STATE OF CALI FORNI A—NATURAL RESOURCES AGENCYEDMUND G. BROWN, JR., G OVE R NORCALIFORNIA COASTAL COMMISSION
45 FREMONT, SUITE 2000
SAN FRANCIS CO, CA 94105- 2219
VOICE (415) 904- 5200
FAX ( 415) 904- 5400
TDD (415) 597-5885

F10b
April 30, 2014TO:

Coastal Commissioners and Interested Parties

FROM:

Charles Lester, Executive Director
Alison Dettmer, Deputy Director
Joseph Street, Environmental Scientist

SUBJECT:

Report on the Fukushima Dai-ichi Nuclear Disaster andRadioactivity along the California Coast.

Coastal Commission staff has received numerous inquiries on the March 2011 accident at the
Fukushima Dai-ichi Nuclear Power Plant in Japan. Attached for your information is a report
investigating the release of radioactivity materials during the disaster and the implications forresidents of California. Staff’s conclusions are presented in the summary below, and in greater
detail in the attached briefing report.

Report Summary
The Great Tohoku Earthquake and Tsunami of March 11, 2011, led to the partial meltdown ofseveral nuclear reactors at the Fukushima Dai-ichi Nuclear Power Plant, on the northeast coast ofJapan, and to the discharge of large amounts of radioactive material to the atmosphere and theNorth Pacific Ocean. Estimates of the total release range widely, but the accident is generally
recognized as the second largest accidental release of radioactivity in history, after only the
Chernobyl disaster in 1986. Because the Pacific Coast of North America is downwind and“down-current” of Japan, the accident has led to widespread public concern about the prospect ofradioactive contamination along the coast, and, in some cases, the spread of inaccurate or
misleading information. The purpose of this report is to provide the Coastal Commission and thegeneral public with a reliable source of information on the Fukushima disaster, the dispersal ofradioactive materials in the atmosphere and ocean, and the levels of radioactivity detected in
California, based on a review of the best available science.
Several large pulses of radionuclides were released into the atmosphere in the first week after thetsunami, coinciding with explosions and fires in multiple Fukushima reactor buildings. The
atmospheric plume, mostly consisting of radioactive gases and volatile elements, was entrained

by the mid-latitude westerly winds and transported around the Northern Hemisphere. Most of
the atmospheric radioactivity was deposited in the North Pacific or on land areas of Japanthrough rainfall or dry deposition. A small fraction reached the West Coast within 4-7 days of
the accident, resulting in detectable levels of airborne radioactivity in California. Airborne
radionuclides, in particular iodine-131, cesium-134 and cesium-137, were partially transferred to
the land surface through fallout, and were detectable at low levels in soils, surface waters,
drinking water and food products for several months after the accident.
Radioactive fallout to the North Pacific was augmented by the direct discharge of large volumesof radioactive water from the nuclear power plant in the weeks following the accident. Though
the largest releases to the ocean (emergency cooling water used in the damaged reactors) endedin April 2011, on-going leaks from the plant, contaminated river runoff, groundwater leakage
and leaching from nearshore sediments continue to introduce new radioactivity to the ocean near
Japan. Over the last three years, the radioactive ocean plume has been carried eastward by ocean
currents, becoming increasingly diluted as it spreads over an ever-larger area and mixes togreater depths. The leading edge of the plume appears to have reached North America off ofVancouver Island, and could possibly reach California within the next year. However, theconcentration of Fukushima-derived radionuclides (chiefly cesium-137, which has a ~30-yr halflife) is expected to be only slightly above the pre-accident background, and far below that ofnaturally-occurring radioactive elements in the ocean. Radioactive cesium derived from
Fukushima has been detected at low levels in the tissues of highly-migratory fish species such as
Pacific Bluefin tuna, which appear to have accumulated the cesium in their juvenile rearing
grounds in the western Pacific. Cesium has not yet been detected in marine biota local to theeastern Pacific, but some degree of bioaccumulation is likely once the radioactive plume has
arrived along the West Coast.
The levels of Fukushima-derived radionuclides detected in air, drinking water, food, seawaterand marine life in California are extremely low relative to the pre-existing background fromnaturally-occurring radionuclides and the persistent residues of 20th century nuclear weapons
testing. The additional dose of radiation attributable to the Fukushima disaster iscommensurately 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 effectsof low-level radiation in the environment remain incompletely understood, and that thisunderstanding would benefit from increased governmental support for the monitoring ofradioactivity in seawater and marine biota and the study of health outcomes linked to radiation
exposure.

ii

STATE OF CALI FORNI A—NATURAL RESOURCES AGENCYEDMUND G. BROWN, JR., G OVE R NORCALIFORNIA COASTAL COMMISSION
45 FREMONT, SUITE 2000
SAN FRANCIS CO, CA 94105- 2219
VOICE (415) 904- 5200
FAX ( 415) 904- 5400
TDD (415) 597-5885

The Fukushima Dai-ichi Nuclear Power Plant Disaster& Radioactivity in California

Prepared by the staff of the California Coastal Commission
April 30, 2014

This report was prepared by California Coastal Commission staff to provide information about
the Fukushima disaster and to investigate possible effects in California from the radionuclides
released during the accident. This report has not been approved by the Commission.

Fukushima Briefing Report
Report Summary
The Great Tohoku Earthquake and Tsunami of March 11, 2011, led to the partial meltdown ofseveral nuclear reactors at the Fukushima Dai-ichi Nuclear Power Plant, on the northeast coast of Japan,
and to the discharge of large amounts of radioactive material to the atmosphere and into the North Pacific
Ocean. Estimates of the total radiation release range widely, but the accident is generally recognized as
the second largest accidental release of radioactivity in history, after only the Chernobyl disaster in 1986.
Because the Pacific Coast of North America is downwind and “down-current” of Japan, the disaster has
led to widespread public concern about the prospect of radioactive contamination along the coast, and, insome cases, the spread of inaccurate or misleading information. The purpose of this report is to provide
the Coastal Commission and the general public with a reliable source of information on the Fukushimadisaster, the dispersal of radioactive materials in the atmosphere and ocean, and the levels of radioactivity
detected in California, based on a review of the best available science.
Several large pulses of radionuclides were released into the atmosphere in the first week after thetsunami, coinciding with explosions and fires in multiple Fukushima reactor buildings. The atmosphericplume, mostly consisting of radioactive gases and volatile elements, was entrained by the mid-latitude
westerly winds and transported around the Northern Hemisphere. Most of the atmospheric radioactivity
was deposited in the North Pacific or on land areas of Japan through rainfall or dry deposition. A small
fraction reached the West Coast within 4-7 days of the accident, resulting in detectable levels of airborne
radioactivity in California. Airborne radionuclides, in particular iodine-131, cesium-134 and cesium-137,
were partially transferred to the land surface through fallout, and were detectable at low levels in soils,
surface waters, drinking water and food products for several months after the accident.
Radioactive fallout to the North Pacific was augmented by the direct discharge of large volumesof radioactive water from the nuclear power plant in the weeks following the accident. Though the largest
releases to the ocean (emergency cooling water used in the damaged reactors) ended in April, 2011, ongoing leaks from the plant, contaminated river runoff, groundwater leakage and leaching from nearshore
sediments continue to introduce new radioactivity to the ocean near Japan. Over the last three years, theradioactive ocean plume has been carried eastward by ocean currents, becoming increasingly diluted as it
spreads over an ever-larger area and mixes to greater depths. The leading edge of the plume appears tohave reached North America off of Vancouver Island, and could possibly reach California within the next
year. However, the concentration of Fukushima-derived radionuclides (chiefly cesium-137, which has a~30-yr half-life) is expected to be only slightly above the pre-accident background, and far below that ofnaturally-occurring radioactive elements in the ocean. Radioactive cesium derived from Fukushima has
been detected at low levels in the tissues of highly-migratory fish species such as Pacific Bluefin tuna,
which appear to have accumulated the cesium in their juvenile rearing grounds in the western Pacific.
Cesium has not yet been detected in marine biota local to the eastern Pacific, but some degree of
bioaccumulation is likely once the radioactive plume has arrived along the West Coast.
The levels of Fukushima-derived radionuclides detected in air, drinking water, food, seawater andmarine life in California are extremely low relative to the pre-existing background from naturallyoccurring 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 theavailable 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.

