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标题：Thresholds for Carcinogens: A Review of the Relevant Science and Its Implications for Regulatory Policy
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作者：Wilson, James D.
期刊名称：Journal of Food Distribution Research
印刷版ISSN：0047-245X
出版年度：1996
期号：SUPPL
出版社：Food Distribution Research Society
摘要：Regulation of carcinogens in the United States has been based on a "no threshold" policy. Thismakes the assumption there exists no level of exposure for which the possibility of causing harm is trulyzero. The alternative "threshold" policy assumes that there exists some level of exposure at which noharm will come to anyone in a population so exposed. The no-threshold policy made sense whenadopted, thirty or more years ago, since the science then available was not able to distinguish betweenthese two opposing hypotheses, and "no threshold" provides more margin of safety. Since then, ourunderstanding of biological processes related to birth and growth of cancer has greatly expanded. Wenow understand that two different biological processes can enlarge cancer risk. Increasing the rate atwhich cells divide is one of these; increasing the rate at which mutations occur, independently of celldivision (mitotic) rate, is another.It is known that mitotic rate is under close physiologic control, operated through a complexsystem including a variety of intercellular messenger molecules. Functions controlled so as to be keptwithin certain limits in the face of external stressors must by definition exhibit a threshold in theirresponse to small changes in such external stress. It is only necessary to demonstrate the existence ofphysiologic control to show that the threshold must exist. Thus there will be a threshold in the responseto any nonmutagenic ("mitogenic") carcinogens.For classical mutagenesis as well, the weight of evidence favors the conclusion that thresholdsexist. Evidence for "no threshold" has almost no weight, either because of the limits on our ability tomeasure response at very low levels of mutagenic stimulus, or because it springs from anunacknowledged tautology. Conversely, there is evidence of moderate weight, primarily that cancerrates are not elevated in areas of high background radiation flux, that the mutation rate is under activephysiologic control.This expanded knowledge allows more reliable guidance for policy makers. First, policy shoulddistinguish between "mitogenic" and "mutagenic" carcinogens, those that act predominantly byincreasing the rate at which cells in certain tissues divide, and those that act directly on DNA.Mitogenic carcinogens should receive the same treatment as "noncarcinogens." At EPA, at least,policies are changing to reflect this understanding. Mutagenic carcinogens should be regulated usingthe "de minimus" approach FDA and EPA use for all cases other than direct food additives andpesticide residues. This approach relies on the concept of a "practical threshold," and provides veryadequate protection of public health.
关键词：regulation; cancer; science policy