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
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.
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  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) . 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.