Radioactivity is confusing at best.

The contaminant of concern according to CRIIRAD is Iodine 131. I131 has a half-life of 8.02 days. The article here http://www.euractiv.com/en/health/radiation-risks-fukushima-longer-negligible-news-503947 discusses level of a risky dose as:

"According to the directive, the impact of nuclear activity can be considered negligible if doses of radiation do not exceed ten micro sieverts (mSv) per year. Beyond this value, possible measures should be considered to reduce exposure, it says.

While radioactive iodine-131 is mostly present in the air in the form of gas, CRIIRAD notes that in the case of the Fukushima fallout, the main issue is to limit ingestion of iodine-131.

CRIIRAD notes that the amount of iodine-131 capable of delivering a dose of 10 mSv varies greatly depending on the age of consumers. Children up to two years old are the most vulnerable and ingestion of 50 becquerel (Bq) is enough to deliver to the body a dose of 10 mSv, according to the institute.

If the foods (leafy vegetables, milk etc.) contain between one and 10 Bq per kg or more, it is possible that the reference level of 10 mSv may be exceeded within two to three weeks, the institute added.

Radioactive iodine-131 values measured by the French Institute for Radiological Protection and Nuclear Safety (IRSN) in recent days show the following, varying levels of contamination: 0.08 Bq/kg in salad, spinach and leeks in Aix-en-Provence, 0.17 Bq per litre in milk in Lourdes and 2.1 Bq per litre in goats milk in Clansayes."

So in summation: 10mSv/year is bad

50 bq can deliver a body dose of 10 mSv in children

1-10 bq/kg food can deliver the reference value of 10 mSv (thats a huge range 1-10)

It is important to note that the relationship between bequerels and sieverts is extrememly hard to understand - here's some info (light reading): http://www.radiation-scott.org/radsource/2-0.htm

http://en.wikipedia.org/wiki/Sievert

http://en.wikipedia.org/wiki/Becquerel (side note I HATE citing wikipedia but it's the best non-textbook resource for a quick look - please do not quote wiki as it is not properly peer reviewed!)

You can honestly spend hours, days, years, a lifetime coming to understand radioactivity - and the truth as I believe it is that there are not that many people out there that truly understand how radioactive materials affect our world and affect us.

Be cautious and well informed. Pay attention to the news reports - but ALWAYS read the accompanying documentation and try to tease out the important tidbits of info.

Sorry that this isn't super clear - but thats kind of the point. The news media can barely get straight-forward information correct - so please read carefully and research often.

i live in japan, though quite far from fukushima, and, frankly, i do nothing: : : avoiding what can be realistically avoided (veg oils, chemicals, wheat, franken-sugars, processed food-like substances, etc.) already already takes a lot of effort to worry about something that i personally can do nothing about

I do nothing - because there's nothing to do, and nothing to be concerned of. Would suggest investigating actual science, rather then depending on the news for anything close to reality.

speaking of book long posts, Nora Gedgaudas has a very long post about the subject, particularly about supplementing with iodine pills (short version: be careful about doind this, it could easily lead to more problems) and recent radioactivity concerns here:

http://www.primalbody-primalmind.com/blog/?p=1042

very unfortunate that the spent rods at the Japanese plant were kept there in pools instead of in casks (like they are required to be in Germany). Incidentally, the US does not require spent fuel rods to be kept in specially designed casks either. After all, that would be more expensive for the poor power companies.

I am trying to only buy fresh produce grown in less radioactive contaminated areas such as south and Central America. My daughter and I are switching to tropical fruit. Also we are especially avoiding milk and wheat products and leafy green vegetables unless hydroponically grown.

I live in Tokyo, and have stocked up on frozen imported meat from Australia and frozen vegetables from China for now. Not much else I can do other than move...

Eat locally if possible?

It seems to me that although computing Sv from Bq is nontrivial, it would be nice to find a dosage calculator that does this for ingestion of specific material. For example, if I ingest 1000 Bq of 137Cs, I should know the Sv dosage. Unfortunately I can't seem to find such a calculator.

Hmm, I found this: https://apps.who.int/fsf/Codex/GuidelineLevelsforRadionuclidesinFoods.pdf

According to this, for 131I, 134Cs, 137Cs, the rough conversion factor from consumed becquerels to sieverts is 10^-8.

So eating 0.1 Kg snack of anchovies from the 1,280 Bq/Kg (total of 131I, 134Cs, 137Cs) sample found by Greenpeace offshore Nakoso port (about 50Km from ground zero) would give you a 1.28 μSv dose.

I'm guessing that this "conversion factor" is very rough, but maybe it gives some kind of indication of the order of magnitude.

So we are talking about a dental xray. I personally would not worry about a one time dosage of that magnitude, though I don't like anchovies.

Be sure to know the difference between μSv (microsieverts) and mSv (millisieverts). You can think of μSv as relevant on the order of hours or days; mSv as relevant to years; and Sv as really really bad.

On the other hand, finding fish at these levels outside of 50km completely invalidates the assertion that dilution renders the radiation negligible. It's only one order of magnitude below where I would not want to think about eating it.

Also, Greenpeace found seaweed at over 127,000 Bq/kg over 50km from the site. That's quite a bit more scary, because just 0.1 kg of this seaweed gives you a 0.12 mSv dose. That won't kill you, at least not right away, but IMO it's probably a good idea to steer clear of the mSv range at the dinner table.

Which is too bad because I really like sushi.

I won't buy Japanese green tea anymore, giving up coffee may have to wait, haha. Although radioactive green tea may still be healthier than the Chinese crap with all their recent food scandals, which is a shame 'cause tastewise I prefer Chinese tea...

I don't sweat the rest, the tamari soy sauce I get is made in Austria and when I eat sushi I only eat salmon which mainly comes from fish farms in Northern Europe anyways (yummy...)

I'm glad Japanese porn is still safe :D (just joking ;))

its a small world, keeps getting smaller evey day. if a banana has twice the government safety limit of radiation i eat half the banana. the solution is in the math.