Seven years on, since the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident, it is useful to start to bring together information from scientific studies of the impact of the contamination on the North American environment and its people. I recently wrote to communicate the most recent results of the Integrated Fukushima Ocean Radionuclide (InFORM) project. This post summarizes a recently published, peer-reviewed paper by colleagues lead by Dr. Krzyzstof Starosta of Simon Fraser University in BC working in parallel to InFORM. The open access paper was published in the Canadian Journal of Chemistry and was recently recognized with the “Best Paper Award” by the journal. They studied the concentrations of anthropogenic radioisotopes (134Cs half-life ~2 years, 137Cs half-life ~30 years) and naturally occurring radioisotope 40K (half-life 1.25 billion years) in Pacific salmon (sockeye, chum and chinook) and in soil and roof debris collected in southern British Columbia to determine the local impact of the FDNPP accident. Their results were as follows:
- 134Cs (a fingerprint of Fukushima contamination) was not detected in any of the salmon samples
- 137Cs was not detected in sockeye or chum salmon but was detected in all chinook with an average level of ~0.2 Bq kg-1
- annual dose from artificial radionuclides to a human consumer of chinook salmon was estimated to be ~1/300 of the dose owing to naturally occurring isotopes in the fish and ~1/30,000 of the annual dose experienced for all other natural sources by the average Canadian
- Most soil samples contained 134Cs and 137Cs which was delivered to the region by atmospheric transport shortly after the disaster
- Levels of Fukushima radioisotopes in soil did not approach levels known to be harmful to living organisms
Consistent with other monitoring in the area the results of the study indicate that given the trace levels of contamination present the impact of the FDNPP accident on ecosystem and public health in North America will be insignificant.
Measurements of Sockeye, Chum and Chinook (King) Salmon
Domingo et al. (2017) obtained 3 sockeye (Oncorhynchus nerka), 3 chum (O. keta), and three chinook (O. tshawytscha) salmon samples on 16 November 2013 from spawning sites in Harrison River, Kilby Provincial Park, BC. Four Chinook samples were collected near to spawning sites in the Quesnel River near Likely, BC, on 6 October 2014.
Soil and Roof Debris
Two topsoil samples were collected on 21 March 2014 in Queen’s Park, New Westminster, BC and 4 topsoil samples were collected on 12 April 2014 from the forest near the Harrison River in Kilby Provincial Park, BC. An additional soil sample was collected on 12 April 2014 in a neighborhood located in Mission, BC. A roof-debris sample which was mostly pine needles plant debris was collected on 5 June 2014 from a house in Vancouver, BC. Sampling locations for salmon and soil are shown on the figure below.
Location where salmon samples and soil samples were obtained for the study. Black stars indicate soil or roof-debris sampling locations while grey squares indicate where Pacific salmon samples were obtained.
Results of Radionuclide Analysis (Gamma Spectrometry)
Results comparing the levels of human-made radioisotopes (134Cs and 137Cs) to naturally occurring isotopes (40K, 7Be which tracks mostly rainfall and atmospheric deposition, and 210Po which was alpha counted by Health Canada on other fish samples) are presented for the salmon and soil samples in the tables below:
In the case of the salmon, artificial radionuclides were not detected in sockeye and chum salmon collected in 2013 and 2014. Neither was the Fukushima tracer 134Cs detected in any of the salmon species sampled. What this means is that human-made isotopes from Fukushima could not be detected, even with our most sensitive equipment, in these predatory fish in 2013-2014. 137Cs was detected at very low levels in chinook salmon but these levels (0.16 to 0.36 Bq kg-1) were not significantly different from levels detected in fish before the FDNPP accident in 2011. Calculations of the ionizing radiation dose experienced owing to the consumption of these fish from human-made radioisotopes was a fraction of the dose due to naturally occurring isotopes of potassium and polonium. Relative to the average annual dose experience from all sources (air, water, food etc. which is 1,800 µSv/year) the dose from artificial isotopes is insignificant. Neither the doses from human-made nor natural isotopes in fish would remotely approach doses known to cause significant or measurable impacts on the health of the fish or human consumers. Comparison of the ionizing radiation doses are given the table below.
Soil results showed that 137Cs and 134Cs were present in most samples. In soil samples with 134Cs the knowledge that both radioisotopes were released in roughly a 1:1 ratio from Fukushima allowed an estimate of how much 137Cs was present specifically from Fukushima relative to previous sources (weapons testing and Chernobyl). About 2-17% of 137Cs in soils in the Vancouver area was attributable to Fukushima with the majority still present from 20th century sources. Fukushima is not a dominant signature in soils in this part of Canada. Roof debris more strongly affected by Fukushima atmospheric fallout with about 70% of the radiocesium from the more recent 2011 event. Given the young age of roof materials relative to soils this might be expected. In each case, soil and roof debris, the activity of the human-made isotopes were lower than naturally occurring isotopes and well below action levels for food and water in Canada and therefore not a significant health risk for Canadians.
Activity of radiocesium in soil and roof debris collected near to Vancouver British Columbia Canada in 2014 three full years post Fukushima.
Summary
Pacific salmon investigated in this study were not found to contain radiocesium (sockeye and chum) or when 137Cs was present (chinook) 134Cs from Fukushima was not detectable. This suggests that Fukushima had little impact on the levels of human-made isotopes in salmon in the northeast Pacific Ocean. Ionizing radiation dose from fish consumption is still dominated by naturally occurring isotopes always present in the fish and these doses to not represent a health risk to the fish or to people who eat them. Investigation of radioisotopes in soil and roof debris indicate too that the delivery of isotopes from Fukushima came largely from the atmosphere in the weeks to month following the disaster with other legacy sources (weapons testing and Chernobyl fallout) contributing the majority of the isotope levels measured. Fukushima’s fingerprint was stronger in roof debris but levels in soils and roof material were far below levels of concern and would not represent a health risk. Overall, the measurements presented by Domingo et al. (2017) reinforce the studies of other groups here that demonstrate that the FDNPP accident is a low risk event with respect to the health of North America’s ecosystems and public. There are unlikely to be measurable impacts on the health of North Americans and the risk to them from the event is insignificant.
