Atrazine
Atrazine is a chlorinated triazine systemic herbicide that is used to selectively control annual grasses and broadleaf weeds before they emerge. Pesticide products containing atrazine are registered for use on several agricultural crops, with the highest use on field corn, sweet corn, sorghum, and sugarcane. Additionally, atrazine products are registered for use on wheat, macadamia nuts, and guava, as well as non-agricultural uses such as nursery/ornamental and turf.
EPA's oversight of atrazine is dynamic and includes periodic re-evaluation through the registration review process. Over the years, EPA has consulted with the FIFRA Scientific Advisory Panel (SAP) on a variety of atrazine topics.
- Registration review of atrazine
- Atrazine ecological exposure monitoring program
- Triazine registration review
- Triazine cumulative human health risk assessment
- Triazine ecological risk assessments
- FIFRA Scientific Advisory Panel Meetings on Atrazine
Registration Review of Atrazine
The Federal Insecticide, Fungicide and Rodenticide Act (FIFRA) requires EPA to review each registered pesticide at least every 15 years to ensure that each pesticide can carry out its intended function(s) without creating unreasonable adverse effects to human health and the environment and to ensure that risk assessments and pesticide decisions reflect the best available science. All documents related to the registration review for atrazine can be found in the atrazine registration review docket EPA-HQ-OPP-2013-0266 at www.regulations.gov.
In September 2020, EPA released the Interim Registration Review Decision for atrazine, finalizing mitigation measures to protect human health and mitigate potential ecological risks. EPA completes interim registration review decisions to identify interim risk mitigation measures necessary to protect human health and the environment, while the Agency conducts other longer-term assessments, such as the endangered species assessment. Labels implementing the mitigation identified in the September 2020 interim decision (ID) were stamped and approved in November 2021.
In November 2021, EPA released the final Biological Evaluation (BE) assessing risks to listed species from labeled uses of atrazine. EPA solicited public comments on the draft BE for atrazine, which was released in November 2020, and prepared a response to comments document. EPA is in consultation with the U.S. Fish and Wildlife Service and the National Marine Fisheries Service.
June 2022 Updates
In October 2020, EPA was sued alleging that the agency violated its duties under FIFRA when it issued the atrazine ID. In August 2021, EPA sought a voluntary partial remand in light of President Biden’s executive order on protecting public health and the environment and restoring a commitment to science and scientific integrity. On December 14, 2021, the Ninth Circuit Court of Appeals granted EPA a voluntary partial remand, which provided the agency the opportunity to reevaluate the policy decision to use 15 μg/L as the level of regulation for aquatic plant communities.
Based on its review of the substantial evidence associated with the atrazine ecological risk assessment and a consideration of growers’ need for flexible and manageable mitigation measures, EPA proposed and received public comment on additional mitigation to protect aquatic plant communities. EPA proposed the following measures for all atrazine labels in order to decrease atrazine runoff from treated fields:
- Prohibit application when soils are saturated or above field capacity (i.e., the soil’s ability to retain water);
- Prohibit application during rain or when a storm event, likely to produce runoff from the treated area, is forecasted to occur within 48 hours following application;
- Prohibit aerial applications of all formulations;
- Restrict annual application rates to 2 pounds of active ingredient or less per acre per year or less for applications to sorghum, field corn, and sweet corn.
In addition to the measures listed above, EPA proposed to add a “picklist” to labels that would require growers to select a combination of application rate reductions and/or runoff control measures to further mitigate potential risks to aquatic plant communities. The number of runoff control practices from the picklist that a grower would be required to implement depended on the estimated atrazine concentration in the watershed where the field is located and that watershed’s vulnerability to atrazine runoff, as well as the grower’s selected application rate. The higher the application rate and the higher the estimated atrazine concentration in the watershed, the greater the number of mitigation practices that may be necessary.
The picklist approach would provide growers with the flexibility to select the runoff control practices that would be least burdensome to adopt. The practices a grower selects may depend on a variety of factors including crop, geographic region, and field topography. The picklist mitigation requirements were tailored geographically, down to the watershed level, in order to focus the mitigation on the areas with the greatest risk and vulnerability.
EPA accepted public comment on the proposed revisions to the atrazine ID for 90 days.
August 2023 SAP Meeting
In August 2023, EPA convened a meeting of the Federal Insecticide, Fungicide, and Rodenticide Act Scientific Advisory Panel (SAP) to evaluate eleven studies and their associated publications, which EPA had used to calculate its science-based concentration-equivalent level of concern (CE-LOC) for atrazine of 3.4 µg/L. The CE-LOC is the concentration of atrazine in water above which EPA expects there to be adverse effects to aquatic plant communities. The SAP is a forum that provides independent scientific advice and recommendations on scientific issues related to pesticides. After the SAP, EPA reevaluated two additional relevant studies based on public comments and letters to the Agency requesting reexamination.
