It's the Dose that Makes the Poison: The Importance of Numbers

Sometimes people claim that nuclear radiation is uniquely scary because you can't see it, or smell it, or detect it with any of the human senses, implying that "ordinary hazards" are not so sneaky.  We're even told that a single gamma ray can kill us--a statement that affronts both science and common sense.  Like all such claims, we need to examine this one in light of real-world experience, not by the exchange of uncheckable rumors.

Let's look first at other, non-nuclear, hazards that surround us daily.  How about germs that fill the air when people around us sneeze, cough, or just breathe?  How good are we at detecting germs?  From birth to death, we are continuously immersed in germs, but healthy bodies protect us from harm.  We don't need to see them.  Similarly, we are continuously irradiated by cosmic rays and the natural radiation of the soil, water, air, and the flesh of our bodies.  Life first arose in a prehistoric earth many times more radioactive than today's. 

We minimize our chances of getting disease, not by trying to develop germ-free bodies (not compatible with life), but by trying to maintain a healthy immune system.  Similarly, the natural radiation levels we encounter just by living, are not a danger, and that presumably is why humans have developed no organs to detect radiation.  It is not a danger.    Of course, there are levels of germs, and levels of radiation, that are harmful, but we don't normally encounter them in the natural world.

(Aha!  But how about the unnatural world of nuclear reactors?)  I won't tackle the theological issue of whether we can properly exclude humankind and its products from the natural world.  Let's just look at the numbers.  The proto-scientist, Paracelsus, said in 1540 that nothing is poison but the DOSE makes it so.  That is the basis for vaccination.  That is why ancient king-poisoners knew they could safely swallow a small mouthful of poisoned food, which in larger amounts could kill.  It's a fundamental principle of biology that assaults that don't kill you make you stronger.  

So the relevant numbers here are that the average natural radiation level where people live is hundreds of times the radiation levels permitted for exposure to the public from nuclear reactors and other sources of human-made radiation.  Natural radiation levels on this radioactive earth vary hundreds-fold from one place to another.   And the measured fact is, the higher the background radiation, the LOWER the cancer rate.  So if we had no radiation whatsoever from nuclear power plants, we could hardly measure the difference in human exposure, because the nuclear contribution to our total radiation dose is trivial.

A further irony is that our dose from increased use of medical irradiation in life-saving procedures is now commensurate with high natural backgrounds, further invalidating concern over the negligible doses from nuclear facilities.

The facts just stated show how we should respond to occasional reports of leakage or other incidental exposure of radioactivity.  The phrase "exposed to radiation" tells us nothing about hazard.  It's the dose that makes the hazard (if any).  The anti-nuclear activist, Sheldon Novick, correctly noted that "nuclear waste" is no more hazardous than many other industrial wastes, so if we hear of a spill of radioactivity, we should judge its hazard as we would a spill of oil or any other biologically harmful chemical:  What's the toxic dose?

While we're talking numbers, let me divert for a moment to talk units.  The unit of radioactivity used to be the Curie, which was about one gram of radium.  A gram is one-twenty-eighth of an ounce, so that's a reasonable unit.  When the metric system came in, the unit of radioactivity became the Becquerel, named after another radiation research pioneer.  The Becquerel (Bq) is a single atomic disintegration per second.  There are 37,000,000,000 Bq in a curie.  So levels of radioactivity that are entirely harmless are now measured in millions or billions of Bq, instead of a few milliCuries.

What does all this mean in the real world?  One example is the case of tritium, which is an isotope of hydrogen that usually shows up as water. It is used widely to light exit signs without electricity.  It doesn't stay in the body long, and its radiation is low-energy.  So its biological impact if ingested is low, and the US permissible limit in drinking water is 20,000 picoCuries (millionths of a millionth of a Curie) per liter, which is estimated to give the body a 4 mrem dose.  This is about 1% of the average dose we receive from natural  radiation background. 

Recently, some tritium was detected in the soil near the Vermont Yankee nuclear plant, leading quickly to demands that the nuclear industry be shut down.  Previous minor leaks elsewhere led to industry promises to make all plants "zero leakage."  I've always avoided, as a matter of principle, promising there will be no more accidents. One cannot be sure to deliver on such promises.  What we should promise, is that we will ensure that accidents will not cause significant harm to people or the environment.  And that is the situation here.  If we look at the potential dose (i.e. toxicity) from such a leak, we find that it is considerably LESS than from numerous small leaks of oil and other chemicals that occur from time to time.  

In these more hazardous cases of non-radioactive spills, we devote a modest effort to cleaning up the area, leaving earth or concrete permanently stained and contaminated to the degree that, if you tried to eat it, you might suffer some deleterious effects.  And we rightly conclude, that's a reasonable course.  (Maybe we should post OSHA warning signs: DO NOT EAT THE DIRT.)  There is no realistic justification for requiring that the ground be decontaminated to hospital or "clean room" standards.  

