The Linear No-Threshold Theory: A Crumbling Foundation
The idea that a known cause of cancer, e.g. ionizing radiation, poses a risk of cancer at any dose, no matter how small, is a central thesis informing modern environmental and occupational regulations and modern, which is to say low dose, toxic tort cancer litigation. In the toxic tort context plaintiffs regularly employ the logical fallacy of the appeal to ignorance (argumentum ad ignorantiam) to prove that even the slightest exposure was risky. They say that because defendants cannot establish a safe level of exposure it follows that every exposure is necessarily unsafe. The formal name for the idea that risk doesn't drop to zero until exposure drops to zero is the linear no-threshold dose theory or LNT. The LNT theory, always longer on theory and politics than evidence is increasingly under attack. Now even NIOSH has had to concede that at least in some circumstances there is indeed a safe dose for a carcinogen.
In "Checking the Foundation: Recent Radiobiology and the Linear No-Threshold Theory" the author states "a large and rapidly growing body of radiobiological evidence indicates that cell and tissue level responses to [radiation damage], particularly at low doses and/or dose-rates, are nonlinear and may exhibit thresholds ... this evidence directly contradicts the assumptions upon which the microdosimetric [LNT] argument is based". The idea that a substance that is harmful at high levels can be harmless or better yet beneficial or protective (the idea of hormesis) at low levels is discussed at length in this month's issue of Human & Experimental Toxicology.
The claim that "if it takes an ounce to kill ten men then a drop will thousands" was itself just a theory based on the idea that carcinogenesis was a stochastic process. Getting cancer was sort of like hitting the anti-lottery and the more tickets you bought (exposures you sustained) the more likely you were to lose yet if you were unlucky enough just one ticket could do it. Like black box epidemiology LNT was simply a way to ignore the formerly incomprehensible molecular biological mechanisms responsible for cancer. Now that those mechanisms are being uncovered and understood they can no longer be ignored as they shatter one paradigm after another.