2

Fukushima Briefing Report

BackgroundTohoku Earthquake and Tsunami
On March 11, 2011, a magnitude 9.0 earthquake occurred approximately 70 km off the
Pacific coast of the Tohoku region of northern Honshu, the main island of the Japan. The
earthquake, occurring along a 160-km section of the seafloor, triggered a series of massive
tsunamis that struck the coast less than an hour later.
Coastal Commission’s Japan Tsunami Marine
Tsunami run-up heights exceeded 30 m in certain
Debris Cleanup Project
locations, traveled as far inland as 10 km (6 mi) in the
Since January 2013, the Coastal Commission has
city of Sendai, and inundated approximately 561 km2
been partnering with local organizations in each2(217 mi ) of low-lying coastal areas (1, 2). Land
coastal county to conduct volunteer beach cleanups
subsidence (0.3 - 1.2 m) associated with thewith a specific focus on assessing potential tsunami
debris generated by the earthquake and tsunami thatearthquake exacerbated the flooding. Together, thestruck Japan in March 2011. Funded by a grant fromearthquake and tsunami led to over 20,000 casualties
NOAA and the California Office of Emergency
and $200 – 300 billion in infrastructure damage in
Services, these cleanups took place once per quarter
Japan, while the tsunami damaged ports as far awayin each coastal county. Volunteers were given a new
as California, Hawai’i and Chile (2) and generated adata card, developed by Coastal Commission staff
with assistance from NOAA, which highlighted items
large amount of marine debris (see sidebar).
Disaster at Fukushima Dai-ichi Nuclear Power Plant

that had been most commonly reported as potential
tsunami debris. Over the course of 60 cleanups
during 2013, more than 4,700 volunteers collected
debris and data from California’s beaches. While nosingle item was specifically confirmed as tsunami
debris, numerous suspect items were found andreported to NOAA. The Coastal Commission now
has a baseline of data that it will use in the coming
years to compare future cleanup data against in order
to better assess where and when tsunami debris iscoming ashore in California. This information will
help inform the activities of the Commission and the
local emergency responders who may be called upon
to manage large or potentially hazardous items.

The third part of this triple disaster occurred
when tsunami waves arrived at the Fukushima Daiichi nuclear power plant, located on the coast
approximately 150 km southwest of the earthquake
epicenter, about 45 minutes after the earthquake.
Waves of up to 14 m in height overwhelmed theseawall protecting the facility1, inundating much of
the plant and causing the failure of all but one of theplant’s emergency generators (which had come online
when the electric grid failed during the earthquake),
as well as the pumps that provided cooling water to the nuclear reactors (1). With the loss ofboth primary and secondary electrical power, the safety systems designed to protect and cool thefuel in the reactor cores at Units 1, 2 and 3 failed. The reactors overheated, leading eventually tothe melting of nuclear fuels. Hydrogen generated during the accident collected within the reactor
buildings and exploded, exposing the spent fuel pools in Units 1, 3, and 4, leading to a fire in
Unit 4, and venting radioactive gases and volatile elements to the environment. This chain of
events resulted in a massive release of radioactive elements (“radionuclides”) to the atmospherein the days between March 12 and March 18, 2011 (e.g., 3). In the weeks and months that
followed, emergency cooling water used to flood the damaged reactors was discharged directly
to the Pacific Ocean via the NPP’s intake channels, creating a second pathway for the release ofradioactive materials (e.g., 4)1

The seawall was built to withstand a tsunami wave of up to 5.7 m in height (1).

3

Fukushima Briefing Report

Radioactivity Released into the Environment
The Fukushima NPP disaster represents thesecond largest accidental release of anthropogenic
radiation to the environment in history, after only
the 1986 Chernobyl nuclear power plant disaster in
the Ukraine. In contrast to the Chernobyl disaster,which occurred at an inland location, most of theradionuclides released at Fukushima were depositedin the North Pacific Ocean (3, 5, 6), either throughatmospheric fallout or direct discharge. The total
amount of radioactivity released from Fukushima is
not well-constrained, but was far smaller than theamounts released during the atmospheric testing of
nuclear weapons in the 1940s – 1960s. Without
minimizing the magnitude of the Fukushimadisaster, it is important to place the accident in thecontext of the much larger existing sources ofenvironmental radioactivity, including the legacy of
weapons testing and the background radiation
resulting from the decay of naturally-occurring
radioactive elements (e.g., 40K, 238U, etc.) (Figure1). It is also important to understand that the
Fukushima release consisted of multiple
radionuclides with distinct modes of release,chemical properties, radioactive half-lives, andbehavior in the environment, all of which influence
the potential for environmental harm.

Measuring Radioactivity & Radiation Doses
Scientists use a variety of techniques to measure theabundance of radioactive elements in theenvironment, and often express these measurements
in units that are unfamiliar to the general public.
While it is possible to consider radionuclide
abundances in units of concentration (e.g., moles perliter, kilograms per liter), more typically themeasurement techniques used take advantage of thefact that these elements are undergoing radioactive
decay – i.e., the process by which the nucleus of an
unstable atom loses energy by emitting elementary
particles – which can be detected by a variety
specialized instruments. A commonly used unit ofradioactivity is the Becquerel (Bq), which represents
an amount of a radioactive material producing one
atomic decay per second. Units of radioactivity canbe converted to more traditional units ofconcentration using the known radioactive half-life(t1/2) or decay rate of the radionuclide in question.
For the sake of consistency, and in order to match
scientific convention, this briefing paper reports
radionuclide abundances in Becquerel – per cubic
meter (Bq/m3) for air samples; per liter (Bq L-1) forwater samples, and per kilogram (Bq kg-1) for solid
samples (soil, sediment, tissues, etc.).
The radiation dose received by an organism isrelated to the total radioactivity, but must also take
into account the individual radionuclides involved,
which emit different types and amounts of radiation,
and also the mode of exposure – i.e., external sources(e.g., cosmic radiation, CT scan) vs. internal sources(inhalation or ingestion of radionuclides). Radiationdose can be measured as the energy released tobiological tissue through any mode of exposure, or as
the potential for biological damage from someamount of radiation. This latter approach ismeasured in units of Sieverts (Sv), or more often for
low doses, milli-Sieverts (mSv, one thousandth of aSv) or micro-Sieverts (µSv), one millionth of a Sv).
To put this in perspective, one chest x-ray delivers aradiation dose of approximately 0.1 mSv; the averageannual dose in the U.S., from all sources, is 6.2 mSv(19). Figure 2 provides more examples of doses
from various sources.