Radioactivity is not unnatural, nor uniquely hazardous per se.  Many of the new chemicals we use in abundance, such as pesticides and other organics designed to interfere with natural functions, more nearly fit that characterization.  Radioactivity does not multiply, like germs; instead it decreases in toxicity.  We should stop viewing radiation as demonic and recognize its place in the natural world, and its special role in healing.  Even after large spills of oil (and there are many), we don't demand that the oil industry be shut down.  Let us base our judgments of danger on measured toxicity, not some panic-driven demand for a radiation-free planet.

Comments

[Paul Lindsey]

As a retired naval nuclear power officer, I ardently support a "full steam ahead" approach to new nuclear power plants (and keeping the ones we have going for their useful lives).

"And the measured fact is, the higher the background radiation, the LOWER the cancer rate." is a pretty broad statement. What is the source?

[John Tjostem]

I have researched the literature for evidence of benefits from low dose radiation.

A process known as radiation hormesis mediates its beneficial effect on health. Investigators have found that small doses of radiation have a stimulating and protective effect on cellular function. It stimulates immune defenses, prevents oxidative DNA damage, induces DNA repair enzymes and suppresses cancer. Government authorities and regulators – including the news media – ignore this data.

1) Life Span Study (LSS) of the Hiroshima-Nagasaki A Bomb Survivors
150,000 to 200,000 residents were killed by the blast and the heat of the explosion. 1990 data indicates only 344 excess solid cancer deaths and 87excess leukemia deaths in the study cohort of 86,572 survivors---less than one percent
Atom bomb survivors in Nagasaki who received 1,000 to 19,000 mrem of radiation have had a lower incidence of cancer, especially with regard to leukemia and colon cancer, than the non-irradiated control population. And it is turning out that Japan’s atom bomb survivors are living longer. They have a death rate after the age of 55 that is lower than matched Japanese people not exposed to radiation. (Don’t expect to hear this on the evening news.)

2) Another important epidemiological study has tracked the cancer mortality in people exposed to radiation from a thermonuclear explosion in 1957 in the former Soviet Union (in the Eastern Urals). Investigators followed 8,000 people who lived in the area for the next 30 years. The group exposed to 12,000 mrem (120 mSv) had a 39 % lower cancer mortality compared with a non-irradiated control group, exposed only to a normal 100 mrem of natural background radiation. The group that received a considerably higher dose of 50,000 mrem (500mSv) had a 28% lower, not quite as good, but still statistically significant decrease in cancer mortality.

3) Chernobyl accident
Fewer than 200 deaths recorded. No increase in mortality due to radiation has been observed, despite the prediction of 4000 excess cancer deaths (using the invalid LNT hypothesis– against the advice of the scientific societies). “This is an example of the deeply immoral use of our scientific heritage at a time when many scientists have a good understanding of the response of living organisms to low doses of radiation”.
J. M. Cuttler and M. Pollycove

4) People who live in Ramsar, Iran, a resort on the Caspian Sea, are exposed to natural background radiation of 79,000 mrem per year, 5,266 times more than what the EPA’s 15-mrem/year radiation safety standard allows. The local river and its streams have a high concentration of radium, which is 15 times more radioactive than plutonium. Its 2,000 residents do not have an increased incidence of cancer, as the linear hypothesis would predict, and their life span is the same as that of other Iranians. They have higher levels of DNA repair enzymes than the control population.

5) In Taiwan (in the early 1980s), 180 apartment buildings were built with recycled steel that was accidentally contaminated with Colbalt-60. The buildings’ occupants, 4,000 people, lived in them for more than 10 years before their radioactive state was discovered. The amount of radiation they received ranged up to more than 1,500 mrem per year. (Colbalt-60 has a half-life of 5.3 years.) The cancer mortality, over 20-year period, in the radiated occupants was 97 percent less (3.5 deaths per 100,000 person years) than that of the general population of Taiwan (116 deaths per 100,000 person years). Even the incidence of congenital heart malformations in the children they bore was reduced. This carefully done study shows, as its authors put it, that ”chronic radiation” [far above EPA limits] is an effective prophylaxis against cancer.”
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[Zack M]

It is sadly disturbing, yet all too human, that the truly benign waste-- nuclear waste-- has entire committees appointed with 'blue ribbon' panelists to try and decide 'what to do with it' which is only a concern since the IFR was cancelled by team Clinton. And yet, the truly dangerous waste, fossil fuel waste, is only now being criticized with a similar level of scorn since scientists like Lovelock or Hansen are warning that the Venus syndrome could make Earth uninhabitable for higher forms of life due to greenhouse in a couple of hundred years. Whether humans will go extinct or not I don't know, but maybe in the distant future some future civilization won't make the same mistakes we made. The patent disregard for science, the desire for nothing but 'growth' of 3% per year, meaning fossil consumption would be 16 times greater in 96 years, indicates to me that we are sleepwalking towards the edge of a cliff.

[Neil Craig]

There is simply no evidence whatsoever for the LNT theory. It was adopted in the 1950s simply because of the Precautionery Principle & to make paperwork easier & is now the cornerstone of all anti-nuclear claims.

This may be the time to scream & shout simply because "scientific consensus" no longer cuts any ice with the global warming "consensus" proving false. Time for science to clean its stables.