APPENDIX II-BG: Pesticide “Inert” Ingredients, PAN

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Pesticide Action Network Pesticide Database







What is a pesticide?

Broadly defined, a pesticide is any agent used to kill or control any pest (1, 2). Pests can be insects, rodents or birds, unwanted plants (weeds), fungi, or microorganisms such as bacteria and viruses. Though often misunderstood to refer only to insecticides, the term pesticide also applies to herbicides, fungicides, microbiocides, rodenticides and various other substances used to control pests. Under United States law, a pesticide is also any substance or mixture of substances intended for use as a insect or plant growth regulator, insect mating disruptor or egg sterilant, defoliant, or desiccant. Many household products are pesticides, such as cockroach sprays and baits, rat poisons, pet flea collars, products that kill mold and mildew, and kitchen disinfectants.

pesticides bulletDefinition of Terms
More About "Inert" Ingredients

Definition of Terms

In evaluating pesticide information, several distinctions associated with pesticides are quite important.

  • Active ingredients are the specific chemicals contained in a pesticide product that are designed to kill a particular pest. By law, the active ingredient must be identified by name on the label together with its percentage by weight.
  • "Inert" ingredients are commonly mixed with the active ingredients to create a formulated pesticide product. See below for more information on "inert" ingredients.
  • Formulated pesticide products are the form of the pesticide that is available to the consumer, grower, or pest control applicator, and may take the form of sprays, bait stations, fly strips, flea collars, dusts, etc.

More About "Inert" Ingredients

Inert ingredients include solvents, emulsifiers, spreaders, and other substances mixed into pesticide products to increase the effectiveness of the active ingredients, make the product easier to apply, or to allow several active ingredients to mix in one solution. An inert ingredient is simply any ingredient in the product that is not intended to affect a target pest (3). Inert ingredients can be as much as 99% of pesticide products. Both U.S. EPA and California Department of Pesticide Regulation require pesticide manufacturers to identify inert ingredients in their products but do not disclose this information to the general public because the pesticide industry considers product formulations trade secrets, protected by law.

Many inert ingredients have adverse health effects and may themselves be used as pesticides. In fact, at least 382 chemicals on the U.S. EPA list of pesticide inert ingredients are or were once registered as pesticide active ingredients (4). Eight inert ingredients are considered by U.S. EPA to be "of toxicological concern" and another 75 are "potentially toxic." The U.S. EPA strongly encourages registrants (manufacturers and companies who buy and repackage pesticides for market) to substitute less toxic substances for these hazardous inerts in pesticide products. Nevertheless, a large but unknown quantity remain in use (5).

While the identity of specific "inerts" in a particular pesticide product is not available to the public, it is possible to estimate the quantity of inert ingredients released into the environment using California Pesticide Use Reporting (PUR) data. In 1998, a total of 215 million pounds of pesticide active ingredients and 134 million pounds of inert ingredients were applied in California. Pesticide products used in urban areas typically contain more inerts than agricultural-use pesticides.

The Northwest Coalition for Alternatives to Pesticides has an extensive web site on "inert" ingredients and their campaign to make them public (6).


  1. What is a Pesticide?, U.S. EPA. Viewed on April 8, 2005.
  2. What is a Pesticide?, California Department of Pesticide Regulation. Viewed on April 8, 2005.
  3. Other Ingredients in Pesticide Products, U.S. EPA. Viewed on April 8, 2005.
  4. S. Marquardt, C. Cox, and H. Knight, Toxic Secrets: "Inert" Ingredients in Pesticides 1987-1997, Northwest Coalition for Alternatives to Pesticides and Californians for Pesticide Reform (San Francisco, 1998). Viewed on April 8, 2005.
  5. List of Other (Inert) Pesticide Ingredients, U.S. EPA. Viewed on April 8, 2005.
  6. Inerts Disclosure Campaign, Northwest Coalition for Alternatives to Pesticides web site. Viewed on April 8, 2005.

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Last updated April 7, 2005 .  



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