On March 25th, 2011, Lewis Page wrote,

nobody has ever been able to show that this isotope [caesium-137] has any health consequences at all: huge amounts were emitted from Chernobyl, but no discernible illnesses have resulted.

However, Page is perhaps not a reliable source of information. A commenter on this blog wrote,

It seems Mr. Page is finally quieting down a bit. His comments seemed unduly rosy at the time he wrote them – with hindsight they defy polite comment. At the time of Mr. Page’s writing the meltdowns had already occurred but were not yet public knowledge. However what was known was bad enough and this was in no way reflected in Mr. Page’s writing.

I would especially like to point out Mr. Page’s belief that the Chernobyl catastrophy cost less than fifty lives.

And he provided these  three  links.

So what exactly are the health concerns with regard to radioactive caesium? Is it dangerous to breathe it in? To digest it? Wikipedia provides little  information about the effects on human health of exposure to radioactive caesium-137. Wikipedia also informs me that there are several radioactive isotopes of caesium. Caesium-137 has a half-life of about 30 years. (“The radioactive 135Cs has a very long half-life of about 2.3 million years.”)

The isotopes 134 and 137 (present in the biosphere in small amounts from radiation leaks) represent a radioactivity burden which varies depending on location. Radiocaesium does not accumulate in the body as effectively as many other fission products (such as radioiodine and radiostrontium). As with other alkali metals, radiocaesium washes out of the body relatively quickly in sweat and urine. However, radiocaesium follows potassium and tends to accumulate in plant tissues, including fruits and vegetables.[97][98][99] It is also well-documented that mushrooms from contaminated forests accumulate radiocaesium (caesium-137) in their fungal sporocarps.[100] Accumulation of caesium-137 in lakes has been a high concern after the Chernobyl disaster.[101][102] Experiments with dogs showed that a single dose of 3800 μCi (4.1 μg of caesium-137) per kilogram is lethal within three weeks;[103] smaller amounts may cause infertility and cancer.[104

This would suggest that the fact that people have radioactive urine is not a signal for mass panic: rather, their bodies are functioning normally and flushing the (presumably) caesium out.

So perhaps we should be more concerned about strontium. However, the media is all about caesium…

BTW, I recommend reading the Wikipedia entries on the Chernobyl disaster and on deaths due to the Chernobyl disaster. They provide perspective on what is unfolding in Fukushima. By that I mean firstly, there were many people who died immediately or within 3 months, due to acute radiation sickness. So far no-one has died from ARS in Fukushima or anywhere else in Japan since March 11. And secondly, it gives a hint as to how long the Fukushima disaster will continue (the Chernobyl disaster occurred on 26 April 1986, 25 years ago) :

Of the 440,350 wild boar killed in the 2010 hunting season in Germany, over 1,000 were found to be contaminated with levels of radiation above the permitted limit of 600 bequerels, due to residual radioactivity from Chernobyl.[100] Germany has “banned wild game meat because of contamination linked to radioactive mushrooms”.[101]

The Norwegian Agricultural Authority reported that in 2009 a total of 18,000 livestock in Norway needed to be given uncontaminated feed for a period of time before slaughter in order to ensure that their meat was safe for human consumption. This was due to residual radioactivity from Chernobyl in the plants they graze on in the wild during the summer. The after-effects of Chernobyl were expected to be seen for a further 100 years, although the severity of the effects would decline over that period.[102] In Britain and Norway, as of 2011, “slaughter restrictions remain for sheep raised on pasture contaminated by radiation fallout”.[103]

Without precise information about the type of isotope detected, articles like this one, while high in attention-grabbing and unease-causing power, do little to inform. (This one is even worse.)