International Agency for Research on Cancer (IARC) - Summaries & Evaluations

(Group 2B)

For definition of Groups, see Preamble Evaluation.

VOL.: 53 (1991) (p. 441)

CAS No.: 1912-24-9
Chem. Abstr. Name: 6-Chloro-N-ethyl-N'-(1-methylethyl)-1,3,5-triazine-2,4-diamine

5. Summary of Data Reported and Evaluation

5.1 Exposure data

Atrazine was introduced in 1957. It is now one of the most extensively used herbicides worldwide, with US production of at least 50 000 tonnes per annum since 1980. It is widely used on maize and to a lesser extent on a variety of other crops.

Atrazine has been formulated as wettable powders, granules and liquid formulations.

Exposure can occur during production and application of atrazine and via contaminated ground- and surface water. Exposure could also occur from consumption of foods containing residues. Atrazine residues were not detected in large-scale surveys of foods products in Canada and the USA.

5.2 Carcinogenicity in humans

One population-based case-control study in northern Italy found an elevated risk for ovarian cancer in women considered to have been exposed to triazine herbicides. A hospital-based case-control study in the same area found an elevated risk for ovarian tumours among women exposed to herbicides, including triazine herbicides.

A case-control study from Kansas, USA, indicated an association between self-reported use of triazine herbicides and risk for non-Hodgkin's lymphoma. A nonsignificant doubling of the risk was found in the absence of exposure to phenoxyacetic acid herbicides and uracils. In another study in Kansas, USA, in which apparently the same controls were used, self-reported use of triazine herbicides was associated with a slight excess risk of colon cancer, as was employment on a farm in general.

In two case-control studies from Iowa and Minnesota, USA, there was no association between self-reported use of atrazine and leukaemia, whereas a slightly increased risk was suggested for a subgroup of lymphomas.

In a case-control study in Nebraska, USA, a nonsignificant elevation in risk for non-Hodgkin's lymphoma was associated with self-reported use of atrazine. Risks were greater among men with 16 or more years of use than among those with a shorter duration.

These seven studies were considered to provide some evidence for the carcinogenicity of exposure to triazine herbicides. Complex exposures and insufficient reporting made it difficult to evaluate the carcinogenicity of individual triazine herbicides, including atrazine.

5.3 Carcinogenicity in experimental animals

Atrazine was tested for carcinogenicity in one experiment by oral administrationm to rats, producing increased incidences of mammary tumours (mainly benign) in males and of uterine adenocarcinomas and tumours of the haematopoietic system in females. It was also tested by intraperitoneal administration to mice; it was stated in a preliminary report to have produced an increase in the incidence of lymphomas.

5.4 Other relevant data

Atrazine was embryotoxic and embryolethal but not teratogenic in rats and rabbits when administered at maternally toxic doses.

Atrazine and its de-ethylated metabolite have been shown to alter the activity of some testosterone-metabolizing enzymes in the rat pituitary and hypothalamus, and to decrease hormone-receptor binding in the prostate.

No data were available on the genetic and related effects of atrazine in humans.

Atrazine induced DNA strand breaks in stomach, liver and kidney cells but not lung cells of rats treated orally. Chromosomal aberrations were induced in plants and insects, but not in cultured rodent cells. Aneuploidy was induced in Drosophila melanogaster and fungi. Atrazine induced gene mutation in plants, but not in bacteria or cultured rodent cells.

5.5 Evaluation

There is inadequate evidence in humans for the carcinogenicity of atrazine.

There is limited evidence in experimental animals for the carcinogenicity of atrazine.

In making the overall evaluation, the Working Group took into consideration the following supporting evidence. The increased risks for tumours that are known to be associated with hormonal factors, which were observed in studies of both animals and human beings, are consistent with the known effects of atrazine on the hypothalamic-pituitary-gonadal axis.

Overall evaluation

Atrazine is possibly carcinogenic to humans (Group 2B).

Subsequent evaluation: Vol. 73 (1999)


For definition of the italicized terms, see Preamble Evaluation.

Last updated: 30 September 1999

    See Also:
       Toxicological Abbreviations
       Atrazine (HSG 47, 1990)
       Atrazine (ICSC)
       Atrazine  (IARC Summary & Evaluation, Volume 73, 1999)