Background:
Atrazine is a broad-spectrum herbicide that is mainly applied on corn, sorghum and sugarcane and has been found to contaminate drinking water in agricultural areas. It has been banned in Europe but is still one of the most widely used herbicides in many countries around the world. Atrazine was previously evaluated by the IARC Monographs programme in 1991 as non-classifiable as to its carcinogenicity to humans (Group 3). The herbicide alachlor and the fungicide vinclozolin have not been previously evaluated. Alachlor has been one of the most widely used herbicides, mainly on corn and soybeans, but its use is declining due to evolving regulation.  Vinclozolin is used mainly on fruit and vegetables. Exposures to these pesticides are highest in workers when handling the substances or during re-entry activities. Atrazine and alachlor are persistent in the environment.
Objectives and Methods:
A cancer hazard identification evaluation of the three pesticides was conducted by an international Working Group of 22 experts without conflicts of interest, following the procedures described in the preamble to the IARC Monographs. A systematic literature search was conducted, and the publicly available data on cancer in humans, cancer in experimental animals, and mechanistic studies with evidence relevant for the 10 key characteristics of carcinogens was screened and summarized. The Working Group then synthesized the literature for each evidence stream and integrated this into an overall evaluation for each agent following the Preamble methodology.
Results:
The Working Group finalized their evaluations during a meeting in Lyon, France from 28 October to 4 November 2025. There was limited evidence that atrazine causes non-Hodgkin lymphoma that is positive for the t(14;18) chromosomal translocation. There was limited evidence that alachlor causes laryngeal cancer in humans on the basis of evidence from a single, large, high-quality cohort study of pesticide applicators. Atrazine and alachlor were each classified as probably carcinogenic to humans (Group 2A), based on combinations of limited evidence for cancer in humans with sufficient evidence for cancer in experimental animals and strong mechanistic evidence in experimental systems. Vinclozolin was classified as possibly carcinogenic to humans (Group 2B), based on sufficient evidence for cancer in experimental animals and on strong mechanistic evidence in experimental systems.
Conclusions/Implications.
For all three pesticides, but especially for atrazine, which is used in many countries around the world, there is a potential for ongoing occupational and environmental exposure, particularly in low- and middle-income countries. The IARC evaluation can be used to identify potential carcinogenic hazards and to inform the development of exposure reduction strategies, thereby decreasing cancer risk, especially for workers.

Overview of the IARC Monograph Volume 140 evaluation of atrazine, alachlor and vinclozolin.