Animal carcinogen testing challenged.

The past 15 years have seen a long list of man-made chemicals indicated as potential human carcinogens. Now, a prominent cancer researcher says that the risks of those chemicals have been overestimated partly because of a serious design flaw in the animal tests used to assess their carcinogenicity. The researcher, Bruce Ames of the University of California, Berkeley, has become well known for his views that many of the newsmaking carcinogens pose little risk to the general human population. He also argues that current policies for testing and regulating carcinogens, which emphasize synthetic chemicals, are misdirected. In animal tests the chemicals are usually administered in the maximum tolerated doses (MTDs), which are the highest doses that can be given without causing severe weight loss or other life-threatening signs of toxicity. Even though these levels are much higher than the doses to which people are likely to be exposed, MTDs are used to cut down on the number of animals- and thus the cost-required to obtain statistically significant results. Although the MTDs don't cause overt signs of toxicity, they can still have more subtle toxic effects, however, and that is what Ames thinks accounts for the large number of compounds thatmore » test positive for carcinogenicity.« less