Spraying for mosquitoes has increasingly become a summer routine in many areas, thanks to the West Nile virus. Residents who want to find out what's being sprayed could turn to the product label on the container. But even a thorough reading of the label won't tell the whole story. Most "inert" ingredients, which often constitute up to 99 percent of the product contents, are not listed. Yet they can be biochemically active--for example, an unlisted ingredient in the mosquito pesticide Dibrom is naphthalene, which might cause cancer and developmental problems in exposed children. Now some activists are trying to get the Environmental Protection Agency to force chemical makers into revealing their hidden compounds.

According to the Federal Insecticide, Fungicide and Rodenticide Act, pesticide ingredients qualify as inert when their function in a product is something other than killing the target pest. For instance, an inert may make a product sticky, or sprayable, or attractive to a particular kind of bug or rodent. Yet the term "inert" does not bear on the toxicity of the ingredient to other organisms.

This article was originally published with the title Secret Ingredients.

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