Answer to Question #11179 Submitted to "Ask the Experts"

Category: Radiation Effects

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


I'm a writer/producer working on a special about the effects of radiation on sea animals. I'm specifically interested in the marine animals on the top of the food chain, such as sharks, seals, whales, and dolphins. What would be the best way to test these animals for radioactivity and to gauge whether any radioactive waste has entered their bodies? This would be used to determine what effects the radiation may have on the animals. I'm looking for information about portable tools that could be used underwater or what scientific procedures should be used to best measure the radioactivity in the animals' tissues. I really appreciate your help and look forward to hearing from you.


This is an interesting question! Luckily we have a great deal of experience measuring radioactivity in just about everything, including marine animals.

The most reliable scientific procedure (standardized laboratory analysis) used to measure radioactivity in any medium is to obtain a sample and analyze it (counting the radiation emitted from the sample) using very sensitive radiation detectors. For example, we could catch a fish, grind it up, and then place a sample of the tissue into a sample counter. We can surround the sample and detector with lead to reduce background radiation, which increases the sensitivity of the counting procedure. Also, reducing the volume of (concentrating) the tissue by dehydration or ashing is another way to concentrate the radioactive material to improve the sensitivity of the analysis. Another way to increase counting sensitivity is to increase the amount of time the sample is counted. We want to have the highest sensitivity possible because normally the levels of radioactivity are so very low that they are difficult to measure.

As an animal swallows radioactive material in the seawater or in the food it eats (lower forms of life like plants and/or smaller animals) there is constant intake and elimination of the radioactive material. This constant intake and elimination causes the concentration in the animal's tissues to reach an equilibrium, just like we do with our daily intake of naturally occurring carbon-14 and potassium-40. To determine this equilibrium concentration in the tissue, it must be sampled for laboratory analysis. As the concentration of radioactive material in the seawater changes, the concentration in the animal's tissue also changes. The concentration of the radioactive material in the seawater would directly correlate to the concentration in the tissues of the animals that are feeding and living in the seawater. You won't have to harm a lot of animals to determine how much radioactive material is in each animal's tissue if you sample and analyze the seawater at the same time you catch the animal for sampling.

One recent study, in Deep Sea News, looked at the amount of radioactivity in tuna after the Fukushima accident (some marine scientists wrote about this online at "Detectable but Not Hazardous: Radioactive Marine Life of Fukushima"). The bottom line is that radioactivity is detectable in tuna but is not hazardous. In fact, the amount of artificial radioactivity is lower than the amount of natural radioactivity, which certainly poses no threat.

With respect to measuring radioactivity directly in seawater, there are waterproof radiation detectors that can be used. But these instruments are not sensitive enough to measure the dilute concentrations of radioactive material in the oceans. And incidentally, that's the opinion of marine scientists, who have no particular axe to grind with respect to radiation or nuclear energy, and a good summary is found on the Deep Sea News blog "True Facts About Ocean Radiation and the Fukushima Disaster."

The biological effects of radiation on marine animals will be essentially the same as they are with humans. Both would have the same long-term risks, which is a very slight increase in the risk of cancer. All humans have a risk of dying from cancer. About 19% to 23% of us will die from cancer, even if we are never exposed to radiation levels above natural background levels. According to the American Cancer Society's website there would be no giant or super sea creatures produced by the dilute amounts of natural and man-made radioactive material found in seawater. Also, there is essentially no increase in mutations in the generations that follow the exposure of the parent animals.

Because the radioactive material in the ocean is so dilute and the water itself absorbs radiation and is a very good shielding material, very little if any exposure will be from the water outside the animal. Essentially all exposure will be from radioactive materials ingested by the animal.

P. Andrew Karam, PhD, CHP
John P. Hageman, MS, CHP

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