FAQ: Contaminated Food In JapanFAQ: 日本の食品汚染について

We frequently get emails from people traveling to Japan asking if it’s safe to eat the food in country, for fear of contamination from Fukushima and thought the answer we’ve been sending out recently would be helpful/informative for others as well. [Edited to clarify that we think examining the risks in a scientific sense alone is insufficient.]

We want to be perfectly clear: we believe people everywhere have a right to uncontaminated food. True justice in this regard would mean a food supply that is clearly safe, one without Cesium or other contaminants, and a protection system that enjoyed the confidence and support of citizens. It would mean a robust third-party food monitoring system and adequate watchdogs were in place, and were allowed to crosscheck official findings freely and openly. Sadly, this is not yet the case in Japan, and is probably not the case anywhere else in the world yet either.

SAFECAST is not equipped yet to do our own food measurements, but we cooperate with independent food measurement labs and constantly monitor both official and independent results. There has been a lot of confusion about how food is being checked, how often, and by whom. This is mainly because the food monitoring system was not initially intended for informing the public as much as for providing guidance to producers and local government agriculture officials. So the results end up being hundreds of pages of confusing data.

Nevertheless, this monitoring system appears to have been effective in keeping food with contamination levels above the legally allowed level (100 bequerel/kilo or 100 Bq/kg) off the market. We say “effective,” not “perfect.” And although the 100Bq/kg level is the strictest in the world, some people insist it should be even stricter. A person’s decision about whether or not to eat local food should probably be based on whether or not they are comfortable with this 100Bq/kg limit.

Most of us would like to see the Japanese food monitoring system improved and made more clear to the public, and think people should clearly understand that the food contamination problem will be with us for decades, and that we should be prepared to be alert that entire time. Just because it looks ok now doesn’t mean it will be forever.

Japan is fortunate to have a food distribution system which provides people with items grown or caught all over the country and from overseas. While conceivably a family in Fukushima could eat only locally-produced food, in practice, like families throughout the country, only a portion of their diet is local, and this has effectively limited people’s exposure to contaminated items. Regular “extra portion” tests done independently by COOP Fukushima show what Fukushima families are actually eating. Since testing began in late 2011, out of 300 families tested most have actually had no detectable cesium in their meals, and in the case of those detected the levels have been very low, in the 10Bq or lower range. The levels of K40 (natural radioactive potassium) are much higher, and the Japanese diet has always included a fairly high dose of naturally-occuring Polonium 210, often found in shellfish and other seafood. The doses from these dwarf those seen so far from cesium.

The most carefully run independent and official food tests, internal contamination screening, and tests of actual meals all reinforce the conclusion that the actual amount of cesium and other radioactive contaminants finding its way into the food supply is much lower than was feared based on the contamination levels of farmland. Farmland decontamination, extensive food screening, and public awareness have all contributed to this. The fact that contaminated items still crop up occasionally and internal contamination screening results do not yet show 100% undetected for cesium shows that there’s still room for improvement.


Cesium has a biological half-life of about 70 days (shorter in children), and the body gets rid of it by excretion at a fairly constant pace. If a person consumes cesium once, for instance, half of it will be gone in 70 days, and it will eventually all be eliminated through natural processes, though it’s effects will continue as long as it remains in the body. With regular intake, it will build up in the body at a pace that reflects the ratio of the rate of intake to the rate of excretion, eventually reaching a plateau which will continue until the intake stops.

Let’s say you had fish that was contaminated with 100 Bq/kg of cesium. Although people rarely eat as much as 1kg of something like this in one day, let’s assume for argument’s sake that someone did. For a 10-yr old, eating 100 Bq/day, their internal cesium would plateau at about 5200 Bq after about a year; for an adult it would be about 14,000 Bq; and for a 1yr old, about 2000Bq. The 1 yr old’s effective dose from this would be about 0.08mSv/yr, the others proportionately (but not necessarily linearly) higher. These dose calculations account for the larger effect from internal contamination and for the different metabolism of children of various ages as opposed to adults.

Current Japanese guidelines are intended to keep doses from food below 1 mSv per year, a goal we think will protect most people adequately, though not perfectly. This 1 yr-old’s dose is less than 1/100 of that. Some may still argue that this is not low enough, and their concerns deserve to be given consideration, particularly since independent testing is not yet widespread enough to be sure.

If the Fukushima family whose meals tested highest for cesium (11.7 Bq/kg) ate that every day for a year, the adults would end up with a 0.14mSv effective dose, the kids less.

Here’s a more concrete example: A 70 year-old Minamisoma man was scanned for internal contamination 140 days after the accident, and had 20,000 Bq/body of Cs137 and Cs134 combined; he weighed 67 kg so his internal “body burden” of cesium was about 300Bq/kg, among the highest so far detected in Fukushima. The doctors checked his pantry, and found that he had been eating very contaminated mushrooms regularly (at over 142,000 Bq/kg), and also wild vegetables, etc, that had not been checked for contamination and had not been approved for sale. Several of the items he had gathered and was eating regularly, like wild ferns and chestnuts, were in the 500-1000 Bq/kg range. He was getting about 140 Bq/day intake of Cs137 and Cs134, and his effective dose for 1 year worked out to about 0.8mSv, just under the 1 mSv/yr level. The doctors advised him to stop eating those items, and he did, and his body burden decreased as expected according to the biological half-life.

For comparison, a 12-hour northern-route flight from Tokyo to the US exposes a person to about 0.04 mSv one-way, so flying that round trip would give them 0.08mSv. This is comparable to a year’s worth of 100Bq/day for a 1 year-old. There are lots of variables that make this kind of comparison difficult, and a lot of age-dependence, but even assuming internal exposures are several times more damaging than the standards indicate (and the jury is still out on just how the risks differ), a person needs to eat a lot of cesium-contaminated food to equal the radiation risk they get from regular air travel.

As we said above, however, the issue is not just about the science, but also about justice and the fact that the government has not yet really demonstrated a commitment to informing the public adequately about what’s in their food. Air travel is generally a matter of choice, but the contamination in the food supply was forced upon us. The contaminated food problem will need to be monitored for years. So by all means stay informed and stay vigilant, but at the same time we think it’s best to keep the risks in perspective.






日本で消費される食品の多くは海外から輸入されているという点で、ある意味幸運です。一方で福島の家族は地元で生産された食品だけを食べていると考えられています。実際に地産食品を消費している人達はほんの一握りです。これは汚染の影響下にある人を限定できる効果があります。 コープふくしまによって独自に行われた調査では、福島の家族が実際に何を食べているのかが調べられました。調査は2011年の終わりに始まり、300世帯の内ほとんどが実際に食事の中でセシウムが見つかりました。発見された数値は10ベクレルかそれ以下という低い値でした。K40(自然放射線であるカリウム)のレベルはもっと高くなります。日本人の食事には相当高い量の自然放射線であるポロニアム210がしばしば貝類や他の海産物から見つかっています。これらの小型生物からの放射線量は(福島原発事故で飛散された)セシウムよりもずっと高いレベルです。










About the Author

Sean Bonner


Sean Bonner is a co-founder and Global Director of Safecast. Based in Los Angeles, he's an Associate Researcher at the Center For Civic Media at the MIT Media Lab and a Shuttleworth Fellow.