Chlorpyrifos tolerances revoked by U.S. EPA

Adam Varenhorst
South Dakota State University Extension

In August 2021, a final rule was released by the U.S. Environmental Protection Agency (EPA) for the insecticide active ingredient chlorpyrifos. The rule revoked all tolerances for chlorpyrifos. The tolerances represent the amounts of a pesticide product that are allowed on food while still considered safe. Since all tolerances have been revoked, chlorpyrifos has effectively been removed from the list of insecticides that can be used to manage insect pests in South Dakota crops.

Chlorpyrifos is an active ingredient that belongs to the organophosphate insecticide class (Group 1B). Organophosphates are acetylcholinesterase inhibitors, which means that they work by disrupting a certain part of the insect nervous system. This action leads to the buildup of acetylcholine in the nervous system, which results in overstimulation. While all insecticides should be handled with care, organophosphates can pose serious health hazards if exposure occurs. The human nervous system contains the same parts that chlorpyrifos targets in insects.

The final rule will be effective Oct. 29, 2021, and the tolerances for all commodities will expire on Feb. 28, 2022. At this time, the affected entities include anyone associated with crop production, animal production, food manufacturing and pesticide manufacturing. Chlorpyrifos is also undergoing registration review, which must be completed by Oct. 1, 2022. Any products that have chlorpyrifos residues after Feb. 28, 2022 will still be rendered usable as long as:

Residue that is present was the result of an application of chlorpyrifos that occurred at a time and manner while use was lawful.

Residue does not exceed tolerances that were previously authorized.

Evidence that the products were treated lawfully includes records that verify the dates of application.

Based on the final rule, application of chlorpyrifos in 2022 will result in unlawful residues on crops. For this reason, existing stocks should not be utilized. We will continue to monitor this decision for any changes or clarification of the rule that may affect the use of chlorpyrifos on South Dakota crops.