EPA Posts for Public Comment Examination of Microcosm/Mesocosm Studies for Evaluating the Effects of Atrazine on Aquatic Plant Communities

This original announcement was published by the EPA on July 3, 2023, Click here for more information.


The U.S. Environmental Protection Agency (EPA) is seeking public comment on the white paper Examination of Microcosm/Mesocosm Studies for Evaluating the Effects of Atrazine on Aquatic Plant Communities. These studies are part of EPA’s Ecological Risk Assessment of the herbicide atrazine and are specifically used in assessing the effects to aquatic plant communities. The white paper presents EPA’s reevaluation of 11 atrazine microcosm and mesocosm (‘cosm’) studies identified by the 2012 Federal Insecticide, Fungicide and Rodenticide (FIFRA) Scientific Advisory Panel (SAP) as warranting further review. The reevaluation is being submitted for peer review to the Federal Insecticide, Fungicide, and Rodenticide Act Scientific Advisory Panel (FIFRA SAP) which provides EPA with independent scientific advice and recommendations on health and safety issues related to pesticides.

Atrazine is an herbicide used to control annual broadleaf and grass weeds. It is primarily used on corn, sorghum, and sugarcane crops, but is registered for a wide variety of uses including wheat, macadamia nuts, guava, soybeans, fallow crop lands, and non-agricultural use sites (e.g., turfgrass).

Aquatic plant communities are vital to aquatic and terrestrial food webs and ecosystems; therefore, changes to these communities could alter the functioning of the ecosystem. EPA evaluated the toxicity of atrazine to aquatic plant communities using cosm studies, which are useful tools in understanding complex community interactions under semi-controlled conditions.

Overall, EPA is proposing changes to the database of cosm studies used for analysis; specifically, excluding some studies and endpoints, while adding or adjusting other endpoints. The FIFRA SAP’s feedback on EPA’s 2023 reevaluation and revised conclusions regarding these studies will inform how EPA ultimately uses these 11 cosm studies in the determination of the atrazine level of concern in aquatic environments.

Upon publication, the document is available for public comment in docket EPA-HQ-OPP-2023-0154 at for 30 days. Comments will be considered by the FIFRA SAP in peer review. When submitting comments, follow the online instructions. Do not electronically submit any information you consider to be confidential business information or other information where disclosure is restricted by statute. Copyrighted material will not be posted without explicit permission of the copyright holder. Members of the public should also be aware that personal contact information, if included in any written comments, may be posted on the internet.

Virtual Public Meeting

The FIFRA SAP will review the reevaluation document at a 3-day virtual public meeting on August 22-24, 2023, from 10:00 a.m. to approximately 5:30 p.m. EDT. The meeting will include the examination of 11 microcosm/mesocosm studies used in evaluating the effects of atrazine on aquatic plant communities and consideration of public comments. Registration information for the meeting will be announced on the FIFRA SAP website later in July.

For additional information, please contact the Designated Federal Official, Tamue Gibson, at or 202-564-7642.