ABSTRACT
The regulation of exposure to chemicals, including the intermittent exposure to trace elements to which the general public is subject, is largely based on interpretations of animal cancer bioassays. If these tests are reasonably accurate in predicting the probability, sites, and severity of human cancers, then regulation of chemicals suspected of causing cancer (carcinogens) is on firm ground. Animal studies have many important uses. Research into cancer mechanisms or problems of the immune system, for instance, may be furthered by introducing novel genes into small animals, such as transgenic mice, to discover better how life systems work. Knowledge of mechanisms yields far greater discriminatory power. In the field of pesticide regulation, lethality is calculated through the assignment of an LD50, the lethal dose for one-half of the test animals during the test period. The larger the LD50, the more of a substance it takes to produce a toxic effect and the less harmful the chemical.
