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Changes is atrazine carcinogen rating
by Brent Pringnitz

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January 30, 1999 - Various announcements in the media during the month focused on a change in the status of atrazine as a possible carcinogen.  This information came from a report issued by the International Agency for Research on Cancer which is part of the World Health Organization.

This IARC monograph, issued in October of 1998, listed agents that had recently been reviewed for their carcinogenic status.  This specific publication (Vol. 73) focused on materials which target specific organs in rodent bioassays.  As a result of this review, atrazine was changed from an overall rating of "Group 2B - possibly carcinogenic to humans" to "Group 3 - not classifiable as to carcinogenicity to humans."  The ratings table also lists an animal rating, which changed from "L - limited evidence" to "S - sufficient evidence."

The ratings for carcinogenicity issued by the IARC range from "1 - The agent (mixture) is carcinogenic to humans. The exposure circumstance entails exposures that are carcinogenic to humans." to "4 - The agent (mixture, exposure circumstance) is probably not carcinogenic to humans."

Reports concerning this change in atrazine rating also provided examples of other materials and their ratings.  Some other materials that received a "3" designation are:

Some materials listed as "2B" are:

These materials are not rated on their overall toxicity or hazard to humans.  These ratings provide a measure of their risk as a potential carcinogen only.  An explanation of the ratings as well as a complete list of all agents rated by the IARC is provided online.

At this time there are no changes to the atrazine label or atrazine management areas in Iowa.  In 1994 the U.S. Environmental Protection Agency (EPA) began a Special Review of all triazine herbicides (which includes atrazine) to determine the safety to human health and the environment.  This Special Review continues   and is not affected by the IARC reclassification.

Prepared by Brent Pringnitz, extension program specialist, Department of Agronomy, Iowa State University

For more information contact:
ISU Extension Agronomy
2104 Agronomy Hall
Ames, Iowa 50011-1010
Voice: (515) 294-1923
Fax: (515) 294-9985
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Common chemical and trade names are used in this publication. The use of trade names is for clarity by the reader. Inclusion of a trade name does not imply endorsement of that particular brand of herbicide and exclusion does not imply nonapproval.