EPA Announces Update on Atrazine

United States Environmental Protection Agency

EPA Announces Update on Atrazine

The U.S. Environmental Protection Agency (EPA) is announcing 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 on the degree at which atrazine affects 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 this 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.

In its 2016 atrazine ecological risk assessment, EPA determined that the scientifically derived level of atrazine, measured as a 60-day average, that negatively impacted the aquatic environment was 3.4 µg/L.

Since that time, questions about the scientific integrity of the assessment of atrazine were raised after the previous administration directed career managers to exclude studies related to the effects of atrazine from being used as a basis for ecological risk management.

In September 2020, EPA set a less protective level for atrazine at 15 µg/L.

The following month, EPA received a lawsuit alleging that the Agency violated its duties under the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) by making its Atrazine Interim Registration Review Decision without substantial supporting evidence. In August 2021, EPA sought a voluntary partial remand and on December 14, 2021, the Ninth Circuit Court of Appeals granted that remand, which provided the agency the opportunity to reevaluate it.

In August 2023, the Agency convened a meeting of the FIFRA Scientific Advisory Panel (SAP) to evaluate eleven studies and their associated publications, which EPA had used to calculate its science-based level of concern for atrazine of 3.4 µg/L. The SAP is a forum that provides independent scientific advice and recommendations on scientific issues related to pesticides. After the SAP, EPA also reevaluated two additional relevant studies based on public comments and letters to the Agency requesting reexamination. After indicating concurrence with the recommendations received from the SAP and taking into consideration its reevaluation of the additional two studies, EPA has recalculated the level of concern for atrazine as 9.7 µg/L as a 60-day average.

For additional information, please visit docket EPA-HQ-OPP-2013-0266 at www.regulations.gov.