Proposed EPA Rule to Limit Use of Atrazine

Last month, the EPA issued a proposed rule that would limit the use of atrazine. Atrazine is a common herbicide that is used to stop pre and post emergence broadleaf and grassy weeds in crops such as sorghum and corn. It is the second most widely used herbicide after glyphosate. Studies, including a 2007 study from the International Journal of Occupational and Environmental Health, and a 2017 study from Weed Science, estimate that positive effect on corn yields have been anywhere from 1-8%. A 2014 article from Pest Management Science estimates that the positive effects on sorghum yields have been as high as 20%.

The proposed rules involve a level of aquatic level concentration of 3.4 parts per billion, as opposed to the current 15 parts per billion. The Missouri Farm Bureau has protested the new rules, saying these rules would dramatically impact atrazine use for over 70% of corn acres nationwide. They say that the EPA did not convene a Scientific Advisory Panel in making this decision, and that previous panels dismissed such a low level.

In the event of watersheds with concentrations exceeding 3.4 parts per billion, the EPA would recommend a combination of reduced application rates and runoff control measures, which the Farm Bureau says would also affect 90 other herbicide formulations. They say the estimated cost to replace atrazine would be $42 per acre due to replacement costs and yield loss due to decreased pest control

In September 2020, the Trump Administration announced it would be reapproving atrazine for the next 15 years. The Center for Biological Diversity and other public interest groups sued, saying the Trump Administration disregarded safeguards for children’s health, allowed more than 50% more atrazine to end up in US waterways, ignored recommendations from the National Academy of Sciences, and violated the Endangered Species Act. 

In November 2020, as the result of a court settlement, the EPA released an assessment finding that atrazine is likely to harm more than 1,000 of the nation’s endangered plants and animals. 

In November 2021, a followup assessment conducted by the EPA included a 64 page document describing the harmful effects of atrazine on plants, fish, birds, and mammals. The introduction reads in part, “In target pests (e.g., various weed species), atrazine has a mechanism of action of inhibiting photosynthesis in photosystem II (PSII). Triazine herbicides such as propazine bind with a protein complex of the Photosystem II in chloroplast photosynthetic membranes (Schulz et al., 1990). The result is an inhibition in the transfer of electrons through the light reactions of photosynthesis that in turn inhibits the formation and release of oxygen, production of adenosine triphosphate, and the fixation of carbon dioxide into sugars.”

“Atrazine is slightly toxic to birds and mammals and is practically non-toxic to terrestrial invertebrates on an acute exposure basis. In most terrestrial animal species, chronic effects are the predominant concern and are discussed further below. Based on the mechanism of action in target plants, i.e., disruption of photosynthesis, atrazine is toxic to most photoautotroph organisms including unicellular algae and flowering plants.”

“Atrazine is moderately toxic to freshwater and estuarine/marine fish, highly toxic to freshwater aquatic invertebrates and very highly toxic to estuarine/marine aquatic invertebrates on an acute exposure basis. Chronic exposure studies for freshwater and estuarine/marine fish, aquatic phase amphibians and aquatic invertebrates resulted in effects on survival, growth or reproduction.”

The EPA is accepting public comments on the proposed rule until October 7th.


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