In March 2011 Japan suffered a horrible “triple disaster” with a major earthquake, a resultant tsunami and a meltdown of three nuclear reactors. The nuclear reactor meltdowns caused releases of radioactivity to the air and to water used to try to cool down the reactor. Some of the radioactive water subsequently was released into the ocean or seeped through the soil into groundwater. Releases of radioactive water to the ocean were evidently still continuing as of July 2013 and may be increasing. Here's an assessment of the situation from August 2013 and another from November 2014.
Understandably, there has been international concern about the possible human health and ecological effects from exposure to the radiation. This concern is focused on the residents of Japan, primarily the workers at the nuclear power plants, the cleanup crews that continue to work at the power plant sites, and those who lived within the “fallout area” (about a 20 km radius) around the facilities. These people were exposed to airborne radiation, and were potentially also exposed to radiation from contact with soil or objects that had become radioactive. Continuing radiation exposure pathways include consumption of radioactive water (contaminated surface water or groundwater) and consumption of food (crops, meat, dairy products and seafood) that had been dosed by radioactivity. Exposure to radiation from contaminated water or food is a concern for anyone who might consume such products originating from the disaster area.
Although there have reportedly been no radiation-related deaths or acute effects observed among the workers involved at the accident site, there is concern about longer-term effects, including leukemia, thyroid cancer and other types of cancer.
Update: In October 2015 an article in the New York Times reported:
A man who developed leukemia after working on a cleanup crew at the ruined Fukushima Daiichi nuclear power plant has been awarded workers’ compensation by the Japanese government, in what amounts to the first official acknowledgment that exposure to radiation at the disaster site may have caused cancer.
An article published in the NY Times on March 1, 2013 referenced a World Health Organization (W.H.O.) study which estimated health risks for those in the most contaminated areas. The article stated:
“According to the W.H.O. study, girls exposed as infants to radioactivity in the most contaminated regions of Fukushima Prefecture, where estimated doses ranged from 12 to 25 millisieverts for the first year, faced a 70 percent higher risk of developing thyroid cancer than what would normally be expected. The report pointed out, however, that the normal expected risk of thyroid cancer was just 0.75 percent, and that the additional lifetime risk would raise that to 1.25 percent.
Girls exposed to radioactivity as infants in the most heavily contaminated areas also had a 6 percent higher risk of developing breast cancer, and a 4 percent higher risk of developing cancers that cause tumors. Meanwhile, boys exposed as infants had a 7 percent higher chance of developing leukemia.
The study also said that about a third of the emergency workers who remained to try to stabilize the Fukushima Daiichi plant were estimated to have a slightly increased risk of developing leukemia, thyroid cancer and other types of cancer.
There would most likely be no observable increase in cancer rates for the general population in Fukushima Prefecture outside the most contaminated zones, in the rest of Japan and the world, the report said. It also said that the radiological fallout from the disaster was not expected to cause increases in miscarriages, stillbirths and other physical or mental disabilities."
An earlier (July 2012), separate study by researchers at Stanford University predicted the total cancer casualties that would eventually accrue from the Fukushima nuclear disaster as 130 deaths and 180 additional cancers. The study, published in the journal Energy and Environmental Science, actually presents the health risks as wide ranges: between 15 and 1,100 fatalities and between 24 and 1,800 additional cancers.
In late May 2013, the NY Times reported on the results of a further evaluation of predicted health effects in Japan by the United Nations Scientific Committee on the Effect of Atomic Radiation (UNSCEAR). UNSCEAR stated:
“The additional exposures received by most Japanese people in the first year and subsequent years due to the radioactive releases from the accident are less than the doses received from natural background radiation (which is about 2.1 mSv per year). This is particularly the case for Japanese people living away from Fukushima, where annual doses of around 0.2 mSv from the accident are estimated, arising primarily through ingestion of radionuclides in food.
No radiation-related deaths or acute effects have been observed among nearly 25,000 workers (including TEPCO employees and contractors) involved at the accident site.