The primary release of radioactivity to theatmosphere occurred within a week of the accident,
from March 12 – 18, 2011, with subsequent releases
occurring in much smaller amounts. Estimates of
the total atmospheric release range from 11,500 to>20,000 peta Becquerels (PBq, 1015 Bq; see
sidebar), with most of this occurring as xenon-133(133Xe, t1/2 = 5.25 d) and other inert, short-lived
noble gases (3, 7-9). Other radionuclides such as
iodine-131 (131I, t1/2 = 8.0 d), cesium-134 (134Cs, t1/2
= 2.1 yr) and cesium-137 (137Cs, t1/2 = 30.1 yr) werealso released in significant quantities and pose
greater potential risks to human and ecosystem
health due to their reactivity, mobility in the environment, and biological availability. Direct
releases of radioactive water to the ocean trailed the reactor meltdown by several weeks, peaking
in early April, and continuing at lower levels at least through the fall of 2012 (4, 10, 11).
Seepage of groundwater contaminated with high levels of radioactive cesium and strontium-90(90Sr, t1/2 = 28.9 yr) from beneath the plant represents a small but on-going source of radioactivity
to the ocean, while a growing stockpile of contaminated water is being stored on-site at the plant,
4

Fukushima Briefing Reportpresenting a risk of future leakage (12). Direct discharges to the ocean have been dominated by134
Cs and 137Cs, with estimates of the total radioactive cesium input ranging from about 8 to 80
PBq (6). 2
Table 1 provides a list of the primary radionuclides released as a result of the Fukushimadisaster, along with information on their half-lives, estimated abundances, and modes of release.
The range and quantities of radionuclides released were strongly influenced by the specifics ofthe disaster. The Fukushima nuclear accident was characterized by the overheating of reactor
cores, leading to the venting of radioactive gas and to hydrogen explosions, and, separately, fires
in the spent fuel repository of Unit 4. As a result, Fukushima releases were dominated by gases
and volatile fission products (e.g., noble gases, iodine, cesium), with little of the refractory
fission products (e.g., isotopes of neptunium, barium, cerium, ruthenium, etc.) and primary
nuclear fuels (plutonium, uranium) that contributed to the radioactivity released by the
Chernobyl disaster, which consisted of explosions that breached the reactor cores and extensive,
long-lasting fires (6, 14, 15). In the aftermath of Fukushima, the radionuclides of greatest
concern are those which were released in large quantities, are most bioavailable (i.e., easily taken
up by organisms) and/or have long half-lives, allowing them to persist in the environment.
Accordingly, studies of atmospheric deposition have focused on isotopes of iodine (131I, 132I,
133I), tellurium (132Te) and cesium (134Cs, 137Cs), which were most abundant in the initial fallout,and had the potential to affect human populations within days of the accident. The mostabundant radionuclide released at Fukushima, 133Xe, was monitored but presents less of anenvironmental and health concern because it is an inert gas that was not deposited into theenvironment. Studies of ocean radiation, taking into account the relatively long transport times
associated with ocean currents, have focused on 134Cs, 137Cs, and 90Sr, which will persist in theocean for decades to come.
The radioactive isotopes listed in Table 1 are known products of nuclear fission, and arethus, by definition, anthropogenic. Prior to the accident, only longer-lived 137Cs was present in
the atmosphere and ocean in trace quantities, a relic of atmospheric H-bomb testing in the 1950s
and 1960s, and to much lesser degrees, the 1986 Chernobyl disaster and intentional releases fromseveral nuclear reprocessing plants. Detection of the shorter-lived isotopes (e.g., 131I, 132I, 132Te,
134Cs) in atmospheric fallout and ocean water, in addition to elevated activities of 137Cs, provides
incontrovertible evidence of a recent source at Fukushima.
Radioactive materials leaked from the Fukushima NPP have been transported in theenvironment along two main pathways: (1) rapidly, via atmospheric circulation; and (2) slowly,
via ocean currents. A third “biological” pathway, encompassing both human activities andradionuclide transport in the tissues of migratory organisms such as birds or fish, is small relative
to atmospheric and ocean transport, but is of concern to human and ecosystem health. The
following discussion examines each of these pathways and summarizes the best available scienceon the distribution of radionuclides from Fukushima in the environment (with a particular focus
on the California coast), and on the level of risk to humans and marine ecosystems.

2

Buessler (2014) (ref. 6) reports a range of estimates of the total 137Cs discharge to the ocean; here it is assumed that the 134Cs
discharge was roughly the same, based on the widely reported 1:1 activity ratio between these isotopes in Fukushima releases(e.g., 13).

5

Fukushima Briefing Report

Atmospheric Transport & Deposition of Fukushima Radiation
Several massive pulses of radionuclides were released to the atmosphere from Fukushima
between March 12 and 18, 2011, representing the majority of the radioactivity released by thispathway (3, 16). The radioactive plume was rapidly entrained by the strong westerly winds that
dominate at this latitude during the winter, and within days was dispersed and transported
eastward throughout the Northern Hemisphere. Fukushima-derived radionuclides were firstdetected in air samples in western North America on March 15, in Western Europe between
March 19 – 23, and had circled the globe within 18 days of the accident (7, 16-18). The
evolution of the radioactive plume over time was controlled in part by atmospheric circulationand in part by the chemical characteristics of the individual radionuclides. For example, theradioactive noble gas 133Xe (t1/2 = 5.25 d) is inert and does not deposit, and declined relatively
quickly through radioactive decay. Other radionuclides which were abundant in the initial
plume, including radioactive iodine (131, 132, 133I), 132Te (t1/2 = 3.2 d), and three cesium isotopes(134,136, 137Cs) can be dissolved in rainwater or deposited as aerosols, which hastens their removal
and transfer from the atmospheric plume to terrestrial and marine environments. Based on airand precipitation monitoring at Japanese sites (e.g., 16) in comparison to North American sites(e.g., 16, 17, 19-23), and on atmospheric modeling (e.g., 3, 5, 9), most of the Fukushima-derived
radionuclides were removed through rainfall and dry deposition prior to reaching North America(Figure 3). One widely-cited study estimates that as of April, 2011, 18% of the total fallout of137
Cs had been deposited in Japan and 80% in the North Pacific Ocean, with just 2% reachingother land areas (3).
Atmospheric Radioactivity in Western North America
Air & Particulates
Fukushima-derived radionuclides began to be detected at air monitoring stations along
the west coast of North America between March 15 - 18, 2011, three to six days after the
explosions at Fukushima Units 1 – 4 (16, 17, 19, 20, 23-25). Though many real-time monitoring
stations (e.g., EPA’s RadNet network, Health Canada’s Fixed Point Network) were equipped todetect only gross levels of airborne radiation, other stations were equipped to test for specificradionuclides at very low concentrations 3, including 131I, 132I, 132Te, 134Cs, 137Cs, and in a few
locations, 133Xe and other radioactive noble gases (17, 20, 26). Measured peak concentration ofthese radionuclides ranged widely, but in general were hundreds or thousands of times lower
than those measured at Japanese stations near Fukushima.
The largest single component of the airborne radioactive plume to reach North America
was 133Xe, but as noted above, this noble gas is inert and poses little risk because it is notabsorbed by the body or the environment (8, 20). Levels of 133Xe in air samples from Canada
and the United States declined steadily after a peak in late March, 2011, and had dropped below
detection limits by the end of May (17, 20, 26). Peak airborne concentrations along the West
Coast of the other, more hazardous radionuclides 4 in the weeks following the accident fell within
3

