Under the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA), all pesticides sold or distributed in the United States must be registered with EPA. Because of concern that some inert ingredients might also cause adverse effects to humans and the environment, EPA outlined its strategy for regulating inert ingredients in 1987. EPA categorized inert ingredients into four toxicological categories; List 1-Inerts of toxicological concern, List 2-Potentially toxic inerts/high priority for testing, List 3-Inerts of unknown toxicity, and List 4-Inerts of minimal concern. In 1989, EPA subdivided List 4 into two lists. List 4 became List 4A, representing minimal risk inert ingredients. List 4B was created to represent inert ingredients for which EPA had sufficient data to conclude that their current use patterns in pesticide products will not adversely affect the environment. Substances without Chemical Abstracts Service (CAS) Registry Numbers have not been added to the Chemical Registry.