Suggested Approaches on Communicating to the Public Implications of the Linear No-Threshold (LNT) Dose Response Model and the Fallacy That “There Are No Safe Levels of Radiation Exposure”

The linear no-threshold dose response model (LNT) is used to estimate health effects due to exposure to ionizing radiation. It has been used extensively by US regulatory agencies for many decades to establish radiation exposure limits and to estimate future health (primarily cancer) effects for both projected (e.g., for a proposed nuclear facility or activity) and previous radiation exposures. The model assumes a linear relationship between dose and health effects, even for very low doses within the range of natural background radiation, where biological effects may be difficult or impossible to observe or may not exist. The LNT model implies that all exposure to ionizing radiation is harmful, regardless of how low the dose, since it assumes there is “no safe threshold” for exposure to radiation. That is, based on the implications of the LNT model, any exposure could result in increased cancer and possibly undesirable genetic effects. A major objective of this paper is to provide data and approaches that we as health physicists can use to communicate these highly controversial and misunderstood concepts more effectively to the public. Our target audience is often not health physicists or physical scientists but a reasonably educated audience where the data, concepts, and approaches suggested herein can be useful. As health physicists, it is our nature to try and be as “rigorous” and “precise” as we can with our terminology and mathematical expressions. Trying to be effective communicators of scientific concepts to nonscientists in this manner can often be self-defeating rather than just communicating in a simple and “familiar” manner. For example, although it is suggested that both the international and US units of effective radiation dose millisieverts (mSv) and millirem (mrem) respectively are explained, it unnecessary to include in discussions with “the public” equivalences with other larger or smaller units such as Sieverts vs. Rem or microsieverts vs. microrem, which confuse and do not add to understanding of the basic concepts we are attempting to communicate. A similar approach should be used with units of radioactivity present, e.g., picocuries (pCi) vs. the international and/or larger equiveillances such as Becquerels (Bq) or Curies (Ci). The pCi is the only unit the US EPA uses for remedial action soil concentrations in their applications of the LNT described here and is the unit used by US commercial laboratories to report results, so it is already “familiar” to many people. Additionally, nonscientists/engineers are not necessarily familiar with scientific notation using powers of ten (10 x , e.g.) and in particular, negative exponents such as 3 × 10 -4 , but most people can understand that the decimal equivalent, 0.0003, is a very small number. Accordingly, some flexibility in communication is suggested relative to the health physics profession’s usual rigorous (and appropriate) application of our professional standards of practice. This paper attempts to present data and rationales for public communication that demonstrate (1) that numerous national and international professional and scientific bodies refute the appropriateness of the LNT “no threshold” model to estimate health effects from very low levels of radiation dose, including within the range of and/or below natural background; (2) “exposure thresholds” exist below which experts believe there is no evidence of measurable health effects; and (3) continued use of the LNT model for purposes of defining safety or “acceptable risk” at very low radiation doses and estimating cancer risks based on the LNT model is contrary to logic and common sense and is potentially detrimental to US society’s long term interests.