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Minimum Risk Pesticides: Permitted Inerts

In addition to active ingredients from the approved 25(b) list, federal regulations state that minimum risk pesticides may only contain the minimal risk inert ingredients noted in List 4A. Minimum risk pesticide producers may use List 4A inert ingredients in whatever amounts they believe will result in an effective product when combined with 25(b) active ingredients. Inert ingredients are defined as all ingredients that are not active ingredients. Active ingredients are the ingredients that kill, repel, or mitigate the pest.

EPA’s determination that an inert ingredient poses minimal risk is based on the following:

Minimum risk pesticide labels must include the name of each inert ingredient, as well as listing the name and percentage by weight of active pesticidal ingredients.

Can a chemical be an inert ingredient in one pesticide product and an active ingredient in another?

It is possible for a chemical to be an inert ingredient in one pesticide product and an active ingredient in another pesticide product. Minimum risk pesticide manufacturers must be extremely careful to never use an inert ingredient from List 4A as an active ingredient unless the ingredient is also on the 25(b) active ingredient list.


Citric acid and several essential oils are examples of minimum risk pesticide ingredients that can be found on both the 25(b) active ingredient list and List 4A.

Vinegar is a good example of a minimum risk inert ingredient that can pose a hazard if improperly and illegally used as an active ingredient in an unregulated 25(b) pesticide product. EPA added vinegar (maximum of 8% acetic acid in solution) to List 4A to give manufacturers a safe means of controlling pH in minimum risk pesticide products.

When used as an inert ingredient to buffer pH, the quantity of vinegar in a pesticide product is not expected to pose hazards. However, vinegar with an acetic acid concentration greater than 8% is a potent herbicide and at higher concentrations can cause severe burns.

Because of this potential safety concern, vinegar is not listed as a minimum risk active ingredient and may not be used as an active ingredient in unregistered, minimum risk pesticides. The same is true of any List 4A inert that coincidentally has some sort of pesticidal property: if it is not on the 25(b) active ingredient list, it may not be used as an active ingredient in minimum risk pesticides.

Enforcement actions can result from violations of federal pesticide law

Minimum risk pesticide manufacturers sometimes market pesticides in which List 4A inert ingredients act as active ingredients in the product formulation even though they are listed as inerts on the label. The Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) gives EPA the authority to take enforcement action if the purpose or intent of a minimum risk pesticide inert ingredient is to act as an active ingredient.

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