Including a subset of the U.S. EPA’s RadNet stations, Comprehensive Nuclear Test Ban Treaty monitoring stations in the
United States, Canada, and Pacific Islands, Oregon Health Authority station in Portland, and a handful of stations operated byacademic institutions.
4
Most air monitoring stations with individual radionuclide capability reported elevated levels of 131I, 132I, 132Te, 134Cs, and 137Cs
in the first few weeks following the accident; other radionuclides reported less frequently, and at far lower levels, at the moresensitive stations included 136Cs, 129Te, 140La, 99mTc, 140Ba, and 133I.

6

Fukushima Briefing Report

the range of 7 – 104 mBq/m3 (0.016 – 0.104 Bq/m3), with much (40-100%) of the total
attributable to 131I (19).
In California, peak values in air samples were detected on March 17-18 in San Francisco
and Berkeley (31 - 35 mBq m-3), March 21 in Anaheim (70.3 mBq m-3) and March 22 in San
Bernardino (40.7 mBq m-3) (19, 23). Airborne concentrations of radionuclides dropped quickly
after March 2011, and, with the exception of longer-lived 134Cs and 137Cs, were generally
undetectable within six weeks of the accident (e.g., 17, 19, 24, 25). 134Cs and 137Cs persisted at
trace levels (~1000 times below peak values) in on-going air monitoring at Berkeley through theend of 2012 (23).
Precipitation
Wet deposition in precipitation is the primary means by which Fukushima-derived
radionuclides have been removed from the atmosphere, as documented by detection of fission
products in rainfall occurring in Japan, North America, and Eurasia in the weeks following thedisaster (e.g., 17, 21, 27, 28). 131I, 134Cs or 137Cs from Fukushima were detected at ~20% of 167
sampled National Atmospheric Deposition Program (NADP) monitoring sites in the UnitedStates between March 12 – April 5, 2011, including at four of twelve sites in California (21).
March 2011 was an unusually wet month in California (~200% of normal monthly precipitationin the Bay Area) due to several large storms which resulted in discrete wet deposition events on
March 18-20 and 22-26. Radionuclide activities measured in precipitation from these storms atvarious California locations ranged from about 2 – 20 Bq/L for 131I, the most abundant isotope
detected, and 1-2 orders of magnitude lower (~0.03 – 1.4 Bq/L) for 132I, 132Te, 134Cs, and 137Cs(19, 21-23). 5 More extended sampling at Oroville and Richmond demonstrated that radionuclide
concentrations in rainfall declined rapidly
Governmental Limits on Radionuclides
beginning in early April, and that only 134Cs
137
in Food & Drinking Water
and Cs were present, at low levels, after 70
U.S. EPA Drinking Water Maximum Contaminant Levels
days (19, 23). However, it is worth noting that
low levels of radioactive cesium (<0.01 Bq/L)• 0.04 mSv/yr Gross beta & photon radiation *were still detectable in rainwater during• 0.56 Bq/L
Gross alpha radiation #subsequent wet seasons in 2012 and 2013 (23),*dose-based limit, equivalent to ~3 Bq/L of 131I, 134Cs or 137Cs
reflecting the continued presence of#No alpha emitters were detected in the U.S. following the
Fukushima-derived cesium in the atmosphere.
Fukushima disaster
Surface Waters, Soil & Food
Fukushima-derived radionuclides
transferred from the atmosphere to the landthrough rainout or dry deposition have thepotential to contaminate soil and watersupplies, and to enter the food chain. Evidenceof this is seen in reports from Japan
documenting contaminated soils (28, 29),
surface waters (28, 30) and food products (e.g.,31) in the areas surrounding Fukushima. Other
studies have explored impacts to wildlife andU.S. FDA Derived Intervention Limits for Food•

170 Bq/kg

Iodine-131 (173.9 Bq/L, milk)•

1200 Bq/kg

Cesium-134 + 137 (1221 Bq/L, milk)•

160 Bq/kg

Strontium-90 (162.8 Bq/L, milk)

Revised Japanese Limit on Radiocesium in Seafood•

100 Bq/kg

Cesium-134 + 137

Sources: U.S. EPA (64); U.S. FDA (38); Japanese Ministry ofAgriculture, Forestry and Fisheries (56)5Radionuclides were detected in precipitation at: NADP monitoring stations located in Yosemite and Pinnacles National Parks,
and San Bernardino and Los Angeles Counties; the EPA monitoring station in Richmond; and UC Berkeley/LBNL monitoring
stations located in Berkeley, Oakland, Albany and Oroville.

7

Fukushima Briefing Reportecosystems; findings include elevated levels of radioactive cesium in plant and animal tissues(32-34), reduced bird populations (35) and physiological and genetic damage in butterflies living
near the nuclear plant (36). As discussed above, concentrations of radionuclides in air and water
samples in California were orders of magnitude lower than in Japan, limiting, in theory, thepotential for dangerous levels of contamination on the land surface. This prediction is largely
borne out in the available data, though surprisingly little research effort has been devoted to thisissue in California.
Researchers at UC Berkeley (BRAWM, RadWatch) have undertaken one of the few“vertically integrated” studies of Fukushima radionuclides in the environment, including
measurements in air, rainfall, surface and drinking water, soil, plants, and food items in Northern
California (22, 23, 37). This sampling effort detected minute quantities of 131I and 137Cs (≤ 0.1
Bq/L) in Berkeley tap-water and runoff in a local creek between March 25 – 30, 2011, but
nothing thereafter. Perhaps more importantly from a statewide perspective, no Fukushimaradionuclides were detected in snowmelt runoff to Hetch Hetchy reservoir, in the central Sierra
Nevada, in June 2011. Sampling of soil and sediments from several California locations 6
detected a clear pulse of 131I, 134Cs and 137Cs between April – June 2011, with only 137Cs
remaining above the pre-accident background thereafter (through Nov 2012). Plant and foodsamples 7 collected in the Bay Area in April and May 2011 contained detectable concentrationsof Fukushima-derived 131I, 134Cs, and 137Cs, indicating that low-level contamination of the waterand soil had worked its way into local ecosystems (19, 23, 37). However, in all cases, theradionuclides were detected at levels many times below those of naturally-occurring radioactive
isotopes (e.g., 40K, 210Pb, 7Be) and applicable health limits. For example, measured levels of
Fukushima-derived radioactivity in Bay Area milk samples (1.4 – 2 Bq/L, mostly 131I, 134Cs,
137
Cs ) was still 25 times lower than that attributable to naturally-occurring potassium-40, andhundreds of times lower than the U.S. FDA’s “intervention levels” for iodine-131 (174 Bq/L)
and radiocesium (1221 Bq/L, 134+137Cs) (38). 8 Moreover, the detectable contamination appears
to have been short-lived: Fukushima-derived radionuclides were not found in Bay Area foodproducts after May, 2011 (19, 23, 37).
Fukushima Radiation in the Ocean
Over the long term the radioactive signature of the Fukushima accident can be mostclearly read in the waters of the North Pacific Ocean. A large fraction of the initial atmosphericrelease of radionuclides was transferred to the North Pacific through wet and dry deposition in
the days following the accident (3, 5), so much so that airborne concentrations of radioactive
cesium-134 and -137 in North America were orders of magnitude lower than those measured inJapan just a few days earlier (Figure 3). Radionuclides also reached the sea via the directdischarge of cooling water from the plant, along with surface run-off and groundwater seepage
from contaminated areas of the power plant site. Direct discharges to the ocean began at the endof March 2011, peaked in early April, and continued in smaller amounts at least through the fallof 2012 (4, 10, 11, 13). In addition, river runoff and groundwater discharge from contaminated6

