The linear no-threshold theory: Readers weigh in

Abstract

In their letter, Jeffry Siegel and coauthors discussed the linear no-threshold (LNT) model of radiation-induced cancer. Vital to any such discussion is the relationship of high-dose and low-dose radiation to cancer and radiological standards. The LNT model was primarily based on gamma radiation. The other types of radiation producers are alpha emitters and beta emitters. All three produce cancer, and that is important since cancer may soon surpass heart problems as the leading cause of death.Radiation exposure standards are based on studies of survivors of the Hiroshima and Nagasaki bombings. The resultant standards are thus inherently biased in favor of survivors.Data were collected five years after the bombing. Therefore, those studies—carried out by US investigators and not by Japanese medical personnel—and the standards based on them depend primarily on the memory of survivor interviewees rather than on actual exposure data. Much guesswork went into determining the dose that survivors actually received.After World War II, national and international organizations were established to study radiation health effects and recommend standards for acceptable radiation exposure for workers in the industry and for the general public. The principal organizations were the National Council on Radiation Protection and Measurements and the International Commission on Radiological Protection (ICRP). Exposure standards that emerged are based on analysis of radiation from external sources and do not include sources lodged in the body. The BEIR VII study,11. National Research Council, Committee to Assess Health Risks from Exposure to Low Levels of Ionizing Radiation, Health Risks from Exposure to Low Levels of Ionizing Radiation: BEIR VII Phase 2, National Academies Press (2006). which is the most comprehensive study of low-dose exposure to date and reinforces the LNT approach, concludes that any exposure to ionizing radiation is potentially harmful.Some alpha and beta emitters do lodge in the body and cause cancer and other illnesses. The European Committee on Radiation Risk started looking at populations exposed to internal radioactive isotopes from anthropogenic sources. Radioactive sources can enter the body through several means; ingestion, inhalation, and absorption through skin cuts are the main pathways. Most of the ingested or inhaled radioactive substances pass through the digestive system or are expectorated.Compared with gamma sources, alpha and beta emitters produce much smaller doses of electromagnetic radiation but do emit particles. Beta emitters—strontium-90 is an example—tend to migrate to bones and cause bone cancer.The manmade alpha emitter plutonium-239 can be found worldwide as a consequence of fallout from nuclear weapons testing and use.Many nuclear sites in the US have some 239Pu. At the Rocky Flats Plant just a few miles northwest of Denver, large quantities of 239Pu were used for construction of components for nuclear warheads. Residential housing sits on both the east and south sides of the facility, and there are nearby cities to the north. Residents living near the plant showed increased cancer rates, and many plant workers are receiving medical attention because of their exposure to 239Pu. The major pathway into the body for 239Pu is inhalation, because the particles are small. A Columbia University study found that a single plutonium alpha particle induces mutations in mammal cells.22. T. K. Hei et al., Proc. Natl. Acad. Sci. USA 94, 3765 (1997). https://doi.org/10.1073/pnas.94.8.3765 Once in the body, the 239Pu lodges in a specific location—primarily lung, bone, liver, brain, and gonads—and stays there. With a half-life of 24 110 years, it continuously emits alpha particles over the person’s lifetime.The Colorado Health Department stated that airborne emissions of 239Pu were the most dangerous emissions from the Rocky Flats facility. However, most airborne 239Pu particles are too small to be detected by the Environmental Protection Agency’s high-volume monitoring devices. But even if they could be detected, the EPA has no standards regulating airborne particles of 239Pu.Thus there are many questions remaining related to radiological standards and cancer.The discussion about radiation standards is based in part on work by LeRoy Moore, Rocky Mountain Peace and Justice Center, Boulder, Colorado.REFERENCESSection:ChooseTop of pageREFERENCES <<1. National Research Council, Committee to Assess Health Risks from Exposure to Low Levels of Ionizing Radiation, Health Risks from Exposure to Low Levels of Ionizing Radiation: BEIR VII Phase 2, National Academies Press (2006). Google Scholar2. T. K. Hei et al., Proc. Natl. Acad. Sci. USA 94, 3765 (1997). https://doi.org/10.1073/pnas.94.8.3765, Google ScholarCrossref, ISI© 2016 American Institute of Physics.