US EPA releases updated mitigation proposal for atrazine

On December 3, the U.S. Environmental Protection Agency (EPA) is proposing updated mitigation measures for the pesticide atrazine. This proposal contains mitigation measures to reduce exposure to non-target species and minimize impacts to federally endangered and threatened (listed) species and their designated critical habitats. The updated mitigation proposal also incorporates the revised level at which atrazine is expected to adversely affect aquatic plant communities, an expanded use of robust surface water monitoring data, as well as the runoff mitigation menu and point system from the Final Herbicide Strategy. 

EPA developed the mitigation menu to provide growers with the flexibility to use mitigations that are most appropriate for their field situations. The mitigation menu was recently updated to include additional options to achieve mitigation points and reduce runoff. This updated mitigation proposal for atrazine also includes EPA’s response to public comments received on its 2022 proposal.

Background

Atrazine is one of the most widely used herbicides in the United States. It is used to control annual broadleaf and grass weeds in a variety of agricultural crops, primarily corn, sorghum, and sugarcane. Atrazine products are also registered for numerous other uses including macadamia nuts, guava, fallow crop lands, and turfgrass.

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. If potential risks are identified as unreasonable, then EPA determines if additional mitigation measures can be implemented to reduce those risks.

As part of the atrazine ecological risk assessment, a concentration-equivalent level of concern or CE-LOC is established, which is the concentration of atrazine in water that is expected to adversely affect aquatic plant communities. In the 2016 atrazine ecological risk assessment, EPA determined that the scientifically derived CE-LOC was 3.4 µg/L, measured as a 60-day average. However, in September 2020, a less protective level for determining the need for mitigation at 15 µg/L was set that was based on a policy decision rather than a scientific one and raised questions about scientific integrity. Following subsequent litigation and partial remand of its 2020 Atrazine Interim Registration Review Decision, in 2022, EPA released a proposal for updated mitigation to address atrazine runoff and mitigate risks to aquatic plant communities, which was based on the CE-LOC of 3.4 µg/L. Since that time, the agency convened a meeting of the FIFRA Scientific Advisory Panel (SAP) to evaluate studies that were used to calculate the atrazine CE-LOC. Following the SAP, EPA reevaluated two additional relevant studies based on public comments and letters to the agency, which resulted in recalculating the CE-LOC for atrazine as 9.7 µg/L.

Since the release of the 2022 atrazine mitigation proposal, EPA also finalized its Herbicide Strategy to protect federally endangered and threatened (listed) species from potential impacts of herbicides. The final strategy was released in August 2024 and was applied during the development of the updated mitigation proposal for atrazine. The final strategy reflects many improvements, additional ways to comply and other increases in flexibility that were made by EPA based on the extensive comments from stakeholders and the public.

Updated Atrazine Mitigation Proposal

EPA’s approach is targeted to provide maximum flexibility (recognizing atrazine’s high benefits) while addressing the need for mitigation. EPA has identified watersheds that exceed the revised CE-LOC of 9.7 µg/L through analysis of modeling data in combination with available water monitoring data. Under the updated proposal, EPA determined that a field located in a watershed with a predicted atrazine concentration above the CE-LOC of 9.7 ug/L but below 45.4 µg/L would need to achieve three points of mitigation. For a field located in a watershed with a predicted concentration at or above 45.4 µg/L, EPA identified six points of mitigation to be necessary. The specific mitigation measures that may be used to achieve the required points are described in the Herbicide Strategy’s mitigation menu. Using the mitigation menu and point system also reduces the level of mitigation needed for applicators who have already implemented measures to reduce pesticide runoff from a field such as conservation tillage or grass waterways. Growers who already use those measures may not need any additional runoff measures.

In addition to the mitigation points, EPA is proposing several nationwide runoff reduction measures identified as necessary for all atrazine labels, including prohibiting application during rain or when soils are saturated or above field capacity, and annual application rate reductions.

Upon publication in the Federal Register, the Updated Mitigation Proposal for the Atrazine Interim Registration Review Decision, along with all atrazine registration review documents, will be available in docket EPA-HQ-OPP-2013-0266 at www.regulations.gov for public comment for 60 days. EPA will continue to keep the public updated as it evaluates and takes any actions related to atrazine pesticide use. For more information, view a prepublication version of the Federal Register notice, the mitigation proposal and atrazine water concentration maps.