Given the small number of highly exposed workers, it is unlikely that excess cases of thyroid cancer due to radiation exposure would be detectable. Special health examinations will be given to workers with exposures above 100 mSv including annual monitoring of the thyroid, stomach, large intestine and lung for cancer as a means to monitor for potential late radiation-related health effects at the individual level.
The assessment also concluded that although the rate of exposures may have exceeded the levels for the onset of effects on plants and animals several times in the first few months following the accident, any effects are expected to be transient in nature, given their short duration. In general, the exposures on both marine and terrestrial non-human biota were too low for observable acute effects.”
It should be noted that this assessment does not say that there will be no deaths or cases of cancer from Fukushima radiation exposure, only that “it is unlikely that excess cases of thyroid cancer due to radiation exposure would be detectable” given the small numbers of highly exposed workers. Epidemiology (health effects) studies typically require large numbers of “subjects” in order to produce statistically valid results. It is clear that a significant number of people in Japan have been exposed to radiation and some may continue to be exposed through ingestion of water and food containing radioactivity.
There are four potential ways radiation from Fukushima can get to the United States (and beyond) – through air, water, marine debris and sea life.
Some of the air emissions were caught by the jet stream and carried eastward across the Pacific Ocean to the United States. Monitoring stations along the West Coast, including one at UC Berkeley School of Engineering did detect a spike in concentrations of radioactive iodine (I131, I132), cesium (Cs137, Cs134), and tellurium (Te132) beginning about March 16, 2011. These substances were also detected in rainwater and surface water samples collected from mid-March until about mid-April 2011. By April 4, 2011 U.C Berkeley noted: “There is clearly an ongoing decay in all species, with even iodine-131 dipping very close to our minimum detectable levels.” On April 10 they noted: “Air measurements have been updated to be current to 4/8. All species are now at our estimated detection limit.” On April 17 they noted: “We have updated our rainwater measurements with results from the rain collected on 4/13. Sharp decreases in activity are seen for all species that are still detectable.” On May 2 they noted: “There are no isotopes from Japan detected in the new spinach, kale, arugula, and seaweed samples. The new strawberry samples from 4/20 show no I-131, but Cs-134 and Cs-137 are present. The highest levels of radioisotopes detected would require the consumption of more than 3 tons of strawberries in order to receive the same equivalent dose as a cross-country airplane flight.” Regarding the health risk associated with the detected concentrations in the air, water and some food products, UC Berkeley wrote: “the risk from radiation at the levels we are measuring is still insignificant.” So, although there were detectable levels of radioactivity in air, water and crop samples collected along the West Coast beginning a few days after the release in Japan, the concentrations were not considered to represent a significant health threat and had generally declined to at or near the detection levels by about one month later.
In 2013, U.C. Berkeley Professor of Nuclear Engineering Eric Norman and his students tested radiation levels in fish, plants, milk, seawater, and salt from a variety of locations throughout the Pacific Ocean and coastal regions. With the help of Al Smith, physicist at Berkeley Lab and one of the world's experts on background gamma ray counting, and Keenan Thomas from UC Berkeley, the team analyzed and interpreted the results. They expected to find at least some cesium isotopes in the seaweed since it concentrates potassium, an element that's in the same column of cesium on the periodic table. The scientists sampled their fish, seaweed, and other Pacific products from Hawaii, the Philippines, the West Coast areas, and Japan. But none of these samples showed any indication of radiation from Fukushima. Read more about this.
Here's a graphic showing where radioactive iodine and cesium were detected across the United States in March 2011.
Some of the air emissions of radioactivity evidently settled on and were concentrated in kelp in California’s coastal waters. Similar to the air, water and food samples, the initial concentrations noted in kelp were undetectable in samples collected a month later.
Both the US EPA and private individuals continuously monitor radiation in air across the United States.