Topsoil from Oakland, Alameda, Sacramento, San Diego, and Sonoma County; sand from Palo Alto; roadway sediment fromBerkeley.
7
Products tested included milk, yogurt, strawberries, spinach, kale, wild mushrooms, cilantro, arugula, carrots, and tomatoes.
8

FDA derived intervention levels reflect allowable concentrations in food products based on the radiation dose received fromconsuming the product over one year, and a tolerance threshold of two additional cases of cancer per 10,000 people.

8

Fukushima Briefing Reportareas, along with seafloor sediments off of Fukushima, are expected to supply relatively small
but continuing doses of radioactivity to the North Pacific for years to come (6, 39, 40).
In comparison to atmospheric circulation, which within days dispersed radioactive
materials over large areas of the globe, ocean currents move slowly; in the three years since theaccident, Fukushima-derived radionuclides have spread throughout the North Pacific, but are justbeginning to arrive along the North American coast (41). The great size and relatively slow
circulation of the Pacific have at least two important implications for the spread of radioactivity
in the wake of the disaster: First, radioactivity released from Fukushima to the ocean has beenmassively diluted. Second, in the years since the disaster, radionuclides with short half-lives(e.g., 131I) have been removed through radioactive decay, leaving behind only a fraction of thetotal radioactivity initially deposited in the ocean in the form of longer-lived radionuclides,
chiefly 134Cs (t1/2 = 2.1 yr) and 137Cs (t1/2 = 30.1 yr). 9 Radioactive cesium persists in the ocean
for long enough to be transported significant distances by ocean currents. The total input of137
Cs to the North Pacific from Fukushima are poorly constrained, with estimates ranging from14 – 90 PBq; estimates of the direct ocean discharge range from 4 to 41 PBq, with most in therange of 10-15 PBq (6). For comparison, total 137Cs releases from the Chernobyl disaster wereon the order of 100 PBq (of which ~20% reached the ocean), while global fallout from nuclear
weapons testing was approximately 950 PBq (with ~76 PBq still present in the North Pacific in2011) (Figure 1) (6).
Based on this calculus, in the worst case the Fukushima disaster approximately doubled
the amount of 137Cs in the North Pacific, and given that 134Cs and 137Cs were released from
Fukushima in an approximate 1:1 ratio (13), may initially have tripled the total amount ofradioactive cesium in the North Pacific (134Cs, with a two-year half-life, decays much more
quickly than 137Cs). However, in order to place the radiocesium release from Fukushima to the
Pacific Ocean in the proper context, it is important to understand that the oceans are naturally
radioactive, with an average background activity of ~14 Bq/L. 10 Approximately 93% of thisbackground radioactivity is produced by naturally-occurring radionuclides (mostly potassium-40,
40K) derived from the rock weathering and the erosion of continental crust. The remainder,
about 7% (~1 Bq/L), is anthropogenic, deriving mostly from fallout from atmospheric nuclear
weapons testing, but also from the Chernobyl accident and discharges from nuclear fuelreprocessing plants. The background activity of 137Cs in the North Pacific prior to Fukushima
was 0.001 – 0.002 Bq/L; after 10 years, when model simulations indicate the cesium will havespread more or less evenly throughout the entire ocean basin, basin-wide 137Cs concentration
may double (to 0.002 – 0.003 Bq/L) due to the accident (45, 46), but would still only amount to atiny fraction of the total radioactivity of the ocean.

9

Other long-lived nuclear fission products of potential concern include isotopes of strontium (90Sr, t1/2=28.9 yr) and plutonium(
Pu). The Fukushima disaster resulted in the release of radioactive strontium, which was detected in the ocean but at
levels <3% of the measured 137Cs in the same samples (42). 90Sr is much more difficult to measure than cesium, but because its
chemical behavior is similar to that of calcium, it is highly biologically-available. Though a very small amount of plutonium may
have been released to the atmosphere and deposited near the accident site (43), no Pu isotopes have been detected in seawater orsediments off of Japan (44).
10
In the scientific literature, ocean concentrations of radioactive materials are typically reported in units of Bq/m3, reflecting both
the relatively low concentrations of radionuclides in the ocean and the large volume samples often needed to make themeasurements. This report uses Bq/L because the liter is a familiar quantity for most readers, and to ease the comparison withlevels of radioactivity in precipitation, drinking water, etc. Concentrations in Bq/L can be converted to Bq/m3 by multiplying by
1000.
238, 239, 240, 241

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Fukushima Briefing Report

In summary, though the Fukushima disaster transferred a massive amount of radioactive
material to the ocean, on par with the worst nuclear accidents in history, in aggregate theadditional radioactivity added is small compared to both the natural inventory and the legacy of
20th century nuclear weapons testing.
Spread of Fukushima Radioactivity into the North PacificApproximately 99% of the direct discharge of radioactivity to the ocean from Fukushima
took place in the initial aftermath of the accident, when cooling waters that were used to flood
the damaged reactors were discharged to the artificial harbor area immediately seaward of thenuclear power plant (11). In early April, 137Cs concentrations in the discharge channels of theplant peaked at more than 50 million times greater than the pre-existing ocean background (13).
These high volume, high concentration discharges slowed greatly after April 6 when TEPCO
succeeded in stopping leaks from the damaged reactor units, but low-level discharge ofradioactive water, enough to maintain elevated (1 – 10 Bq/L) cesium concentrations off of theplant, continued at least through the fall of 2012 (11, 47). On-going seepage of contaminatedgroundwater to the ocean has also been detected (12). The open nature of the Fukushimacoastline results in the rapid flushing of discharged water and radionuclides away from the coast(15).
Together with atmospheric fallout, most of which occurred over the ocean to the east ofJapan (3), the directly-discharged radionuclides formed a plume of radioactive surface water that
was advected into the open North Pacific by the strong, eastward flowing Kuroshio Extension
current (Figure 4). In June 2011, four months after the accident, the plume had spread eastward
up to 600 km throughout the “mixed layer” (upper ~150 m) of the ocean, but had not yet
penetrated into deeper waters (10). 134Cs concentrations between 30 and 600 km offshore ranged
from 0.1 – 3.9 Bq/L, with the highest values measured in semi-permanent eddies of the Kuroshio
Extension southeast of Fukushima. Interestingly, the Kuroshio Current system appears to have
served both as a conduit for the eastward transport of the radioactive plume and as a barrier tosouthward transport – in the western North Pacific, the surface plume was essentially trapped
within and north of the current (10, 48), directing the spread of the plume toward North America
rather than Asia or Oceania.
In the months and years following the disaster, the radioactive plume continued to spreadeastward into the central North Pacific (e.g., 41, 47, 48, 49, 50). Beyond coastal Japan,
measurements are sparse, and generally not sufficient to delineate the boundaries of the plume inthree dimensions, but its general eastward progress can be tracked, and the measured
concentrations of 134Cs and 137Cs compared with the predictions of several model simulations ofplume evolution (46, 51, 52) (see Figure 4). By the winter of 2012, the leading edge of theplume at ~40º N latitude had crossed the International Dateline (180º E longitude), with anestimated rate of spread of about 8 cm/s (~4 mi/d) and a peak combined 134+137Cs concentrationof 0.02 Bq/L. (47, 49). Though still elevated above the pre-accident background, this value ismore than 3 million times lower than peak concentrations measured immediately offshore of
Fukushima in April, 2011 (13), providing some idea of the degree of dilution, radioactive decay,
and cesium removal (e.g., through adsorption to sinking particles) that had occurred to that point.

