From: Roger Greenway, ENN
Published August 18, 2013 07:41 AM

Is the linear dose-response model valid?

Scientists commonly use the linear dose-response model to estimate the potential health hazards of everything from radiation to asbestos, to toxic organic chemicals. There are some who question this model which usually takes data from extremely high-dose lab experiments with animals and extrapolatea the observed effects using a liner line to a zero dose. What is wrong with this approach is that at least for some hazardous substances, there is a dose below which there is not only no adverse effect, there is a positive effect! Think of the metals in your multi-vitamins, for example. So why is the linear no threshold model used? Good question. Some may argue that is is inherently conservative, so it should be used to be sure we are protecting people.

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In two recently published peer-reviewed articles, toxicologist Edward Calabrese of the University of Massachusetts Amherst describes how regulators came to adopt the linear no threshold (LNT) dose-response approach to ionizing radiation exposure in the 1950s, which was later generalized to chemical carcinogen risk assessment.

He also offers further evidence to support his earlier assertions that two geneticists deliberately suppressed evidence to prevent the U.S. National Academy of Sciences (NAS) from considering an alternative, threshold model, for which there was experimental support. Calabrese's articles appear in the July 26 and August 4 issues of Archives of Toxicology.

Calabrese says, "The regulatory research community needs to hear about this. This isn't an academic debate; it's practical, because all of our rules about chemical and low-level radiation are based on unvalidated assumptions and scientific panel decisions made without sound evidence. Now, after all these years, it's very hard when people have been frightened to death of any exposure whatsoever, to persuade them that we don't need to be scared by certain low-dose exposures."

The first of Calabrese's recent articles is a straightforward history of the LNT model for ionizing radiation mutation, a concept accepted by radiation geneticists in the 1950s and recommended by national and international advisory committees for risk assessment and human exposure guidelines and later generalized to chemical carcinogens ever since. It is now used by public health and regulatory agencies worldwide, he notes.

Photo of man checking for radiation leaks via Shutterstock.

Read more at UMass at Amherst.

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