This short blog summarizes an open access paper published today reporting results from a Canadian monitoring program tasked with documenting the arrival of ocean borne Fukushima contamination along the North American Pacific coast. This diary is part of an ongoing effort to communicate the best science available on the impacts of the Fukushima Dai-ichi meltdowns on the environment. High quality measurements to look for Fukushima derived radiocesium were made in seawater in the North Pacific and Arctic Oceans from 2011 to early 2014. The authors concluded that:
Fukushima derived radiocesium was first detected 1500 km west of British Columbia Canada in June 2012
Contamination was detected on the continental shelf (near coastal waters) in June 2013
By February 2014 Fukushima radiocesium was present at levels similar to preexisting weapons testing derived 137-Cs
These same models predict that total radiocesium levels from weapons testing fallout and Fukushima will likely reach maximum values of ~3-5 Becquerel per cubic meter (Bq m-3 of seawater in 2015-2016 and then decline to fallout background level of ~1 Bq m-3 by 2021
Fukushima will increase northeastern Pacific water to levels last seen in the 1980’s but does not represent a threat to environmental or human health
This diary summarizes a newly published paper by Hewson and colleagues in Proceedings of the National Academy of Sciences of the USA which investigated the cause of sea star die offs along the west coast of North America. This diary is part of series dedicated to summarizing scientific research on the impact of the triple meltdowns at the Fukushima Dai-ichii nuclear power plant on the North Pacific Ocean and the health of residents of North America. Northeast Pacific sea stars have experienced a mass die off recently and have disappeared from certain coastal ecosystems as a result. The Hewson et al. paper presents evidence that the cause of the wasting disease can be transmitted between affected to healthy individuals. The disease-carrying agent is virus sized and likely sea star-associated densovirus (SSaDV) which is found in greater numbers in diseased versus healthy sea stars. They also detected SSaDV in museum specimens of sea star dating from 1942 indicating that the virus has had a long term presence along the North American west coast.
Hewson and colleagues examined affected and asymptomatic sea stars to demonstrate that an infective agent was responsible for SSWD. To do this they took homogenized SSWD affected sea stars and administered an inoculate or a heat killed inoculate of virus size containing filtrate to tanks containing healthy individuals. Results of these experiments indicate that heat killed inoculates did not lead healthy individuals to develop SSWD while inoculates with potentially live viral particles lead to SSWD symptoms in the previously healthy population. Previously healthy sea stars had very low loads of a virus callled Sea Star-Associated Densovirus (SSaDV) while after developing symptoms much higher amounts of SSaDV were found in the sea stars.
The authors then looked for the virus in asymptomatic and SSWD affected individuals in the wild finding that affected individuals were about 3 times more likely to be virus carrying than asymptomatic individuals. The virus was also found in plankton, sediments and other echinoderms. The presence of the virus in plankton and in filtration media of public aquaria affected by SSWD is consistent with observations that the disease could spread through ocean currents between infected and uninfected areas of the coast.
The authors conclude by pointing out that the spread of SSWD along our coast is most consistent with an infectious agent. Based on their observations and laboratory experiments this agent is most likely SSaDV which has been present along the coast for at least 72 years. Fukushima in not mentioned once in the article as there is no scientific evidence to relate SSWD to the trace concentrations of Fukushima derived radionuclides present offshore.
The authors identify outstanding questions as follows:
How exactly (by what mechanism) does SSaDV kill sea stars?
Are there other microbial agents involved in the wasting/death process?
What triggers outbreaks of SSWD?
How will the absence of important predators like sea stars affect the marine ecosystem along our coast?
The study highlights the increasingly recognized importance of marine viruses in helping to shape community structure and ecosystem dynamics in the ocean.
The purpose of this post is to report measurements of radioactivity in fish caught off the west coast of Canada based on the work of InFORM team member Dr. Jing Chen. A collaborative effort between Health Canada, Department of Fisheries and Oceans Canada, and the University of Victoria was published in May 2014 in the peer-reviewed, open-access scientific journal Radiation Protection Dosimetry (link). The authors examined the activities of cesium radioisotopes (134-Cs half-life ~2 years and 137-Cs half-life ~30 years) that were released in large quantities due to the triple reactor meltdowns at Fukushima Dai-ichi Nuclear Power Plant in 2011 as well as a naturally occurring polonium isotope (210-Po) that can pose radiological health concerns for human consumers of marine fish. Samples of chum and coho salmon, halibut, sablefish and spiny dogfish were analyzed and none were found to contain detectable levels of Fukushima derived radionuclides. Radiation doses to human consumers were determined by assuming a conservative worst case scenario where Cs isotopes were present at detection limits of the measurement and found to be 18 times lower than doses attributable to the naturally occurring, alpha-emitter 210-Po. The authors conclude that the radiation dose from Fukushima derived isotopes present in fish caught in Canadian waters represent a very small fraction of the annual dose from exposure to natural background radiation. Based on these measurements, at present, Fukushima derived radionuclides in fish do not represent a significant radiological health risk to Canadians. Continue reading Looking For Fukushima Radionuclides in Fish Caught Off the West Coast of Canada→
The purpose of this post is to summarize results from various studies that monitored the timing of arrival and activity of radioactive iodine falling from the atmosphere in western North America following the Fukushima disaster in 2011. Determining the activity of 131-I (half life ~8 day) in rain and seaweed, which serves as a biological monitor, is important because of the isotopes short half life and its propensity to concentrate in the human body, specifically the thyroid gland. This combination of rapid energy release and biological tissue targeting can represent a potential radiological health risk. Measurements of 131-I in rain collected in the San Francisco Bay area and southern British Columbia, Canada indicate that the atmospheric transport brought contaminated air from Fukushima to North America by March 18 roughly 1 week after the earthquake and tsunami. Depending on location, activities of 131-I in rain peaked between March 20-24 and were observed to decrease to background levels in the first week of April. Peak activities in seaweed occurred later on March 28 and were observed to return to background levels in mid-May. Maximum 131-I activities in rain resulting from Fukushima were a factor of 10 lower for rainwater and a factor of 40-80 lower for seaweed compared to similar measurements made following the Chernobyl disaster in 1986. Observed 131-I activities suggest that the upper limit of radiation dose to the public resulting from Fukushima was similarly an order of magnitude lower than that from Chernobyl suggesting that the short and long-term impact on human health in western North America is expected to be minor.
