What is the risk from radiation on imported food from Japan?

Question

I'm currently resident in Hong Kong a country which appars to import heavily from Japan.

Last saturday 7th May I went to a restaurant: http://www.openrice.com/english/restaurant/sr2.htm?shopid=39760

which I later discovered is themed after a popular Japanese coffee brand. I had one of those Fried Pork Chops in breadcrumbs which was served on a bed of white "pearl" rice with Japanese (style?) curry sauce

It occured to me that the rice may have been imported from Japan. I was interested in trying to identify the lifetime cancer risk from such a potential exposure. I have read that ingested isotopes are worse than external contaminations which can be washed away.

I'm aware that imports have been screened by the local goverment but from what I saw on the television it looked like they were just using dosimeters on the outside of cargo containers rather than in depth sampling.

I'm also wonder what types of isotopes would have been released in the fallout from Fukushima and in what ratios. I'm aware of Iodine 131, Caesium 134 and 147 and Strontium 90 but I've not seen any data on the ratios of what was released.

I've read that there are many Rice farms around Fukushima in Northern Japan and these provide approvimately 25% of the nations annual production.

Answer 1

Indeed, it's likely that the rice came from Japan, and if it did, it's pretty likely it came from the Fukushima region which is famous across Japan and beyond for its rice - and other products. However, it could have been harvested before the tsunami. But as discussed here,

Are these radioactive particle matter and air emmissions dangerous, 2000KM from Fukushima?

the measurements indicate that the contamination of all these products has been minimal even when it was found, and you would need to eat many kilograms of this rice - or something else - to approach the radioactive dose that you obtain from one healthy banana (produced outside Japan).

Of course, I can't guarantee that one particular package of rice couldn't contain an amount of radioactivity that is higher by three orders of magnitude - but it's just unlikely. Don't get me wrong: if I were you, I could react in the same sensitive way. But from my perspective right now, you will shorten your life much more visibly by the worries than by the actual radioactivity.

The radioactive content in that food is almost certainly pretty much indistinguishable from the natural levels. No one could have harvested rice and other plants in the truly contaminated areas around the power plant after the nuclear hassle (and only then it mattered) - because they had been evacuated. And the contamination in the more distant places is just small and when one computes what can get inside rice and survive for long enough time, it's negligible.

Moreover, when you eat radioactive isotopes, it's actually not the most permanent source of radioactivity and cancer risk. This stuff mostly gets out of your body within two months or so. Breathing plutonium is more risky. See this summary of the health impact of the basic radioactive isotopes:

http://motls.blogspot.com/2011/03/radioactivity-sieverts-and-other-units.html

Again, there is no reason to think that by eating the rice, you have been overexposed to these isotopes.

Answer 2

To address the component about in-depth searches of containers - Iodine 131, Caesium 134 and 147 and Strontium 90 decays involve high energy gamma rays, which readily penetrate cargo containers, so scanning the surface of the shipping container is sufficient to detect these isotopes with the appropriate equipment.

The science correspondent at National Public Radio in the US did a very nice piece in the aftermath of the disaster (link to NPR story about the impact of Fukushima fallout on food) where he interviewed a health physicist studying the fallout situation. The health physicist had demonstrated that you would need to drink 58,000 glasses of milk contaminated at the highest levels found by the date of the article to raise your lifetime cancer risk by 4%. As Luboš noted above, the farmlands have been evacuated. So the evacuation and halt in production combined with the scanning of imports at the port of arrival and the natural boost in isotopic reduction through decay means the likelihood of ingesting any amount of harmful isotope is small, and very likely nowhere near enough to cause serious health problems.