George Parris

The Myth of the Linear, No-Threshold Dose-Response Relationship for Carcinogens George Parris

ABSTRACT: The regulatory standards for low-level chemical and radiation exposure in virtually all developed nations are ultimately tied to cancer risk assessment. The risk assessment methodology that has been used most widely for the last 50 years is based on the hypothesis that the probability of cancer is a linear function of dose with no threshold, i.e., the linear, no-threshold (LNT) dose-response hypothesis. Application of this hypothesis to bioassay and/or epidemiological data frequently projects unacceptable risk from minimal exposures. Regulation of chemical and manufacturing industries to conform to these calculated exposures limits is frequently economically burdensome and leads to the abandonment of otherwise technologically attractive products, processes and applications. Moreover, incorporation of these standards into environmental remediation regulations as clean-up standards has frequently required very expensive alternatives for dealing with legacy contamination issues. Thus, many people have challenged the results of LNT analyses. In general, the regulatory agencies and courts have taken the position that the burden of proof is on the plaintiff in these situations and the plaintiff is put into the position of trying to "prove a negative." For practical purposes, this burden is impossible to carry. This manuscript takes a hard look at the origins of the LNT hypothesis and concludes that it is a myth. Literally, the LNT hypothesis was created by application of inappropriate assumptions to questionable data. Basically, the LNT theory never should have been accepted as "science" and should be required to meet a burden-of-proof standard itself in any scientific comparisons. In this manuscript, I will show that the methodology for cancer risk assessment used by regulatory agencies was arbitrarily parsed from the body of scientific literature available circa 1960, because it is simple to apply and inherently over conservative, not because it provided realistic scientific results. This manuscript has 322 citations of the literature.