10Fukushima Briefing Report

Arrival on the West Coast
The most recently reported measurements of radioactive cesium in North Pacificseawater indicate that the Fukushima plume is beginning its arrival off the west coast of North
America. Measurements by the Canadian Ocean Monitoring Program first detected very low
concentrations (<0.0005 Bq/L) of Fukushima-derived 134Cs at a station in the Gulf of Alaska(~145º W) in June of 2012, and off of Vancouver Island, British Columbia, in June 2013 (41).
This early arrival, scarcely three years after the accident, matches well with the predictions of
one ocean circulation model (52), but the low concentrations detected are more in line withanother simulation that predicted a slower transit of the North Pacific (46). Further to the south,along a transect approximating 30º N latitude, shipboard sampling found that in late 2013 theleading edge of the cesium plume was north of Hawai’i, between 160 – 150 ºW, but thatconcentrations were relatively low (≤ 0.008 Bq/L), well below those predicted for this area(>0.05 Bq/L) by the more spatially-accurate model (50, 52). The lower-than-expectedconcentrations observed in situ may reflect the fact that a large fraction of the radioactive plumethat occupied the central North Pacific in 2012 was mixed into the deep ocean and effectively
removed from the eastward-trending surface plume (48).
To date, no Fukushima-derived cesium has been detected in seawater along the coast of
California, Oregon or Washington (24, 37, 50). 11 It remains uncertain exactly when, and at what
concentration, the radioactive plume will reach the California coast, though the recent detectionof cesium off of British Columbia provides some indication that this could occur within the next
year. However, the model simulation of Rossi et al. (2013) (52), which came the closest tocorrectly predicting the timing of the plume arrival in the Pacific Northwest, also predicts that
offshore currents associated with coastal upwelling in the California Current system could delay
the arrival of the plume on the California shoreline for several years. Under this scenario, theradioactive plume would be “held at bay” by the net offshore transport of surface water, only
reaching the coastline proper once the cesium has penetrated to the depths of the waters that are
upwelled along the coast. Once the radioactive plume does reach California, concentrations ofradiocesium are predicted to increase to peak values between 2016 and 2019, declining gradually
thereafter over the next several decades (46, 52). The actual concentrations remain unknown
but, based on recent measurements elsewhere in the North Pacific, are likely to be on the lower
end of the 0.003 – 0.02 Bq/L range bracketed by the predictions of Behrens et al. 2012 (46) andRossi et al. 2013 (52), respectively (41, 50). It is important to note that even the higher estimatedlevels of radioactivity are dwarfed by naturally-occurring radioactivity (>400 times greater) andthe 137Cs “legacy” of atmospheric nuclear weapons testing (>30 times greater), and represent
only a tiny increase in total radioactivity above the pre-accident background.
Fukushima Radioactivity in Seafood & the Marine Ecosystem
Generally speaking, levels of radioactivity in marine organisms will be proportional to
the radioactivity of the water in which they live, with higher levels expected in organisms
dwelling closer to the source of contamination. However, certain radionuclides which arechemically similar to nutrient elements can be preferentially absorbed by marine organisms andbecome concentrated in the marine food web. Strontium-90 (90Sr), for example, mimics the11
Cesium-137 derived from atmospheric fallout of nuclear weapons tests in the 1940s-1960s is still present, at very low
concentrations, in the world ocean. Recent measurements off the California place the “background” level of 137Cs at 1.3 – 1.9
Bq/m3 (50).

11

Fukushima Briefing Reportchemical behavior of calcium, and if taken-up by organisms is concentrated in calcium-rich
structures such as shell and bone, where it delivers a sustained dose of radiation over time.
Cesium is also highly bioavailable, but is distributed more evenly throughout the body and isremoved more quickly (“biological half-life” of ~ 70 days in humans) (53).
Impacts to marine life from the Fukushima disaster are most evident in the coastal ocean
nearby the nuclear power plant. Fish caught in the Fukushima area, in particular bottomdwellers which may be exposed to high radionuclide concentrations in seafloor sediment, have
had levels of radioactivity well above the Japanese regulatory limit of 100 Bq/kg (in an extreme
case, >100,000 Bq/kg) (54, 55, 56). In 2011 alone, the closure of local fisheries is estimated tohave resulted in $1 – 2 billion in economic losses (54). Other species, with different life
histories and occupying different ecological niches, were less consistently contaminated (or atlower levels), and a few appear to have escaped contamination entirely (e.g., squid, octopus) (54,56). Sampling in June 2011 at locations 30-600 km offshore of Fukushima prefecture found total
radioactive cesium (134+137Cs) levels of 0.3 – 102 Bq/kg in zooplankton and fish (below the 100
Bq/kg limit in all but one case) (10).
Along the West Coast, Fukushima-derived radionuclides were fleetingly detected in giant
kelp off of California (131I) (57) and in Alaskan salmon (trace amounts of 134Cs and 137Cs) (58),reflecting the “pulse” of atmospheric fallout immediately after the accident. Subsequent
sampling of kelp and fish local to the eastern North Pacific has not detected further
contamination (37, 58, 59). However, a study by Madigan et al. (2012) demonstrated thepotential for highly-migratory species, in this case Pacific Bluefin tuna, a species that spawns
and rears in the western Pacific, to transport radionuclides over long distances. Pacific Bluefin
tuna caught off of California in August 2011 contained an average of 10 Bq/kg of radioactive
cesium (134+137Cs) from Fukushima, which the fish accumulated in contaminated western Pacificwaters prior to migration (59). 12 A 2012 follow-up study found that radiocesium levels in
Pacific Bluefin had decreased by more than 50% (60).
When the plume of radioactivity currently spreading across the North Pacific reaches theCalifornia coast, local marine life will accumulate Fukushima-derived radioactive cesium (andother radionuclides present at much lower levels, such as 90Sr). The low radiocesium
concentrations currently observed in seawater off of British Columbia (41) and in the central
Pacific north of Hawaii (50) suggest that the level of exposure will be quite low, and that marineorganisms are unlikely to accumulate dangerous quantities of radioactivity. However, on-going
monitoring of the situation is clearly warranted.
Risks & Health Implications of Fukushima Radiation
It is clear from the available data that people living on the West Coast were exposed to
Fukushima-derived radiation in the days and weeks following the disaster, with lower levels of
exposure (from radioactive cesium) continuing to the present. Environmental and public healthagencies at the state and federal levels have issued repeated assurances that the levels of
exposure are “safe”, “not harmful” or present “no risk” to the public (e.g., EPA RadNet, Oregon
Health Authority, etc.), often citing regulatory standards or exposure limits that are higher than12

For comparison, post-accident concentrations of 134+137Cs in Pacific Bluefin caught off Japan were in the range of 61-168
Bq/kg, 6-17 times higher than those caught off California (56, 59).