July 2024 Updates
In July 2024, EPA announced an update to the level at which atrazine is expected to adversely affect aquatic plants. The new revised atrazine concentration of 9.7 micrograms per liter (µg/L), which was derived following an August 2023 peer review, will be used to develop a revised regulatory decision to help protect aquatic plants as well as fish, invertebrates, and amphibians.
The level at which atrazine is expected to adversely affect aquatic plants is also known as the concentration-equivalent level of concern or CE-LOC. Included in the announcement is an EPA memorandum that provides details on updates to EPA’s database of aquatic plant community studies and revised exposure modeling. Also included is an updated map that shows where the level of concern is expected to be exceeded. Collectively, these updates resulted in the removal of millions of acres of land from the 2022 map of watersheds that were expected to exceed the level of concern and added a much smaller number of acres in other areas of the country. Later this year, EPA plans to update its 2022 atrazine mitigation proposal to reflect the revised level of concern and the corrections to the exposure modeling, as well as to incorporate feedback received during the 2022 public comment period. EPA will take public comment on the revised mitigation proposal and also release a response to comments on the 2022 proposed revisions to the interim decision at that time.
More information on the registration review process is available here.
Additional information on atrazine’s registration review and reregistration is available in the atrazine dockets at www.regulations.gov:
| Docket ID | Docket Title |
|---|---|
| EPA-HQ-OPP-2003-0367 | Atrazine Interim Reregistration Eligibility Decision |
| EPA-HQ-OPP-2013-0266 | Atrazine Registration Review |
| EPA-HQ-OPP-2013-0266-0008 | Preliminary Work Plan |
| EPA-HQ-OPP-2013-0266-0308 | Final Work Plan |
| EPA-HQ-OPP-2013-0266-0315 | Refined Ecological Risk Assessment for Atrazine |
| EPA-HQ-OPP-2013-0266-1159 | Atrazine Draft Human Health Risk Assessment for Registration Review |
| EPA-HQ-OPP-2013-0266-1274 | Atrazine Proposed Interim Decision |
| EPA-HQ-OPP-2013-0266-1605 | Atrazine Interim Decision |
| EPA-HQ-OPP-2013-0266-1625 | Proposed Revisions to the Atrazine Interim Registration Review Decision |
| EPA-HQ-OPP-2013-0266-1623 |
EFED Support Documentation for the Proposed Revisions to the Atrazine Interim Registration Review Decision Regarding Risks to Aquatic Plant Communities |
| EPA-HQ-OPP-2013-0266-1624 | Assessment of the Benefits of Atrazine and the Impacts of Potential Mitigation for Field Corn, Sweet Corn, Sorghum, and Sugarcane |
| EPA-HQ-OPP-2013-0266-2128 | Update to “EFED Support Documentation for the Proposed Revisions to the Atrazine Interim Registration Review Decision Regarding Risks to Aquatic Plant Communities” |
| EPA-HQ-OPP-2013-0266-2129 | High resolution map of HUC 12 watersheds that exceed the updated CE-LOC for atrazine |
Atrazine Ecological Exposure Monitoring Program
The Atrazine Ecological Exposure Monitoring Program (AEEMP) assesses atrazine levels in streams in watersheds that are exposed to atrazine runoff from corn and sorghum production (small streams, high atrazine use areas, and vulnerable soils). This monitoring program is required by the 2003 Atrazine Interim Reregistration Eligibility Decision and the 2004 Atrazine Memorandum of Agreement.
- 2006 Atrazine Interim Reregistration Eligibility Decision (pdf). This document contains the January 2003 IRED and October 2003 revised IRED.
- Memorandum of Agreement with registrants (2004) (pdf).
View Atrazine Ecological Exposure Monitoring Program Data and Results
Triazine Registration Review
Atrazine is chemically related to two other herbicides, simazine and propazine , which together are called "triazines." The triazines have a common mechanism of toxicity, and therefore EPA conducted both individual chemical and cumulative human health risk assessments.
Interim Registration Review Decision
In September 2020, EPA released the triazine (atrazine, propazine, and simazine) interim decisions. In June 2022, EPA released for public comment the proposed revisions to the atrazine interim decision. In June 2022, EPA released for public comment the Proposed Revisions to the Atrazine Interim Registration Review Decision. After considering comments on the proposed revisions, EPA will proceed with a revised interim decision for atrazine.
