ABSTRACT
This chapter argues that a high percentage of all chemicals, natural or synthetic, will be rodent carcinogens because testing chemicals—whether mutagens or nonmutagens—at the maximum tolerated dose induces chronic cell proliferation. Cell proliferation is by far the most effective way to convert a heterozygous mutation to homozygosity or hemizygosity through nondisjunction and induction of mitotic recombination. Both DNA damage and cell proliferation are important aspects of carcinogenesis and agents that increase either are proper carcinogens. The levels of the known natural carcinogens in some plants are commonly thousands of times higher than the levels of man-made pesticides. The carcinogens safrole and es-tragole, and a number of related dietary natural pesticides that have not been tested in animal cancer tests, have been shown to give DNA adducts in mice. Epidemiologists are constantly finding clues as to the dietary, viral, and hormonal risk factors for the different types of human cancer.