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Fukushima Briefing Report

the measured levels of Fukushima-derived radiation. Though the basic message is likely to beaccurate, such assertions are probably best read as “shorthand” for a more nuanced reality: The
levels of Fukushima-derived radiation detected in North America are unlikely to causesignificant harm to the public at large, and the risks posed by Fukushima radiation are small incomparison to other things that threaten public health (e.g., air pollution, smoking, obesity, etc.)(53). This more circumspect assertion of safety does not rule out adverse impacts to individuals,
and more accurately reflects the current level of scientific uncertainty about the health risks oflow levels of radiation. Individual risk is influenced by multiple factors, including the strengthand length of exposure, the particular radionuclides involved, and the age, health andsusceptibility of the individual, to name a few. Moreover, the health effects of long-term
exposure to low-level radiation are a matter of on-going scientific debate. The canonical,
precautionary view, which extrapolates from studies of the health impacts of high doses ofradiation, is that any increment of increased radiation exposure, no matter how small, increases
an individual’s chance of developing cancer or other health problems, and that even unavoidable
natural background radiation can contribute to health problems (53). However, the relationshipbetween radiation dose and health consequences has not been established for doses below 100
mSv, and studies on animals indicate that much of the DNA damage done by low-level radiation
can be undone by natural DNA-repair mechanisms in the body (61).
WHO Study
The World Health Organization (WHO) has attempted to estimate radiation doses from
Fukushima to people living in Japan and other parts of the world, using both observations andmodeling approaches (8). The resulting study considers the full range of exposure pathways,
including external doses from radioactive contaminants in the atmosphere (“cloudshine”) anddeposited on the ground (“groundshine”), as well as internal dose from the inhalation andingestion of contaminated air, food, and water. Within Fukushima prefecture, radiation doses
from the accident were estimated to range from 1 – 200 mSv, depending on an individual’s age,body-size and geographic location. Elsewhere in Japan estimated doses ranged from 0.1 – 1
mSv. Outside of Japan, the total radiation dose attributable to the Fukushima disaster was
estimated to be less than 0.01 mSv (8). To put these numbers in perspective, the average annual
dose in the United States prior to the accident, from all sources (e.g., natural background, bomb
testing legacy, medical procedures), was 6.2 mSv (19). Doses from a number of sources ofradiation are shown in Figure 2. The WHO analysis indicates that, outside of areas in close
proximity to the nuclear power plant, the increase in radiation dose as a result of the accident wasvery small.
Radiation Exposure in California
Local-scale analysis of radiation exposure in California seems to bear out this finding.
For example, if a person were to breathe the most radionuclide-contaminated air detected in
California (single-day peak of 70.3 mBq/m3 in Anaheim, 3/21/11) and the tap-water with thehighest sampled level of radioactivity (0.09 Bq/L, Berkeley, 3/30/11) for an entire year, he would
receive an additional dose of about 5 µSv (0.05 mSv), or less than 0.1% of the average annual
radiation dose prior to the accident. 13 Given that these were peak values, not representative of
13

Dose calculations follow the methodology of BRAWN (2011) (37).

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Fukushima Briefing Report

air and drinking water over the full year, the actual dose received by Californians from breathing
and drinking in the aftermath of the Fukushima disaster was almost certainly much lower.
Radiation doses in food are more difficult to estimate due to the wide variety of plant andanimal products, sourced from various parts of the world, that are included in the typical
American diet. A person consuming certain groundfish species or other embargoed foodproducts from the area around Fukushima risks exposure to potentially dangerous levels ofradiation, but these foods are difficult to acquire for the average Californian. 14 Fukushimaderived radionuclides were detected at low, but variable levels in locally-produced foods in
California in the weeks after the accident (23, 37), but as with the cases of air and drinking
water, it would take consuming the most contaminated of these foods, at their peak levels ofradioactivity, for long periods of time to accumulate even a modest dose of Fukushima-derived
radiation. For example, a recent study examined the radiation exposure of a hypotheticalsubsistence fisherman consuming only Pacific Bluefin tuna in amounts five times greater than
the average total seafood consumption in the U.S. Based on observed levels of Fukushimaderived cesium in Pacific Bluefin tuna (~10 Bq/kg of 134+137Cs), such a fisherman would receive
a 4.7 µSv (0.0047 mSv) radiation dose in a year, or 0.1% of the average pre-accident annual dose
(55).
External doses of radiation from the environment (cloudshine and groundshine) in places
outside of Japan were very small in relation to internal doses (8), and thus are not expected to
add much to an individual’s total radiation dose. Likewise, radiation doses from contact withseawater will also be extremely low due to low radionuclide concentrations expected off the
California coast (<0.02 Bq/L) (46, 52) and the fact that even the most vulnerable populations(e.g., surfers, fishermen, etc.) spend only a minor fraction of their time in the ocean. In summary,the radiation dose to Californians from the Fukushima disaster is very unlikely to amount tomore than a few percent of the average annual dose from the natural background andanthropogenic sources, and overall the Fukushima disaster presented (and continues to present) a
low risk to public health relative to other concerns. However, it is worth reiterating that thehealth implications of exposure to low levels of radiation remain incompletely understood, andthat the incremental impacts of the radiation released at Fukushima may be very difficult toseparate from those of other radiation sources (e.g., bomb-testing legacy) and the many othercauses of disease (61).
On-Going Monitoring Efforts
Existing, government-supported environmental monitoring networks appear to have
performed reasonably well in the immediate aftermath of the Fukushima Dai-ichi nuclear
accident. Air and precipitation monitoring networks managed by the U.S. Environmental
Protection Agency (EPA RadNet) 15 and Health Canada detected arrival of the atmosphericplume, and increased their regular sampling frequency for several weeks to months in order todocument the declining levels of atmospheric radioactivity as the plume was dispersed and
14
U.S. FDA has banned certain food products from being legally imported into the United States from Japan (62). The WHO hastested thousands of Japanese food products that continued to be exported after Fukushima, and found detectable levels ofradionuclides in only a small handful of samples (8).
15
EPA’s RadNet network includes 100 stations nationwide, including 11 in California, for the monitoring of radiation in air,
precipitation, milk and drinking water.

