The linear no-threshold dose-effect relation: is it relevant to radiation protection regulation?

Official radiogenic cancer risk estimates for low-dose, protracted exposure conditions have been based on linear, no-threshold downward extrapolation from medium and high-dose effects among a population of A-bomb survivors, with the application of a downward correction for an assumed reduced biological effectiveness at low doses and low dose rates (DDREF correction). Neither in the follow-up of populations exposed to the high-dose A-bomb flash, nor from epidemiological data after low-dose occupational or medical irradiation is there any convincing evidence for this DDREF hypothesis--even less for a zero-effect threshold dose. To the contrary, for external low-dose exposures of nuclear workers or general populations, cancer risks per unit dose have been found to be about 1 order of magnitude larger than those derived from the Japanese survivors, with larger discrepancies for persons above 50 years of age, and for x-rayed fetuses. This may be due to a dose and dose-rate effect exactly opposite from that postulated by the DDREF assumption, and a dose-dependent bias due to selection for exceptionally high immune competence among the > 5 years A-bomb survivor cohort. Excess cancer mortality following occupational exposures to ingested fission products and radiation-associated teratogenic, genetic, and cancer detriment among diverse populations who had ingested small amounts of radioactivity after the precipitation of fallout at great distances from the Chernobyl nuclear explosion, suggest discrepancies of as much as 2 orders of magnitude with official risk estimates. Contrary to widely publicized statements, claiming that current regulations of population exposures are far too restrictive, thus unnecessarily costly for the radiation industries, the aggregate of radiation epidemiological evidence suggests that current standards are inadequate to protect public health.