Large amounts of cooling water containing radioactivity were (and evidently still are) discharged into the Pacific Ocean near Fukushima. In additional, some of the airborne radioactivity could be expected to settle into the ocean or be scrubbed out of the air by rain. The prevailing currents then would transport this radioactive water eastward towards the United States. Along the way, concentrations should decrease substantially (several orders of magnitude) due to radioactive decay, dilution, dispersion, and the settling of some particles to the ocean floor. This transport has been modeled and depicted in computer animations to estimate the long-term dispersion by ocean currents of a slowly decaying “tracer” (half-life of 30 years, comparable to that of 137Cs) from the local waters off the Fukushima Nuclear Power Plants. The tracer was continuously injected (in the computer model) into the coastal waters over some weeks; its subsequent spreading and dilution in the Pacific Ocean was then simulated for 10 years. A summary of the computer model runs concludes:
“…the main tracer patch propagates eastward across the Pacific Ocean, reaching the coastal waters of North America after about 5–6 years. Tentatively assuming a value of 10 PBq for the net 137Cs input during the first weeks after the Fukushima incident, the simulation suggests a rapid dilution of peak radioactivity values to about 10 Bq m−3 during the first two years, followed by a gradual decline to 1–2 Bq m−3 over the next 4–7 years. The total peak radioactivity levels would then still be about twice the pre-Fukushima values.”
It should be noted that a baseline concentration of Cesium exists in the ocean due to atmospheric nuclear weapons testing conducted by the United States, France, and Great Britain during the 1950s and ’60s. Cesium concentrations in the western North Pacific Ocean pre-Fukushima had declined by 2010 to about 1/10 of the concentrations that existed in the early 1960s.
Another study was published in the October 2013 issue of the journal Deep Sea Research Part 1. The study authors conclude the plume will be harmless by the time it reaches US shores. Dr. Erik van Sebille of the Climate Change Research Centre at the University of New South Wales has stated:
“Observers on the west coast of the United States will be able to see a measurable increase in radioactive material three years after the event. However, people on those coastlines should not be concerned as the concentration of radioactive material quickly drops below World Health Organization (WHO) safety levels as soon as it leaves Japanese waters."
These predictions have now been supported by measurements indicating that Fukushima derived Cesium (Cs) had reached near the west coast (offshore from British Columbia, Canada) as of June 2013 and were detected at Ucluelet on Vancouver Island in February 2015 but that concentrations of Cs continue to be well below levels thought to pose environmental or public health threats. So far, the measured concentrations of Cs are lower than predicted by the models. See this presentation (October, 2013) and this article (February 2014) for more details.
An article Fukushima and Ocean Radioactivity by Ken O. Buessler was published in Oceanography, Volume 27, Number 1, a quarterly journal of The Oceanography Society. This article compares the amount of radioactivity released into the Pacific Ocean from Fukushima with the amount of radioactivity from natural sources and the amount of radioactivity released from previous and continuing man-made sources (nuclear weapons testing, Chernobyl, nuclear fuel reprocessing facilities).
Additional views on radiation risks from water can be found by listening to an interview with Dr. Ken Buesseler, a senior scientist at the Woods Hole Oceanographic Institution in Massachusetts and an earlier interview with Dr. Buesseler. And here's an interview with Dr. Buesseler in Surfing Magazine. Note that the map is a tsunami wave height map, not a radiation plume map.
Dr. Buesseler announced in January 2014 the launch of a crowdsourced radiation monitoring website that will allow people and communities to propose sampling sites along the Pacific coast. He does not expect to find unsafe levels of radiation, but he thinks the levels should be measured to allay people’s fears and to contribute to science, allowing regulators and oceanographers to get a better handle on how ocean currents travel. He is specifically interested in parts of the northern United States and Alaska, because the radioactive isotopes are projected to arrive there first. People who propose sampling sites will need to raise $100 in seed funding to move forward. Then, a fund-raising page will be set up to underwrite the full cost of testing—between $550 and $600—about one-third of which is necessary just to ship five gallons of water to the east coast. Once funds are raised to cover the testing, individuals will collect the samples and ship them to the Woods Hole laboratory, which can analyze between two and five samples per week. Here are the most current results.
