Animal toxicity studies conducted for regulatory submission typically are conducted in rats, mice, rabbits, and dogs with greater focus on rats. Testing guidelines generally require that common laboratory strains be used. At least three dose groups and a control group usually are required. For most toxicity tests, the U.S. Environmental Protection Agency (EPA) requires that the highest dose elicit signs of toxicity without compromising survival. EPA strongly recommends that the lowest dose not produce any evidence of toxicity. The numbers of animals required are defined in each study protocol and range from five rats per sex per dose in 28-day toxicity studies to 10 rats per sex per dose in subchronic studies to 50 rats per sex per dose in carcinogenicity assays. For developmental and reproductive studies, the litter is considered the experimental unit, and at least 20 litters per dose are required. The statistical power of a study is determined by the number of animals used and the sensitivity of the end point being evaluated.
This chapter provides an overview of consensus-study protocols developed or codified by several organizations, including EPA and the Organisation for Economic Co-operation and Development (OECD). EPA specifies the types and extent of toxicity data that it requires to make regulatory decisions regarding the risks and benefits associated with pesticide products in accordance with the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) and the Federal Food, Drug, and Cosmetic Act (FFDCA). The specific data requirements are listed in the Code of Federal Regulations (CFR), Title 40, Subpart E, Part 158 (40CFR158). EPA also requires testing of industrial chemicals under the Toxic Substances Control Act (TSCA). EPA has harmonized the testing protocols that may be used in support of FIFRA registrations and TSCA test rules and has harmonized the guidelines with those of OECD. Appendix B of this report provides a list of EPA’s harmonized health-effects test guidelines.
OECD also develops test guidelines and guidance documents to help to characterize potential hazards associated with new and existing chemicals. The OECD document, Guidelines for the Testing of Chemicals (OECD Guidelines), is a collection of the most relevant internationally agreed-on testing methods used by government, industry, and independent laboratories (OECD 2004a). OECD publishes the guidelines to relieve some of the burden of chemical testing and assessment in multiple countries. Appendix B provides a list of OECD’s health-effects test guidelines.