14

Fukushima Briefing Reportindividual radionuclides were removed through fallout and radioactive decay. These federal
agency efforts were supplemented by monitoring undertaken by national laboratories (e.g., 23,
26, 37), state governments (e.g., 24), academic institutions (e.g., 22, 23, 37, 58), andgovernment-university partnerships (e.g., 21) at other locations, cumulatively providing a fairly
detailed view of atmospheric fallout following the accidents. Many of these monitoring
programs are on-going, and can be expected to detect and quantify and future large-scale releasesof radiation to the atmosphere.
Radioactivity in drinking water and food products is also routinely monitored, withlimited frequency, as part of the EPA RadNet program. In California, the EPA tests forradioactivity in drinking water and milk at least several times a year in Los Angeles and the Bay
Area. EPA’s sampling frequency temporarily increased in the months following the Fukushimadisaster. While it does not itself measure radioactivity in imported foods, the Food & Drug
Administration (FDA) maintains a list of Japanese food products subject to detention (Import
Alert 99-33), which is informed by radiation testing conducted by the Japanese government (62).
A limited amount of testing of food and drinking water was also performed by academic
researchers in the first two years following the accident, but many of these efforts have ended orwere never intended as comprehensive monitoring programs (e.g., 23, 58, 59).
Outside of Japan, ocean monitoring of Fukushima radiation has received much lessattention and support from government agencies. Though the Canadian government is actively
monitoring for the arrival of the radioactive cesium plume off the coast of British Columbia, andthe state of Oregon is collecting seawater samples at several coastal locations, neither the U.S.
federal government nor the state of California is currently testing for Fukushima-derived
radiation off the California coast. Instead, most of what we know about the spread of theradioactive plume in the North Pacific is due to the efforts of a handful of academic researchers,
a sub-set of whose work is cited in this report. At present, the only network for monitoring
ocean water along the California coast is a citizen-science effort spearheaded by Dr. Ken
Buessler of the Woods Hole Oceanographic Institution, to date consisting of 11 sampling stations
spread between San Diego and Trinidad, with samples collected by volunteers (the network also
includes sites off Oregon, Washington, British Columbia and Alaska) (50). A similar effort tomonitor radionuclide levels in kelp along the Pacific coast (including 32 sites in California) is
being led by Steven Manley (CSU-Long Beach) and Kai Vetter (UC Berkeley) (63). These
efforts are critical for monitoring the spread of Fukushima radioactivity along the coast, forunderstanding the degree to which radionuclides enter and affect marine ecosystems, and for
confirming the expectation that radionuclide concentrations will remain below levels of healthconcern. In light of the high level of public concern surrounding the effects of the Fukushimadisaster on marine ecosystems and on-going confusion about the risks posed to human health, agreater level of involvement in coastal ocean monitoring by government resource management
agencies would be desirable, particularly in light of the somewhat precarious dependence of theexisting academic and citizen-science monitoring programs on volunteers and occasional funding
sources (e.g., sponsors, grants) (50, 63).

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Fukushima Briefing Report

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Table 1: Selected radionuclides released during the Fukushima Dai-ichi nuclear accident.
Radionuclides discussed in this report are highlighted in bold. Blank cells indicate alack of data rather than no release.

Radionuclide

Xenon-133

133

Iodine-131

131

Xe
I

Half-life(t1/2)

Environmental
Characteristics(phases, behavior,mode of release)

Estimated
Release(atmosphere)
PBq

Estimated
Release(ocean – directdischarge)
PBq

5.25 dinert gas
atmospheric release

5,950 – 20,000

n/aIodine-132

132

2.3 hrIodine-133
Iodine-135
Tellurium-132

133

20.8 hr
6.6 hr3.26 dOther tellurium

I

I
135
I
132
Te
127m
Te
129m
Te
131m
Te

1 – 109 d
2.1 yrCesium-134

134

Cesium-136

136

Cs

13.2 dCesium-137

137

Cs

30.1 yr

Strontium-89

89

Sr

5.5 d

Strontium-90

90

Sr

28.9 yr

Barium-137(metastable)

Barium-140
Cerium-141
Cerium-144
Ruthenium-103
Ruthenium-106
Plutonium-239
Plutonium-240

Cs

137m

Ba

2.6 min

140

Ba
Ce
144
Ce
103
Ru
106
Ru
239
Pu
240
Pu

12.8 d32.5 d285 d39.3 d
1.02 yr
24,110 yr
6,561 yr141

106 – 380

8.0 dparticulate, gas phases
volatile
atmospheric releaseparticulate
somewhat volatile
atmospheric releaseparticulate
somewhat volatilewater solublebioavailable
atmospheric release &direct discharge

0.013 – 56.4

particulate,refractory
particulate,refractory
particulate,refractory#4 – 40#

3.8 – 9.8

particulate, refractorybioavailable
direct discharge
particulate,refractory8

9.4 x 10-14

6 – 503, 7, 8, 9(& refs. therein)
7, 8, 9(& refs. therein)
8, 9(& refs. therein)

42.1
2.27
88.0

16.5 – 50#

References

3.6 – 410.09 – 0.9

6, 8, 9(& refs. therein)
9(& refs. therein)
3, 5, 6, 7, 8, 9(& refs. therein)42

4.1 x 10-4

9

3.13
0.018
0.013
7.5 x 10-6
2.1 x 10-6

8

trace quantities

43, 448
8

The range of release estimates for 134Cs includes both direct estimates and inferred amounts assuming a 1:1 ratiowith 137Cs (e.g., 10).

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Fukushima Briefing Report

Figure 1: Comparison of the inventories of two common natural radionuclides in the ocean,potassium-40 and uranium-238, with anthropogenic cesium-137 from several different sources.
Inventories are calculated for the entire ocean for the natural radionuclides, and at time ofdelivery for cesium-137. One PBq = 1015 Becquerels. Reproduced from Buessler (2014) (6).

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Figure 2: Estimated radiation doses (in micro-Sieverts) from a variety of radiation sources andscenarios. Doses relevant to exposure from Fukushima-derived radionuclides in
California are circled. Sources are indicated in parenthesis.

* Dose calculated in this study based on the methodology of BRAWN (37).

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Fukushima Briefing Report

Figure 3: Estimated total deposition of cesium-137 (MBq/km2) onto Japan and the western
North Pacific Ocean in the month following the Fukushima disaster. Based on
observations and modeling. Reproduced from Yasunari et al. (2011) (29).

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Figure 4a (above): Model simulation of the evolution of the Fukushima-derived radioactive
surface water plume (shown as activity concentrations of cesium-137) in the North
Pacific in (a) April 2012, (b) April 2014, (c) April 2016, (d) April 2021, and (e) along
37.5º N latitude. White flow vectors (arrows) illustrate the large-scale surface
circulation at various locations. Reproduced from Rossi et al. (2013) (52). Ocean
monitoring results indicate that the simulated concentrations of radioactive cesium
shown in the figure are overestimates, and that actual concentrations off the
California coast and elsewhere are likely to be substantially lower.
Figure 4b (left): Simulated
time evolution of cesium-137
activity concentrations on the
Pacific Coast of North
America at 49º N and 30º N,
and near the Hawaiian
Islands. Reproduced from
Rossi et al. (2013) (52).
Concentrations are likely
overestimates.

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