Inert ingredients in pesticides can consist of 99.80 percent of the product, but haven’t been required to be on the label until now. On December 23rd, 2009, the U.S. Environmental Protection Agency announced that it would require pesticide manufacturers to disclose these ingredients. There are nearly 4,000 inert ingredients used in pesticides, and the chemicals are not actual pesticides but can be very toxic nonetheless. Formaldehyde, bisphenol A, sulfuric acid, toluene, benzene and styrene are among the ingredients that are allowed in pesticides but are not identified on labels. Some are carcinogens, while some may cause reproductive or respiratory problems if people are exposed.
http://www.environmentalhealthnews.org/ehs/news/inert-ingredients-in-pesticides