- Read the atrazine interim decision.
- Read the proposed revisions to the atrazine interim decision.
- Read the propazine interim decision.
- Read the simazine interim decision.
Triazine Cumulative Human Health Risk Assessment
In July 2018, as part of EPA’s registration review process, the Agency released the cumulative human health risk assessment for the triazines. In addition to the cumulative human health risk assessment, EPA also released atrazine, simazine, and propazine human health risk assessments.
- Read the cumulative human health risk assessment.
- Note: the cumulative assessment can be found in all triazine dockets
- Read the atrazine human health risk assessment.
- Read the simazine human health risk assessment.
- Read the propazine human health risk assessment.
In the cumulative assessment, EPA reviewed all available scientific data, including published toxicity and epidemiology literature. EPA’s assessment found no risks of concern when evaluating all dietary exposure sources including drinking water.
The assessment identified potential risks to:
- children who crawl and play on lawns treated with atrazine or simazine and
- workers who mix, load, and apply atrazine.
The September 2020 interim registration review decisions identified mitigation to address these risks of concern, and product labels including these mitigations were stamped and approved in November 2021.
Triazine Ecological Risk Assessments
In 2016, EPA released the draft ecological risk assessments for atrazine, simazine, and propazine, which evaluate risks to animals and plants, including amphibians, birds, mammals, fish, reptiles, aquatic invertebrates, aquatic plant communities, and terrestrial plants. For ecological risks, each of the triazines (atrazine, propazine, and simazine) was assessed separately.
- View the Federal Register Notice.
- Find the triazine ecological risk assessments.
- View the Atrazine Regulatory Update Memo (October 2019), regarding the Community Effects Level of Concern (CE-LOC) for regulating aquatic plants.
FIFRA Scientific Advisory Panel Meetings on Atrazine
The Agency has consulted with the FIFRA Scientific Advisory Panel on 12 occasions on various topics regarding the evaluation of atrazine data and key aspects of its risk assessments since 2000, all of which are listed in the table below. The FIFRA SAP is composed of independent scientists who advise on technically challenging scientific assessment issues.
Meeting materials and summaries are available on the FIFRA Scientific Advisory Panel website or in www.regulations.gov (search by the Docket number).
| Meeting Title | Docket Number | Date |
|---|---|---|
| Examination of Mesocosm and Microcosm Studies for Evaluating the Effects of Atrazine on Aquatic Plant Communities | EPA-HQ-OPP-2023-0154 | 8/22-23/2023 |
| Problem Formulation for Reassessment of Ecological Risks from Use of Atrazine | EPA-HQ-OPP-2012-0230 | 6/12-15/2012 |
| Re-Evaluation of Human Health Effects of Atrazine: Review of Non-Cancer Effects, Drinking Water Monitoring Frequency, and Cancer Epidemiology | EPA-HQ-OPP-2011-0399 | 7/26-29/2011 |
| Re-Evaluation of Human Health Effects of Atrazine: Review of Non-Cancer Effects and Drinking Water Monitoring Frequency | EPA-HQ-OPP-2010-0481 | 9/14-17/2010 |
| Re-Evaluation of Human Health Effects of Atrazine: Review of Experimental Animal and In Vitro Studies and Drinking Water Monitoring Frequency | EPA-HQ-OPP-2010-0125 | 4/26-29/2010 |
| Draft Framework and Case Studies on Atrazine, Human Incidents, and the Agricultural Health Study: Incorporation of Epidemiology and Human Incident Data into Human Health Risk Assessment | EPA-HQ-OPP-2009-0851 | 2/2-5/2010 |
| Presentation of the Atrazine Reevaluation Plan | EPA-HQ-OPP-2009-0759 | 11/3/2009 |
| Ecological Significance of Atrazine Effects on Primary Producers in Surface Water Streams in the Corn and Sorghum Growing Region of the United States | EPA-HQ-OPP-2009-0104 | 5/12-15/2009 |
| Interpretation of the Ecological Significance of Atrazine Stream-Water Concentrations Using a Statistically-Designed Monitoring Program | EPA-HQ-OPP-2007-0934 | 12/4-7/2007 |
| Potential for Atrazine to Affect Amphibian Gonadal Development | EPA-HQ-OPP-2007-0498 | 10/9-12/2007 |
| Characterization of Epidemiology Data Related to Prostate Cancer and Exposure to Atrazine | EPA-HQ-OPP-2003-0186 | 7/17-18/2003 |
| Potential Developmental Effects of Atrazine on Amphibians | EPA-HQ-OPP-2003-0024 | 6/17-20/2003 |