Should I be worried?
The ocean contains many small sources of naturally occurring radiation that in most places exceeds the dose provided by radioisotopes released from Fukushima. In addition, the remnants of nuclear weapons testing in the 1960s and 70s are also still detectable around the world. Except for locations on land in Japan and sites near the Fukushima Dai-ichi nuclear power plant, all of these sources combined pose little risk to human health. [ MORE ]
To describe the level of radiation in seawater samples, we use Bequerels (Bq), which equal the number of radioactive decay events per second, and report this number per cubic meter (1,000 liters or 264 gallons) of water. A typical sample will likely contain less than 10 Bequerels per cubic meter (Bq/m3) from cesium-137, thousands of times less than the radioactivity produced by naturally occurring isotopes such as potassium-40. By comparing the amount of cesium-137, which has a relatively long 30-year half life, and cesium-134, which has a much shorter, 2-year half life, we can “fingerprint” the contamination from Fukushima and estimate how much was released into the Pacific.
To understand exposure, we need to consider this number as well as the type of radiation produced (alpha particles, beta particles, or gamma rays) and the method of exposure (external or internal). Exposure is reported in Sieverts (Sv) or, more commonly, milli-Sieverts (mSv, or 0.001 Sv). Background radiation—the amount we receive from cosmic rays—amounts to 2 mSv at sea level. A single dental x-ray provides an exposure of as low as 0.005 mSv. [ LESS ]
How radioactive is our ocean?
impacts of radiation in the ocean
WHOI senior scientist Ken Buesseler discusses the presence and effect of radiation from Fukushima on the ocean and marine life.
Fukushima Plume predictions
Radioactive contaminants from Fukushima are carried across the Pacific Ocean by currents, the strongest of which is the Kuroshio, and spread along the West Coast of North America by complex coastal processes. Models predict that radionuclides from Fukushima will begin to arrive on the West Coast in early 2014, mainly in the north (Alaska and British Columbia) and then move further south in coming years before appearing in Hawaii in small amounts. The concentration of contaminants is expected to be well below limits set by the U.S. EPA for cesium-137 in drinking water (7,400 Bq/m3) or even the highest level recorded in the Baltic Sea after Chernobyl (1,000 Bq/m3).
RADIATION IN THE OCEAN
The background level of radiation in oceans and seas varies around the globe. Measured in atomic disintegrations per second (Becquerels) of cesium-137 in a cubic meter of water, this variation becomes readily apparent. The primary source of cesium-137 has been nuclear weapons testing in the Pacific Ocean, but some regions have experienced additional inputs. The Irish Sea in 2008 showed elevated levels compared to large ocean basins as a result of radioactive releases from the Sellafield reprocessing facility at Seacastle, U.K. Levels in the Baltic and Black Seas are elevated due to fallout from the 1986 explosion and fire at the Chernobyl nuclear reactor. By comparison, EPA drinking water standard for cesium-137 is 7,400 Bq/m3. (Data courtesy of MARiS/IAEA and CMER; Illustration by Jack Cook, courtesy Coastal Ocean Institute, Woods Hole Oceanographic Institution)
What About Marine life?
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Radioisotopes released into the atmosphere from the Dai-ichi nuclear power plant fell into the ocean.
Water used to cool reactors flushed radioisotopes into the sea.
Microscopic marine plants (phytoplankton) take up radioisotopes from seawater around them.
Contaminants move up the food chain from phytoplankton to tiny marine animals (zooplankton), fish larvae, fish, and larger predators. Different radioisotopes are taken up at different rates by different species.
Some contaminants end up in fecal pellets and other detrital particles that settle to the seafloor and accumulate in sediments.
Some radioisotopes in sediments may be remobilized into overlying waters and absorbed by bottom-dwelling organisms.
Scientists are tracking the many pathways by which radioisotopes from the damaged nuclear reactors at Fukushima make their way into and out of seawater, marine life, and seafloor sediments. These depend on the behavior and metabolism of individual animal, the nature of complex coastal and open-ocean processes, and the physical and chemical properties of individual isotopes.
Tale of the Tuna
Most marine life that becomes contaminated with Fukushima radiation remains near the reactor, but some species, like Bluefin tuna, are far-ranging and even migrate across the Pacific. When these animals leave the Northeast coast of Japan, some isotopes remain in their body, but others, like cesium, naturally flush out of their system. (Credit: Madigan, Baumann, and Fisher )