In October 2014 the Woods Hole Oceanographic Institution reported that radiation from the Fukushima nuclear disaster was approaching the West Coast. A sample taken Aug. 2 about 1,200 kilometers west of Vancouver, B.C. tested positive for Cesium 134, the “fingerprint” of Fukushima. It also showed higher-than-background levels of Cesium 137, another Fukushima isotope that already is present in the world’s oceans from nuclear testing in the 1950s and 1960s. The sample is the first of about 40 offshore test results that will be made public at a conference on November 13, 2014. Read another article on recent testing. This article which appeared in the Statesman Journal on November 10, 2014 stated that very low levels of Cesium 134 had been detected in a sample collected about 100 miles off the coast of Eureka, CA. From the article:
"...this summer Buesseler partnered with a group of volunteers on the research vessel 'Point Sur' to take a series of about 50 samples offshore, from Dutch Harbor, Alaska to Eureka. So far, about 20 of those samples have been analyzed, and 10 have been positive for cesium-134, the Fukushima fingerprint. All were relatively close to the surface. The amount of cesium-134 in each sample was less than 2 becquerels per cubic meter (Bq/m3). That's about 1,000 times lower than the acceptable limit in drinking water set by the U.S. Environmental Protection Agency."
Dr. Buesseler was interviewed by Owen James Burke of The Scuttlefish in November 2014 to discuss the latest ocean measurements and put them in perspective.
In December 2014 a paper Arrival of the Fukushima radioactivity plume in North American continental waters was published in the Proceedings of the National Academy of Sciences. The paper, by John N. Smith of Fisheries and Oceans Canada (a government agency) and several colleagues, is the "first systematic study...of the transport of the Fukushima marine radioactivity signal to the eastern North Pacific," and concludes that radiation reached the continental shelf of Canada by June 2013, and has increased somewhat since. However, the levels of radiation are very low, well below levels that public health authorities cite as grounds for concern. The radiation "does not represent a threat to human health or the environment," reports the paper.
In December 2015 scientists monitoring the spread of radiation in the ocean from the Fukushima nuclear accident reported finding an increased number of sites off the US West Coast showing signs of contamination from Fukushima. This included the highest detected level to date from a sample collected about 1,600 miles west of San Francisco. The level of radioactive cesium isotopes in the sample, 11 Becquerels per cubic meter of seawater, is 50 percent higher than other samples collected along the West Coast so far, but is still more than 500 times lower than US government safety limits for drinking water, and well below limits of concern for direct exposure while swimming, boating, or other recreational activities.
It was mentioned above that some airborne radioactivity (Iodine-131) was deposited on kelp shortly after the Fukushima disaster in 2011, but that concentrations were undetectable a month later. It's also possible that kelp will pick up low levels of radioactivity (Cesium-134 and Cesium-137) from seawater as the plume of radioactivity reaches the West Coast. To evaluate this, researchers from several universities and research organization will participate in a Kelp Watch 2014 project to sample Giant Kelp and Bull Kelp throughout the year from 35 different locations by individuals from 20 academic and government institutions and 2 educational student-oriented private organizations. More on this. Results from the initial round of testing were announced in May 2014. No Fukushima-based radiation was detected in the collected kelp samples.
Some marine debris from the disaster in Japan has already made its way across the Pacific Ocean and has come ashore in Alaska, British Columbia, Washington, Oregon and California. We can expect additional debris to continue to make its way to our shores for many years. To date, none of the Tsunami marine debris has tested positive for radioactivity. The primary reason for this is that the tsunami washed debris out to sea before the release of radioactivity from Fukushima. In addition, any radioactivity present on the debris would be subject to decay and flushing by seawater and rainwater during its journey across the Pacific. It is not expected that marine debris will represent a future health threat.
Fish and other marine life living in the coastal waters of Japan have been detected as having significant levels of radioactivity. In fact, some fishing areas around Japan remain closed due to high levels of radioactivity in bottom sediments and fish. Consumers of seafood in Japan have legitimate concerns about the long-term heath effects of consuming fish contaminated with radioactivity. An article on the website of Woods Hole Oceanographic Institution explains:
“There is, however, more concern about the Fukushima radioisotopes that end up in fish and seaweed—mainstays of the Japanese diet. “Here we’re talking about accumulation in something you’re going to eat internally versus being exposed to externally,” Buesseler said at the Fukushima and the Ocean conference in Tokyo in November 2012. Monitoring of cesium in fish taken from affected areas continues to show an unexplained persistence of higher-than-pre-disaster levels, and the occasional anomalies of individual fish caught near the power plant that register sky-high numbers. Both are indications that more study is needed, and that fish from the Fukushima region can’t yet be pronounced safe to eat. To date, fisheries remain closed in those areas.