How Scientists Talk About Radioactivity
Scientists use a variety of units to measure radioactivity. A commonly used unit is the Becquerel (Bq for short) which represents an amount of radioactive material where one atom decays per second and has units of inverse time (per second). Another unit commonly used is disintegrations per minute (dpm) where the number of atoms undergoing radioactive decay in one minute are counted (so 1 Bq = 60 dpm).
131-Iodine Releases From Fukushima
As a result of the great eastern Japan earthquake and tsunami on March 11, 2011 three of six reactors melted down resulting in releases of radionuclides from the Fukushima Dai-ichi nuclear power plant to the environment. In terms of absolute activity released and potential for causing harm to organisms, 131-I (half life ~8 day) was one of the most significant. Given its volatility and the damage to reactor fuel rods large releases of ~2000 PBq (petaBequerel = 10^15 Bq) to the atmosphere and ocean occurred in the weeks following the disaster. Prevailing atmospheric circulation brought this plume of contaminated air to North America within one half life of 131-I where rain and fallout of aerosol particles delivered 131-I and other isotopes to land and coastal waters.
Monitoring of 131-I in the environment is important because as an essential nutrient when concentrated in the human body in the thyroid gland the decay of the isotope can cause damage resulting in negative health impacts like cancer. After the triple meltdowns stations in North America began monitoring the activities of released radionuclides in air, rainwater and seaweed to determine the risk to public health.
Rainwater activities of 131-I
Rainwater in the San Francisco Bay area was monitored and the results published in the open-access, peer reviewed journal PLOSOne in 2011 by Norman and co-workers. Measurements were made for the period March 16-26, 2011 on rainwater collected in Oakland, Berkeley hills and Albany, CA. Results of these measurements are summarized in the figure below:
This first sample with Fukushima radionuclides above background concentrations was collected on March 18 and activities peaked at 16 Bq/L rainwater on March 24.
131-I levels in seaweed are known to correlate strongly with levels in rain and seaweeds are useful monitors for human made radionuclides in the environment as the concentrate isotopes from their surroundings and are geographically widespread. Seaweeds were collected along the Canadian west coast by Chester and colleagues and analyzed for 131-I following the Fukushima disaster. Results of these analyses are summarized in the figure below:
Maximum 131-I was detected in BC seaweed on March 22 near Vancouver and on March 28 off the west coast of Vancouver Island some 250 km to the west of the city. Peak activities were 130 and 67 Bq/kg respectively. By mid-May activities had returned to background activities in the seaweed.
Summary: Health Implications and Comparison to Chernobyl
The maximum levels of 131-I in rainwater can be compared to limits allowed in drinking water in both the USA and Canada. Maximum activities in rain were in the range ~6-16 Bq/L. For example the maximum allowable concentration (MAC) or activity allowed in Canadian drinking water is 6 Bq/L. The MAC for 131-I is calculated using a reference dose level of 0.1 mSv (where mSv = 0.001 Sv) for 1 year’s consumption of drinking water, assuming a consumption of 2 L/day at the MAC. This compares to an effective dose received by someone living in Vancouver of about 1.3 mSv. Given the short half-life of 131-I of ~8 days the actual dose attributable to Fukushima fallout in precipitation is likely to be much lower than the 0.1 mSv upper limit on which the drinking water MAC is based.
Indeed, comparing measurements in the studies above to measurements made on the west coast of North America in the aftermath of the Chernobyl disaster in 1986 suggests that doses experienced by the public post Fukushima fallout were an order of magnitude lower. Measurements in the same species of seaweed in 1986 (behind paywall) are compared to the measurements of Chester and others here:
The calculated dose estimates to Canadians following the Chernobyl disaster were on the order of ~1 micoSievert (0.000001 Sv) (What is a Sievert, Sv?) while the peak 131-I activities present in rainwater after Fukushima suggest an upper dose of 0.1 microSv which is an order of magnitude lower dose.
These data have led health professionals in the US and Canada to expect that short-term and longer-term impact of Fukushima on public and environmental health to be very small compared to other radiological impacts from natural and legacy sources of radiation.