Edward J. Calabresea,*, Robert J. Golden School of Public Health and Health Sciences, Department of Environmental Health Sciences, Morrill I N344, University of Massachusetts, Amherst, MA, 01003, USA b702 Linslade Street, Gaithersburg, MD, 20878, USA
ABSTRACT
The linear non-threshold (LNT) dose response model for cancer risk assessment has been a controversial concept since its initial proposal during the 1930s. It was long advocated by the radiation genetics community in the 1950s, some two decades prior to being generally adopted within the chemical toxicology community. This paper explores possible reasons for such major differences in the acceptance of LNT for cancer risk assessment by these two key groups of scientists.
1. Introduction
The US Congress passed, and President Richard Nixon signed into law the Safe Drinking Water Act in 1974. A significant provision of the Act involved engaging the US NAS to advise the EPA on multiple scientific and technical areas such as chemical and radiation risk assessment, including cancer risk assessment. To achieve these goals the NAS created the Safe Drinking Water Committee (SDWC) in 1975. In 1977 the SDWC published the 700 page Drinking Water and Health [1] report offering EPA widespread guidance, including cancer risk assessment and its underlying scientific foundations that supported the LNT. Within two years EPA would issue the first national drinking water standard for a chemical carcinogen using the LNT for total trihalomethanes (THM) [2]. This action would jump start an avalanche of other LNT based cancer risk assessments by EPA, not just for drinking water but for other environmental media as well. The decision to go linear by the SDWC for chemical carcinogens was therefore as highly significant as it was precedent setting, and led the way for future EPA cancer risk assessment actions. The actions of the SDWC to recommend LNT for chemical carcinogens was more than two decades after a similar recommendation of the 1956 NAS BEAR Genetics Panel to switch from a threshold to LNT for radiation induced mutation.This action of the BEAR Genetics Panel was soon followed by a recommendation of the National Committee for Radiation Protection and Measurement (NCRPM) to generalize the LNT concept to somatic cells for cancer risk assessment. This two decade time gap in the decision to go linear for cancer risk assessment for ionizing radiation and chemical carcinogens suggests the possibility that chemical toxicologists and radiation geneticists/cancer researchers may have evolved considerably differently with respect to the concept of cancer risk assessment, prompting the present paper.
LNT is the same sort of rationalization that leads to the idea that more CO2=dangerous climate change.
A rationalization that if ores the data.
LNT was of course a convenient basis on which to regulate, but it was never an effective model of how anything works in the real world.
Easiest of all examples to comprehend: viral and bacterial infection.
As we all know from our history teachings, the people living in the Americas had no exposure to several diseases that were common in the “old world”, including small pox. And that as part of the so-called “Colombian Exchange”, the native populations in the Americas were severely impacted by deaths due to exposure to the “old world” diseases, while the European and imported African slaves were not impacted as much. Being exposed to low concentrations of pathogens, especially “dead” pathogens, clearly helps build immunity to infectious diseases.
Of course, even that bit of history has been greatly exaggerated and overblown, because in many instances the native American populations were not decimated by disease exposure but also because they practiced no means of disease control, such as sanitation, or dealing with sick persons and the dead, and relied (unlike Europeans) on drinking water, while Europeans relied much more on fermented alcohol beverages for moisture intake, so were much less inclined to drink contaminated water. The Europeans may not have understood bacterial and viral infections, and how infectious diseases worked, but by the 16th century and beyond they had devised a variety of means, even if unwittingly, that led to lower mortality rates for “old world” diseases. Europeans also were ravaged by “New World” diseases for which they had no immunity.
As always, the simplest models for how stuff works are almost always the least accurate models for how stuff works.
This article and comment string put me in mind of Dr. Bruce Ames, made famous by the cancer screening test for chemicals known by his name and, he protested, made infamous by its misuse. He was quite a guy and I saved several of his papers. Here is one that is summary in nature, “Science and the Environment: Facts v. Phantoms”. https://fee.org/articles/science-and-the-environment/
Radiation limits were originally based on a wild best guess. Take the lowest known level of radiation for which acute effects can be detected and divide by 10. But what is not included in any limit or LNT value is individual susceptibility and specific cancer outcomes. Low dose radiation lowers the risk for most cancers but not all. Lukemia is one that may have an increased risk at a lower dose levels but is again highly dependent on the individual. So the real question with LNT is this: Does the lowering of risk for a dozen cancels, as an aribitrary example, outweigh the rising risk for one cancer. In short, it can be a legal nightmare.
Until reading this report I had thought that Brexit might be the most costly face-saving exercise in the history of man. But now I’m wondering whether LNT isn’t more deserving of that dubious distinction.
My fault, prior placed on the following thread when that’s the according thread:
Due to the low population density, there are hardly any medical centers in north siberian. In addition, the younger population mostly emigrates for education and training to the larger cities. So “medical trains” regularly visit and drive through the region.
https://www.google.com/search?client=ms-android-huawei&ei=E7InXbekD-2urgTUlIX4DQ&q=siberia%27s+medical+train&oq=Siberian+medicaltrain&gs_l=mobile-gws-wiz-serp.