The larger health worries are those to be faced on land. As Buesseler explained, “The difference is, on land, once the radiation falls, it stays put, taken up by soils and plants. So you have a long-term source and higher direct exposure to people that doesn’t exist in the ocean, where the radiation is diluted.””
Some fish, referred to as pelagic species, roam the open ocean and can travel across oceans. One such species is the bluefin tuna, which, in addition to being an endangered species due to overfishing, made the news recently when samples of tuna caught off southern California were found to contain radioactivity traceable to Fukushima.   Scientists were excited about this – not because of concern about the radioactivity – but because the radioactivity demonstrated that bluefin tuna do routinely travel all the way across the Pacific Ocean. The amounts the fish carried were minuscule — far less, ounce for ounce, than the amount of naturally occurring radiation in a banana — but enough for scientists to gain insight into animal migration. The detected concentrations of cesium-134 and cesium-137 were well below safety limits set by the most stringent government regulations. But, it’s probably a good thing if this finding gives you another reason to avoid consuming this endangered species. Here's a blog post by Miriam Goldstein at Deep Sea News that further explains why we shouldn't be concerned about the detections of radioactivity in bluefin tuna. A November 2013 article published at oregonlive.com contains further contains additional evaluations of the health risk of consuming West Coast seafood from several scientists in Oregon, including Christina Mireles DeWitt, director of Oregon State’s Seafood Research and Education Center, Delvan Neville, a radiation health physicist at Oregon State, and Kathryn Higley, head of Oregon State’s nuclear engineering and radiation health physics department. Oregon State scientists have continued finding a slight fingerprint of radioactive particles (far too slight to register on a Geiger counter) in local albacore, which migrate throughout the Pacific. Tests on sardines and herring haven’t shown any traces. The levels in albacore are so infinitesimally low, the researchers say, that a person would need to eat 4,000 pounds of albacore a year just to increase their average annual dose of radiation by 1 percent. Fish in the 1980s and 1990s were actually more radioactive because of post-World War II weapons tests than those found today with traces of particles from Fukushima.
The Food and Drug Administration (FDA) screens and tests fish and other imported food from Japan. As of June 20th, 2012, FDA import investigators had performed 32,685 field examinations for radionuclide contamination. FDA had tested 1313 samples, 199 which were seafood or seafood products. 1312 samples had no Iodine-131, Cesium-134, Cesium-137, or other gamma-ray emitting radionuclides of concern. 1 sample was found to contain detectable levels of Cesium, but was below the established Derived Intervention Level (DIL) and posed no public health concern.
Further discussions of the relative health risks from eating North Pacific Ocean seafood is provided in this interview with Ken Buesseler and in this article. Another article discussing this subject appeared on kosu.org in July 2015.
In 2013 and early 2014 articles appeared on several websites and blogs which made rather sensationalist claims that the release of radioactive water into the ocean near Fukushima had already affected sea life (and even human life) along the west coast of the U.S.   Analysis of these claims by scientists has failed to find any connection between radiation releases and West Coast sea life health.      One of the referenced "rebuttals" from Deep Sea News states the following regarding why there is no logical connection between recent incidences of "sea star wasting syndrome" and radiation releases from Fukushima:
Another referenced rebuttal concludes:
California Department of Public Health has monitored air and sand in response to releases of radiation from Fukushima.
In Oregon, the state has created a Japanese Tsunami of 2011 Radiation FAQ that discusses the expected risks from Fukushima radiation and provides links to data from the testing of air, water and sand.
Washington State Department of Health has a similar FAQ.
