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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Sites of Toxicity

Alachlor has been shown to be toxic to several systems in animal studies. Slight irritation of eyes and skin are the only toxic effects proven in humans. There are no other human studies that prove toxicity in the human system. Evidence from animal studies have shown that alachlor and some of its’ metabolites can cause damage to the liver, nasal mucosa, thyroid gland, and glands of the stomach.

Nasal Mucosa

The nasal mucosa is the membrane that covers the nasal cavity. In rodents, alachlor has been found to cause tumors in the nasal mucosa that lines the nasal turbinate. The nasal turbinate is a structure composed of fine bones within the navel cavity and can be seen in the figure below.

While studies in rats show definite evidence of nasal tumors, studies done on mice and monkeys produced very different results at similar doses. It is thought that the mechanisms required for producing the metabolites that induce nasal tumors are species dependent. Humans possess the metabolic pathway to create the toxic metabolites, but they are not as efficient as the rat pathways.

Adapted from © 1998 May Cheney

Thyroid Gland

Incidences of thyroid tumors were reported in rat studies. There is evidence that alachlor and its metabolites are not directly toxic to the thyroid. It is thought that toxicity to the liver causes an increase in the metabolism of thyroid hormones. This increased metabolism then promotes the over production of thyroid stimulating hormone (TSH). The increased levels of TSH may be responsible for the onset of tumors in the thyroid (Wilson et al, 2003).


Studies done on rat liver cells have shown that alachlor may cause damage to cells in the liver preventing them from functioning properly (Bonfanti et al, 1992; El-Sakka et al, 2002). When a chemical is toxic to the liver, it is called a hepatotoxin.


Alachlor consistently causes malignant tumors of the glandular stomach in animal tests. The same pathways exist in humans (EPA, 1997). However, the doses of alachlor at which rats exhibit stomach tumors are beyond what would be considered average doses for the general population and for people who work with pesticides.


Bonfanti, Marina, Pietro Taverna, Lucia Chiappetta, Pia Villa, Maurizio D’Incalci, Renzo Bagnati, and Roberto Fanelli. 1992. DNA damage induced by alachlor after in vitro activation by rat hepatocytes. Toxicology. 72:2:207-219.

El-Sakka, Sahar, Ezz El-Din, and Mohamed S. Abdel-Rahman. 2002. In Vitro Hepatoxicity of Alachlor and its By-Products. Journal of Applied Toxicology. 22: 31-35.

EPA. Alachlor Reregistration Eligibility Decision, 1997

Starr, Cecie and Beverly McMillan. 2001. Human Biology Fourth Edition. Brooks/Cole: California.

Wilson, A.G.E., D.C. Thake, W.E. Haydens, D.W. Brewster, and K.J. Hotz. 2003. Mode of Action of Thyroid Tumor Formation in the Male Long-Evans Rat Administered High Doses of Alachlor. Fundamental and Applied Toxicology.