].
• Carcinogenic effects: Rats given high doses of alachlor developed stomach, thyroid, and nasal turbinate tumors [60]. An 18-month mouse study with doses from 26 to 260 mg/kg/day showed an increase of lung tumors at the highest dose for females but not males [60]. Because of inconsistencies in these studies, the oncogenic potential of alachlor is uncertain [62].
• Organ toxicity: Long-term studies in rats and dogs showed effects on the liver, spleen, and kidneys. The iris and lung have also been affected.

• Fate in humans and animals: Rats given a single low dose of alachlor (14 mg/kg) eliminated most of it within the first 48 hours [60]. Nearly all of the compound was eliminated in 10 days; a third to a half of the alachlor and its breakdown products were excreted in urine and nearly a half in feces. Rats absorbed close to 75% of a single low dose (14 mg/kg) through skin while only 8 to 10% was absorbed through the skin in monkeys [60].

Ecological Effects:

• Effects on birds: Alachlor is slightly to practically nontoxic to wildfowl. Alachlor has a 5-day dietary LC50 of greater than 5000 ppm in young mallard ducks and bobwhite quail [58]. The LD50 of alachlor in other mallard ducks was greater than 2000 mg/kg [63]. The LC50 of alachlor in pheasants is greater than 10,000 ppm [8].
• Effects on aquatic organisms: Alachlor is moderately toxic to fish. The LC50 (96-hour) for alachlor is 2.4 mg/L in rainbow trout, 4.3 mg/L in bluegill sunfish, 6.5 mg/L in catfish, and 4.6 mg/L in carp [1,8]. It is only slightly toxic to crayfish, with a LC50 (96-hour) of 19.5 mg/L [8,37]. The bioaccumulation factor in the channel catfish is 5.8 times the ambient water concentration, indicating that alachlor is not expected to accumulate appreciably in aquatic organisms [8].
• Effects on other organisms: Alachlor is not toxic to bees. It is practically nontoxic to earthworms [61].

Environmental Fate:

• Breakdown in soil and groundwater: Alachlor has a low persistence in soil, with a half-life of about 8 days [1,8]. The main means of degradation is by soil microbes [58]. It has moderate mobility in sandy and silty soils, and thus can migrate to groundwater [60]. The largest groundwater testing program for a pesticide, the National Alachlor Well Water Survey, was conducted throughout the last half of the 1980s. Over 6 million private and domestic wells were tested for the presence of alachlor. Less than 1% of all of the wells had detectable levels of alachlor [64]. In the wells where the compound was detected, concentrations ranged from 0.1 to 1.0 ug/L, with the majority having concentrations around 0.2 ug/L [64].
• Breakdown in water: Alachlor breaks down rapidly in natural water, primarily due to the action of microorganisms. The breakdown rate is much slower in water with no oxygen [58].
• Breakdown in vegetation: Absorption is primarily by germinating shoots and it is readily translocated throughout the plant [37]. Higher concentrations appear in the vegetative parts than in the reproductive parts of the plant. Alachlor is rapidly metabolized to water-soluble products in plants [19]. It is almost completely metabolized within 10 days [8].

Physical Properties:

• Appearance: Alachlor is a colorless to yellow crystal compound [1].
• Chemical Name: 2-chloro-2',6'-diethyl-N-(methoxymethyl) acetanilide [1]
• CAS Number: 15972-60-8
• Molecular Weight: 269.77
• Water Solubility: 242 mg/L @ 25 C [1]
• Solubility in Other Solvents: s. in most organic solvents [1]
• Melting Point: 40 C [1]
• Vapor Pressure: 2.9 mPa @ 25 C [1]
• Partition Coefficient: 2.8998 [58]
• Adsorption Coefficient: 170 [11]

Exposure Guidelines:

• ADI: 0.0025 mg/kg/day [12]
• MCL: 0.002 mg/L [65]
• RfD: 0.01 mg/kg day [13]
• PEL: Not Available
• HA: Not Available
• TLV: Not Available

Basic Manufacturer:

Monsanto Company
800 N. Lindbergh Blvd.
St. Louis, MO 63167

• Phone: 314-694-6640
• Emergency: 314-694-4000

References:

References for the information in this PIP can be found in Reference List Number 10

DISCLAIMER: The information in this profile does not in any way replace or supersede the information on the pesticide product labeling or other regulatory requirements. Please refer to the pesticide product labeling.