Japan suffered a terrible disaster and many lives were lost in March 2011 when a large earthquake, a tsunami and a nuclear plant meltdown happened near Fukushima. Understandably, there has been considerable concern about the effects from releases of radiation and, in some cases, continuing exposure. These concerns focus primarily on the workers at the nuclear power plant and for those living in a roughly 20 km “fallout zone” around the power plant. Thankfully, there have been no reported deaths or “deterministic effects” (health problems that include skin burns, eye cataracts, and, in pregnant women, harm to the developing fetus). It does not appear that even the more highly exposed nuclear plant workers experienced these health problems. However, concerns remain that leukemia, thyroid cancer and other longer-term effects will become evident in the coming years. A study by researchers at Stanford University predicted the total cancer casualties (worldwide, but primarily in Japan) that would eventually accrue from the Fukushima nuclear disaster as 130 deaths and 180 additional cancers.
Concern also exists among the general population regarding health effects in the United States from Fukushima releases. Radiation from Fukushima has reached the United States in three ways. Air currents carried radiation across the Pacific to the United States. Radioactive iodine and cesium were detected in air, rainwater, surface water and some food samples collected in California within a few days of the Fukushima disaster. Initial levels, while significantly higher than background, were not considered to represent a human health threat. The levels generally declined to at or near detection levels within about a month after first detection (by mid-to-late April 2011). Cesium was also detected in bluefin tuna caught off the coast of California. These fish had traveled across the ocean from Japan. No cesium was detected in local species such as yellowfin tuna. The amounts detected in the tuna were very low and were not considered to represent a health threat. In June 2013 detectable levels of cesium from Fukushima were measured in ocean water off the coast of British Columbia. However, these concentrations of cesium are less than predicted by most of the plume dispersion models and continue to be well below levels thought to pose environmental or public health threats. No radiation from Fukushima has been detected in marine debris reaching the west coast.
The writers at Deep Sea News have published several articles that address concerns about the human health or ecological impact of radiation releases from Fukushima. This article from January 2014 provides credible information about what is actually occurring and/or dispels myths about Fukushima radiation that are prevalent on the internet. Also see this Scientific American article, this one in the LA Times and this KQED News report. On April 30, 2014 the California Coastal Commission issued a Report on the Fukushima Dai-ichi Nuclear Disaster and Radioactivity along the California Coast. The executive summary of that report concludes:
"The levels of Fukushima-derived radionuclides detected in air, drinking water, food, seawater and marine life in California are extremely low relative to the pre-existing background from naturally-occurring radionuclides and the persistent residues of 20th century nuclear weapons testing. The additional dose of radiation attributable to the Fukushima disaster is commensurately small, and the available evidence supports the idea that it will pose little additional risk to humans or marine life. However, it should be noted that the long-term effects of low-level radiation in the environment remain incompletely understood, and that this understanding would benefit from increased governmental support for the monitoring of radioactivity in seawater and marine biota and the study of health outcomes linked to radiation exposure."
In the following video, Dr. Buesseler of Woods Hole Oceanographic Institution discusses radiation in the ocean and the impacts of Fukushima across the Pacific--from Japan to North America.
Scientific data collected and health studies conducted to date do not provide a basis for concern by residents of the United States regarding short-term or long-term health effects from Fukushima radioactivity releases.
Radiation Health Risks - How can we assess impacts of exposures? (Woods Hole Oceanographic Institution)
Radioisotopes in the Ocean - What's there? How much? How long? (Woods Hole Oceanographic Institution)
FAQ: Radiation from Fukushima (Woods Hole Oceanographic Institution)
Center for Marine and Environmental Radioactivity (Woods Hole Oceanographic Institution)
Radioactice Iodine From Fukushima Found in California Kelp (Scientific American)
How Is Fukushima's Fallout Affecting Marine Life? (Woods Hole Oceanographic Institution)
Tale of the Tuna (Woods Hole Oceanographic Institution)
ABCs of Radioactivity (Center for Marine and Environmental Radioactivity)
Fukushima's Radioactive Water Leak: What You Should Know (National Geographic)
Latest Radioactive Leak at Fukushima: How Is It Different? (National Geographic)
From the special issue of Oceanus Magazine devoted to the cause and impacts of Fukushima:
Fukushima and Ocean Radioactivity by Ken O. Buessler (Oceanography, Volume 27, Number 1, January 2014)