Ocean Radioactivity is the level of ionizing radiation found in a given sample of water. For the ocean this is measured in Bqs, or Becquerels. The radiation consists of Alpha particles, Beta particles and Gamma radiation. Globally, the level of ocean radioactivity is relatively low. However, in certain regions where nuclear disasters have taken place, the radiation levels can be very high. The radiation comes from the radioactive isotope of Caesium, Caesium 137.
Caesium 137 is called a ‘fission product,’ meaning that it is the result of the natural decaying of nuclear fuel rods from nuclear power plants. These power plants usually use Uranium 235 to generate their energy. Uranium can generate many different types of radioactive isotopes during its decay, however the primary isotopes that cause the most damage are Caesium 137 and Iodine 129. These products have different half-lives, meaning that some linger for only a few weeks while others hang around for decades. Cs 137, for instance, has a half life of 30.17 years ± .03 years. Cs 137 is readily absorbed by the body and many forms of life, making it a potent toxin. In the areas of Europe affected by the Chernobyl disaster, Cs 137 can still be detected in agriculture.
Caesium 137 isn’t distributed evenly, as certain regions of the globe produce more of it. For instance, the Chernobyl disaster emitted massive amounts of nuclear waste in the form of particulate matter into the atmosphere. These particles quickly decayed into Cs 137, and by the time the Western blowing wind set the particles down, they were over the Baltic sea. These particles raised the radioactivity of the sea to 40 Bq/m3, many times higher than other seas. In addition to this, the radioactivity lingers in certain regions, bioaccumulating in organisms and being passed down the food web.
A perfect example of this radioactive bioaccumulation is Tuna. Some types of tuna, such as Bluefin. Juvenile Bluefins fed in the radioactive waters of Japan during the 2011 Fukushima Daiichi disaster. They absorbed large quantities of radioactive particles and were irradiated heavily from the water itself. These fish then migrated across the Pacific Ocean to California. When the Tuna are caught, killed or die naturally, the bio accumulated radioactive particles will be passed on to the consumer, the predator or the ecosystem in which the Tuna dies. This is a perfect example of how ocean radioactivity can be transported across great distances.