Cigarette Smoke : Cancer Risk at Low Doses

Abstract

The regulation of exposure to low-dose carcinogens is beset with difficulties and uncertainties. Ethical considerations rule out the use of human experiments to determine risk from low dose carcinogens. Even if animal experiments are used, a number of animals would be required to test for carcinogens at low doses. Nevertheless, safe levels of human exposure must be set. Thus, methods based on extrapolation from animal experiments with a relatively small number of animals exposed to high dosages of potential carcinogens are being adopted as the basis for regulating human exposure to low dosages of carcinogens [1]. Since it has been impossible to determine a dosage level at which there is no cancer hazard, an alternate “virtually safe” dose method has become common. The virtually safe dose is a dose at which the cancer risk is no greater than some very small risk, say, a one-in 10⁵, 10⁶, or 10⁸ chance of developing cancer in a lifetime. For example, an action level of 100 μg/liter for total trihalomethanes in drinking water has been proposed by the EPA as prudent for these animal carcinogens [2]: the risk of cancer resulting from low-dose x-ray exposure has been determined in this way and used to establish acceptable x-ray dosage levels for mammography screening [3].