Answer to Question #9713 Submitted to "Ask the Experts"

Category: Nuclear Power, Devices, and Accidents — Nuclear and Radiation Accidents

The following question was answered by an expert in the appropriate field:


I understand that algae and seaweed are bio-accumulators of radionuclides. I was looking at the measurements from different places, and I noticed that algae-producing companies in Taiwan and Okinawa, Japan, have published certificates from the governments of their respective countries guaranteeing that their algae is free of any radioactivity. On the other hand, seaweed in Vancouver has tested positive for around 400 Bq of radioactive iodine per pound last week. Is that possible considering how much farther away Vancouver is to Fukushima compared to Taiwan and Okinawa? Do the wind patterns make that much of a difference?


You are correct that many organisms accumulate radionuclides. Although I haven’t seen any radiation readings specifically from Canadian seaweed, I have seen many radiation readings from a pretty large number of media (air, rainwater, drinking water, milk, etc.) from all over the United States—including the West Coast—and I think it’s safe to say that it’s not likely that there would be enough radioactivity in seaweed in Vancouver to cause a health risk.

The number you mention—400 Bq per pound—is hard to evaluate without more information. 400 Bq of iodine isn’t a whole lot of radioactivity and, by itself, is not likely to be harmful. Something to remember is that you have to eat a whole pound of seaweed to get this amount of radioactivity—I know that I’m normally eating seaweed a few grams at a time—a pound is about 400 grams or so which is a LOT of sushi! So my guess is that between the levels of radioactivity noted in the seaweed and the relatively small amounts of seaweed that most of us eat there is no health risk from eating this.

I guess I can say, too, that I was in Japan for 10 days (including a few days in the area immediately affected by the tsunami and reactor problems)—I just returned in early summer—and I didn’t worry at all about the food I ate anywhere. I was also making radiation measurements the whole time and never saw anything to give me pause.

So I think there are a few lines of evidence that there’s not really much (if anything) to worry about.

P. Andrew Karam, PhD, CHP

Answer posted on 14 November 2011. The information posted on this web page is intended as general reference information only. Specific facts and circumstances may affect the applicability of concepts, materials, and information described herein. The information provided is not a substitute for professional advice and should not be relied upon in the absence of such professional advice. To the best of our knowledge, answers are correct at the time they are posted. Be advised that over time, requirements could change, new data could be made available, and Internet links could change, affecting the correctness of the answers. Answers are the professional opinions of the expert responding to each question; they do not necessarily represent the position of the Health Physics Society.