STANFORD – The earthquake- and tsunami-related problems at Japan’s Fukushima Daiichi nuclear-power plant have inspired endless commentary and speculation. Unfortunately, much of the debate about the disaster and its implications has been uninformed and problematic.
Radiation levels have increased by as much as 400 times the normal level 12 miles from the Fukushima plant; increased radioactivity has been found in milk, fish, and a variety of vegetables farmed in the region; and drinking water in Tokyo, 140 miles (225 kilometers) from Fukushima, has been declared unsuitable for consumption by infants. Several countries have banned imports of milk and vegetables from the affected region.
What are we to make of all this?
Radiation at these levels poses a minimal threat to human health for anyone outside the immediate area of the nuclear-power station itself. Most of the radiation is Iodine-131, which is good news for several reasons. First, this isotope has a short half-life – only about eight days – so it decays to negligible levels in a short time (in 10 weeks, less than 0.1% is left.) Second, it indicates that the source of the radiation is the reactor itself, rather than spent fuel rods (which harbor much longer-lived and more dangerous radioisotopes). Third, a readily available and effective antidote exists for those at risk: non-radioactive iodine, available in tablets or liquid, which blocks the uptake of I-131 into the thyroid gland.
Moreover, limits for radioactivity in food commonly incorporate orders of magnitude of the margin of safety, and are predicated on long-term ingestion. And Japan’s limits for radiation exposure are even more conservative (i.e., lower) than those set by international agencies.
Another factor that might mitigate radiation damage is a phenomenon called hormesis – a biphasic dose-response relationship in which something such as a toxic heavy metal or ionizing radiation that is harmful at moderate to high doses may actually produce adaptive beneficial effects at low doses. In other words, we don’t see a completely linear relationship between the dose of the potential toxin and a deleterious effect; rather we see a distribution that looks something like a “check mark,” with concentration on the horizontal axis and some measure of damage on the vertical axis.
Hormesis is a byproduct of evolution. From the beginnings of life on earth, organisms have been exposed to potentially harsh conditions, with individual cells commonly exposed to toxic substances such as chemicals and radiation. In order to avoid early death and extinction, organisms developed complex mechanisms to cope with such environmental hazards, including altering the synthesis of nucleic acids and proteins to activate pathways that protect against or repair damage.
For example, the biologist Paul Z. Myers of the University of Minnesota has described an animal study in which fish embryos experience non-linear toxicity from alcohol, a toxin that causes severe deformities in zebrafish embryos at high doses and prolonged exposure. According to Myers (http://scienceblogs.com/pharyngula/2011/03/will_radiation_hormesis_protec.php),
“I’ve done concentration series, where we give sets of embryos exposures at increasing concentrations, and we get a nice linear curve out of it: more alcohol leads to increasing frequency and severity of midline and branchial arch defects. With one exception: at low concentrations of about 0.5% alcohol, the treated embryos actually have reduced mortality rates relative to the controls, and no developmental anomalies.”
In other words, there appears to be a kind of overcompensation that explains the enhanced protective mechanisms that are elicited by small amounts of a toxin. Protective mechanisms are activated to a greater degree than would be necessary merely to neutralize the threat, resulting in a net beneficial effect.
There are some epidemiological studies that have been touted as offering real-world illustrations of hormesis in humans, but they have palpable shortcomings. An excellent analysis of them by surgical oncologist David H. Gorski, M.D., Ph.D. (http://www.sciencebasedmedicine.org/?p=11636) was prompted by an American pundit’s outrageous exaggeration of the likely benefits from hormesis in Japan. She declared that, “the only good news is that anyone exposed to excess radiation from the nuclear power plants is now probably much less likely to get cancer.”
But that would be true only for incremental radiation exposures at extremely low levels. In light of what we know now – and even with the data that we are likely to have in the near future – we cannot be certain about the exposures. Some workers at Fukushima are likely to have received higher doses of radiation (not only of I-131, but also of other, longer-lived, more dangerous radioisotopes, such as Cesium-137) than would activate the hormetic response; in March, three workers suffered radiation burns from highly radioactive water that breached their protective clothing. And people (especially infants or children) exposed to high levels of I-131 before they could be protected by iodine prophylaxis might well have received cancer-inducing doses.
One thing is certain: at all but extremely low doses – perhaps only slightly higher than background levels – radiation causes cancer. Beyond that, radiation physics and hormesis are very arcane and complex phenomena, and understanding them requires more than superficial knowledge.
If you want to comprehend all the nuances, get a science degree from M.I.T. or the Eidgenössische Technische Hochschule in Zurich. Otherwise, stay tuned, learn from the experts, and don’t jump to conclusions.