Pesticides in the Environment


Pesticide Transport and Fate

Monitoring in the Environment

Methods for Measuring Human Exposure to the Agent

Exposure Pathways

Strategies for Preventing and Controlling Pesticides

Harmful Effects of Alachlor

Dose Response of Alachlor

Absorption, Distribution and Metabolism

Sites of Toxicity

Biomarkers of Disease and Molecular Mechanisms of Action

Risk Assessment

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Harmful Effects of Alachlor

Alachlor is an acetanilide herbicide of low acute toxicity, but repeated exposure has been reported to cause hepato-toxicity, irreversible uveal degeneration and tumor formation in rats (WHO, 1996).

Acute Toxicity
Alachlor is a lightly acute toxic herbicide. The oral LD50 of alachlor in rats is 930-1350 mg/kg. In the mouse, the LD50 is between 1910 and 2310 mg/kg. Clinical signs observed after oral dosing included ataxia, muscle tremors, hyperactivity, lethargy, dyspnea and convulsions.

  • The dermal LD50 in rabbits is 13,300 mg/kg. Skin irritation is slight to moderate.
  • The inhalation LC50 in rats was 1.04 mg/L for 4 hours of exposure. Clinical signs were related to eye and nasal irritation (EPA, 1997).
  • A single irritant effect on rabbit skin and eyes was observed following acute exposure. Alachlor was also a skin sensitizer in repeated exposures in humans.

Chronic toxicity
Alachlor has the potential to cause the following effects from a lifetime exposure at levels above the drinking water standards, MCL (Maximum Contaminant Level, 2 ppb): damage to liver, kidney, spleen; lining of nose and eyelids; cancer (EPA, 1996).

Non-carcinogenic toxicity
Chronic studies in rats and dogs showed effects on the liver, spleen, and kidneys. The iris and lung have also been affected (Extoxnet, 1996)

  • Reproductive effects
    High oral doses fed to rats during gestation resulted in maternal and fetal toxicity, but there was no indication that reproduction was affected. Alachlor does not appear to cause reproductive effects.
  • Teratogenic effects
    The results of many animal experiments indicate that alachlor is not likely to cause birth defects.
  • Mutagenic effects
    Alachlor does not appear to be mutagenic.

Human Data

  • There are 2 epidemiology studies related to exposure to alachlor in human. Mortality rates and cancer incidence were examined among manufacturing workers with potential exposure to alachlor. There are no cancer deaths among workers with 5 or more years of high exposure, and 15 years since first exposure. The conclusions in both studies suggested no appreciable effects of exposure to alachlor on workers mortality or cancer incidence (EPA, 1997).

Animal data

  • Laboratory animal feeding studies demonstrated oncogenic effects in 2 species, mice and rats, In mice, alachlor produced lung tumors, and in rats, stomach, thyroid and nasal turbinate tumors.
  • Only high doses of alachlor in rats developed stomach, thyroid, and nasal turbinate tumors. An 18-month mouse study with doses form 26 to 260 mg/kg/day showed an increase of lung tumors at the highest dose for females but not males. Because of lung tumors at the highest dose for only females and inconsistencies in these studies, the oncogenic potential of alachlor is uncertain (Extoxnet, 1996).

Structure-Activity Relationships (SAR) (OEHHA, 1997)

  • The Structure-Activity Relationship (SAR) is a means by which the effect of a toxic chemical on an animal, human or the environment can be related to its molecular structure. SAR is used in the evaluation for carcinogenic potential. Alachlor is structurally related to acetochlor, allidochlor, butachlor, metolachlor, propachlor etc. The EPA concluded that some of these chemicals have been shown to induce tumors at one or more of the same sites as alachlor.
  • Statistically significant increases in nasal tumors have been reported for acetochlor and butachlor in rats. Stomach tumors and thyroid follicular cell tumors have also been reported for acetochlor and butachlor in rats. These data support the evidence that nasal turbinate, stomach and thyroid tumors are related to exposure to these structurally-related compounds, including alachlor.


California Office of Environmental Health Hazard Assessment (OEHHA): ALACHLOR in Drinking Water (1997)

EPA, Alachlor: Reregistration Eligibility Decision (1997)

EPA, Consumer Factsheet on: ALACHLOR (1996)

Extension Toxicology Network Pesticide Information Profiles (1996)