By: Dr. Dana Sackett with contributions and edits by Dr. Daniel Madigan, an expert in the field of radioactivity in the environment.
Articles ranging from fear-inducing hysteria to ‘everything is totally cool’ have been hitting the media about radioactivity in the Pacific Ocean over the last several years following the disaster at Fukushima. This week we try to disentangle some of the information (and misinformation) on radioactivity in fish and present some recent research on radioactivity in the Pacific Ocean.
First though, let’s define some terms and discuss what radioactivity is and where it comes from. Radioactivity is when an unstable atom (known as a radionuclide) with excess energy decays and changes into a more stable atom. This decay process emits radiation and can take seconds to thousands of years depending on the radionuclide. Radionuclides can also occur naturally or as a product of human activity.
Naturally-occurring radionuclides, and their radioactive decay, occurred on Earth before humans did. As a result, natural radiation occurs all around us. One example of natural radiation that you are currently being exposed to is radioactive uranium which can decay into radium, which in turn is a radionuclide that can decay into lead; all of which can be found pretty much everywhere (rocks, soils, rivers, oceans, plants and animals). Even the air we breathe has radioactive carbon (14C) that decays into a more stable carbon (12C). Many of the natural radioactive elements found in fish include radioactive potassium, polonium, carbon, and radium. The point is: radiation is everywhere. This is not to say that all radiation is safe; it is not. But the level of exposure and the type of radiation is what can make radiation problematic for fish…and people.
Some benefits of radioactive elements are that they can be used to age or date, amongst other things, fish, ice formations, rocks, fossils, and even the earth itself. This aging is possible because radionuclides decay at a constant rate. In fact, nuclear weapons testing in the 1950s and 1960s was one of the largest sources of manufactured radionuclides to the atmosphere. This drastic increase in radionuclides were recorded in the ear bones of fish alive at that time, and can still be used to age fish that are alive today.
Two radionuclides that are by-products of nuclear power, that are not found in the environment naturally, that often make up the majority of the radionuclides released during a nuclear disaster, and that decay slowly are isotopes of an element called cesium. For these reasons, and because cesium can accumulate in fish muscle (which we like to eat), these radionuclides are frequently measured in fish tissue and water to examine the impacts of nuclear disasters such as Fukushima or Chernobyl. 137Cs is of particular concern because it takes so long to decay and can accumulate not just in fish but in other animals as well (for example, us).
A recent study on 134Cs and 137Cs from Fukushima in the Pacific found that Pacific bluefin tuna caught off the California coast accumulated radionuclides from waters surrounding Fukushima before migrating across the Pacific Ocean. The study also states that despite the 10-fold increase in radioactive cesium in bluefin tissue, the doses of radiation from these Fukushima radionuclides were low relative to the radiation from radioactive polonium and potassium that are naturally present in fish. In addition, because water concentrations of radioactive cesium are still only high in local waters surrounding Japan, the authors suggest that these radionuclides could be used as tracers of migration and can identify species that use the waters near Japan but are caught elsewhere.
Currently, radionuclides from Fukushima have made their way across the Pacific Ocean, reaching certain areas of the west coast of America via water and fish. However, the concentrations and types of radiation from Fukushima near the west coast of America and throughout the Pacific are negligible (if not absent) compared to the same radiation we are exposed to daily from natural sources. For instance, the additional dose of radiation from Fukushima radionuclides by an average consumer of bluefin tuna from the study above would be equivalent to eating approximately 9 bananas. Further, doses of radiation from Fukushima to marine life fall orders of magnitude below the lowest protection level set for ecosystems by the Environmental Risk from Ionizing Contaminant: Assessment and Management. Regardless, it will be important to continue to monitor radioactive cesium in water and fish, particularly those fish that reside, even temporarily, near Fukushima to ensure these levels remain low throughout the Pacific Ocean.
A great guide to put radiation into perspective can be found here http://xkcd.com/radiation/ and described here http://deepseanews.com/2013/11/true-facts-about-ocean-radiation-and-the-fukushima-disaster/
References and additional reading material:
Andrews AH, DeMartini EE, Brodziak J, Nichols RS, Humphreys RL. 2012. A long-lived life history for a tropical. Deepwater snapper (Pristipomoides filamentosus): bomb radiocarbon and lead-radium dating as extensions of daily increment analyses in otoliths. Can J Fish Aquat Sci 69:1850-1869.
Behrens E, Schwarzkopf FU, Lubbecke JF, Boning CW. 2012. Model simulations on the long-term dispersal of 137Cs released into the Pacific Ocean off Fukushima. Environmental Research Letters 7:034004.
Buesseler KO, Jayne SR, Fisher NS, Rypina II, Baumann H, Baumann Z, et al. 2012. Fukushima-derived radionuclides in the ocean and biota off Japan. PNAS 109:5984-5988.
Doi H, Takahara T, Tanaka K. 2012. Trophic position and metabolic rate predict the long-term decay process of radioactive cesium in fish: a meta-analysis. PLoS One 7:1-6.
Chen J. 2013. Evaluation of radioactivity concentrations from the Fukushima nuclear accident in fish products and associated risk to fish consumers. Radiation Protection Dosimetry 1-5.
Fisher NS, Beaugelin-Seiller K, Hinton TG, Baumann Z, Madigan DJ, Garnier-Laplace J. 2013. Evaluation of radiation doses and associated risk from the Fukushima nuclear accident to marine biota and human consumers of seafood. PNAS 110
Gorur FK, Keser R, Akcay N, Dizman S. 2012. Radioactivity and heavy metal concentrations of some commercial fish species consumed in the Black Sea region of Turkey. Chemosphere 87:356-361.
Garcia-Orellana J, Rodellas V, Casacuberta N, Lopez-Castillo E, Vilarrasa M, Moreno V, Garcia-Solsona E, Masque P. 2013. Submarine groundwater discharge: natural radioactivity accumulation in a wetland ecosystem. Marine Chemistry 156:61-72.
Hosseini A, Beresford NA, Brown JE, Jones DG, Phaneuf M, Thørring H., Yankovich T. 2010. Background dose-rates to reference animals and plants arising from exposure to naturally occurring radionuclides in aquatic environments. J Radiol Prot 30:235–264.
Madigan DJ, Baumann Z, Fisher NS. 2012. Pacific bluefin tuna transport Fukushima-derived radionuclides from Japan to California. PNAS 109:9483-9486.