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Extent of Carcinogenicity Testing of Commercial Chemicals

Knowledge about the extent of carcinogenicity testing is required to characterize future needs and to set priorities for research on potential human carcinogens. An excellent source of information on this topic is a recent study produced by the National Research Council’s (NRC) Board on Toxicology and Environmental Health Hazards, Toxicity Testing: Strategies to Determine Needs and Priorities. This report documents what many have feared: adequate testing is lacking for the vast majority of chemicals for which the potential for human exposure is very high. Although this study is wider in scope, the following material summarizes the findings it contains on carcinogenicity testing of commercial chemicals. The NRC investigated commercial chemicals for two reasons: “(1) To characterize the toxicity-testing needs for substances to which there is known or anticipated human exposure, so that federal agencies responsible for the protection of public health will have the appropriate information needed to anticipate the extent of testing needs. (2) To develop and validate uniformly applicable and wideranging criteria that may be used to set priorities for research on substances with potentially adverse public-health impact.” There are an estimated five million known chemicals. A manageable list of substances with high potentials for human exposure was assembled from computerized databases of commercial chemicals that included the Toxic Substance Control Act Inventory of 48,523 chemical substances in commerce; a list of 3350 active and inert ingredients of pesticides registered by the Environmental Protection Agency; a list of 1815 prescription and nonprescription drugs and excipients approved by the Food and Drug Administration; and a list of 3410 cosmetic ingredients from the Cosmetic, Toiletry and Fragrance Association. A total of 65,725 entries was compiled which, when duplication was taken into account, contained about 53,500 distinct entries. From this original list of substances, an initial random sample of 675 was selected for investigation. These substances were organized into seven categories on the basis of their intended use. A final subsample of 100 chemicals (pesticides, 15; cosmetics, 15; drugs, 15; food additives, 15; chemicals in commerce > million lb/yr, 10; chemicals in commerce < million lb/yr, 10; chemicals in commerce, unknown or inaccessible quantities, 20) was selected for closer analysis from the initial random sample of 675. This selection was made by using the collective expertise of the NRC committee members to establish requirements for the amount and type of toxicity testing that would provide minimal toxicity information for each category of substances. Determinations were made as to which of the 675 substances had defined minimal amounts of toxicity information in the following five classes of toxicity-testing studies: acute, subchronic, chronic, reproductive or developmental, and mutagenicity. The specific classes of toxicity