Health risk assessment.

In the United States the hazards posed by chemicals are often enormously exaggerated. In "calculating" risks of human cancer and establishing regulations, the United States Environmental Protection Agency makes a series of "conservative" assumptions that have no sound scientific basis. In consequence, trillions of dollars could be wasted. Exaggerations of risks are inherent in the procedures by which rodents are employed as stand-ins for humans. Dependence on results of maximum tolerated doses in the most sensitive strain or species of rodent is questionable. Important examples involve B6C3F1 mice, which in contrast to humans in developed countries, have a high control incidence of liver cancer. Those mice often respond with liver tumors when exposed to large doses of a substance. Other rodents are less often affected. Questionable assessments involving liver cancer in B6C3F1 mice include the risks posed by trichloroethylene, perchloroethylene, methylene chloride, butadiene, and phenobarbital. Spurious assessments for humans have also been noted when the male rat was the most sensitive animal. A unique mechanism in them gives rise to kidney tumors while female rats and male and female mice are not affected.