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Atrazine History

Atrazine’s history dates back more than 50 years.   Atrazine was first registered for use in 1959 and EPA recently recommended its re-registration after a comprehensive, 10-year safety review.

Historical Summary of Atrazine Registration Process
1959 First registrations for atrazine in US Over a 45-year period, atrazine has become one of the most widely used herbicides in corn, grain sorghum, sugar cane and other crops. Atrazine herbicide products offer the following benefits: 

• Effective, broad spectrum weed control leads to high crop yields

• Low treatment cost

• Application flexibility – atrazine can be applied prior to, during or after planting the crop, or after crop emergence, so it fits a wide variety of cropping systems

• Fits soil-saving conservation tillage systems

• Low risk of crop injury

• Important in management of weed resistance

• Low potential for drift

Late 1980s Researchers find higher incidence of tumors in one species of rat (Sprague-Dawley) when exposed to high levels of atrazine. Based on research with the Sprague-Dawley rat, atrazine was classified as a “possible human carcinogen (class C).”
Early 1990s Due to wide acceptance of atrazine in Midwest agriculture, stewardship programs were developed to minimize exposure to groundwater and surface water sources. A combination of changing cultural practices (application rates and timing, buffer zones around water sources, etc.) and the increase in conservation tillage led to a dramatic reduction in the number of detects of atrazine in water sources. In a study by the US Geological Survey (USGS), atrazine levels in 53 Midwestern streams (following spring applications) decreased about 47 percent between the years 1989-90 and 1994-95. Decreasing trends of atrazine levels in water continue today.
November 1994 Triazine Special Review is launched. The Special Review is a comprehensive look at all environmental safety, human toxicity, water quality and other data pertinent to the re-registration of triazine herbicides. Through the course of this review, EPA has analyzed hundreds of research studies and received more than 80,000 public comments (mostly from supportive growers, commodity groups and university researchers), in addition to conducting public forums to review the risk assessments.
June 2000 EPA Scientific Advisory Panel recommends reclassification of atrazine as “not likely” to cause cancer in humans. A special EPA Scientific Advisory Panel determined that the effect of increased tumors seen exclusively in the Sprague-Dawley rat was not relevant to humans and recommended that atrazine be reclassified as “not likely to be a human carcinogen.” This echoes a ruling in 1998 by the World Health Organization’s International Agency for Research on Cancer (IARC), which re-categorized atrazine as “not classifiable as to carcinogenicity in humans.” Regulatory reviews in Australia and the European Union also support atrazine’s safety to humans and the environment.
January 19, 2001 EPA Preliminary Human Health Risk Assessment published. The preliminary Human Health Risk Assessment published by the EPA documented few concerns about the safety of atrazine herbicides. Based on recommendations from the Scientific Advisory Panel, the EPA reclassified atrazine as “not likely to be a human carcinogen.” A 60-day public comment period followed during which comments from the ag industry, farmers, scientists and activists were collected.
September 26, 2001 EPA Preliminary Ecological Risk Assessment published. The Preliminary Ecological Risk Assessment published by the EPA documented few significant concerns about the safety of atrazine herbicides. A 60-day comment period followed in which both supporting comments from the agriculture industry and concerns from environmental groups were collected.
April 16, 2002 EPA Technical Briefing. This public forum, in which EPA scientists presented their revised risk assessments for atrazine herbicides, began a final, 60-day public comment period on atrazine risk assessments. EPA’s favorable reviews become the basis of the Interim Reregistration Eligibility Decision (IRED).
July 5, 2002 Public comment period on risk assessment ends. EPA receives final comments/input on the risk assessments and drafts the Interim Reregistration Eligibility Decision.
August 3, 2002 Original publication date for Interim Registration Eligibility Document. EPA delayed the atrazine IRED, citing inadequate resources to allow it to meet the August 3, 2002, deadline.
January 31, 2003 EPA completes IRED and briefs manufacturers and stakeholders on content. EPA outlines recommendations in the forthcoming IRED, including increased monitoring and continued stewardship of watersheds in areas where atrazine is used most.
February 28, 2003 IRED is published for 60-day public comment in the Federal Register. The IRED signifies completion of the human health aggregate risk assessment for atrazine current uses and ecological risk assessment (except as noted below).
June 17-20, 2003 EPA Scientific Advisory Panel (SAP) meeting. External panel evaluated the issue of potential effects of atrazine on amphibians. No conclusive evidence. Guidelines established for future research.
July 17, 2003 EPA SAP meeting External panel considers epidemiological data for atrazine and cancer. PSA screening bias plays key role.
October 31, 2003 Amended IRED released. Revised IRED contains results and recommendations from the June 2003 and July 2003 SAP meetings; gives green light for atrazine re-registration.
June 21, 2006 Triazine Cumulative Risk Assessment released. EPA states that the cumulative risks associated with triazine herbicides pose “no harm that would result to the general US population, infants, children or other … consumers.” All tolerances meet the safety standard.
September 21, 2007 EPA issues white paper on latest amphibian research, conducted using EPA-approved protocol. EPA states: “Based on the negative results of these studies, the Agency concludes that it is reasonable to reject the hypothesis formulated in the 2003 SAP that atrazine exposure can affect amphibian gonadal development. The Agency believes at this time, there is no compelling reason to pursue additional testing with regard to the potential effects of atrazine on amphibian gonadal development.”
October 2007 FIFRA Scientific Advisory Panel meeting Independent SAP meets to review/comment on the latest atrazine research on amphibians.
December 2007 FIFRA Scientific Advisory Panel meeting Independent SAP meets to review/comment on the atrazine ecological monitoring program.


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