Measurements undertaken as part of the InFORM project to look for Fukushima derived radionuclides in fish during our second of three years of monitoring are now complete on an additional 156 fish. Sockeye salmon (Oncorhynchus nerka) and Steelhead Trout (Oncorhynchus mykiss) (as well as some Chinook (Oncorhynchus tshawytscha) and Pink (Oncorhynchus gorbuscha) Salmon) were caught off the west coast of Canada in Summer 2015 as they were returning to their home streams and rivers up and down the coast of British Columbia. Samples of fish were obtained with the cooperation and collaboration of the Champagne and Aishihik, ‘Namgis, Nisga’a, Selkirk, Syilix, Tahltan, Taku River Tlingit, Tr’ondëk Hwëch’in, Wet’suwet’en and Wuikinuxv First Nations. These results add to the first ~100 fish collected and analyzed in 2014.
What we have found so far:
- With the exception of 7 fish discussed in point 3 below individual fish were not found to have detectable levels of either 134Cs or 137Cs so average levels were calculated for all fish harvested in a given location.
- Similar to 2014, none of the fish from 2015 analyzed thus far were found to contain detectable levels of 134Cs a man-made radionuclide that serves as a fingerprint of the Fukushima disaster.
- The average level of 137Cs seen in InFORM 2015 fish samples (0.19 Bq kg-1) is similar to the level observed in the 2014 campaign (0.21 Bq kg-1). As with 134Cs, the Fukushima disaster resulted in the release of a large quantity of 137Cs. However, 137Cs, which has a longer half-life, was already present in the Pacific Ocean prior to the Fukushima accident because of the nuclear weapons testing fallout.
- The 137Cs levels observed in the 2015 InFORM samples represent a fraction of the Health Canada guidelines (1000 Bq kg-1) and a fraction of the radiation exposure owing to naturally occurring radionuclides Polonium-210 (210Po) and Potassium-40 (40K) which dominate the ionizing radiation dose to fish consumers.
- While the average 137Cs concentration remained nearly identical from 2014 to 2015, 7 individual fish (out of 156) have shown a detectable level of 137Cs (ranging from 0.27 to 0.60 Bq kg-1) while individual fish from 2014 were below detection limit. Because no 134Cs was detected in these fish it is not possible to say whether detectable 137Cs can be attributed to Fukushima contamination or simply normal variability in contamination owing to nuclear weapons testing fallout.
- What this means is that radioactivity from the Fukushima meltdowns has not been detected in the InFORM fish samples caught in BC waters as of summer 2015.
- Neither the 137Cs present in the fish nor the naturally occurring radioisotopes in fish represent a measurable health risk to consumers in Canada.
Measurements of radioactive elements in these fish and from previous years are available for download at the Government of Canada Open Data website.
What are we measuring and why?
The triple meltdowns at the Fukushima Dai-ichi nuclear power plant (NPP) released many different radioisotopes to the environment, however only a very few of these are both measurable and unique to Fukushima. A reliable finger-print radioisotope for Fukushima is Cesium-134 (134Cs half life ~ 2 years). This is because 134Cs is only produced appreciably in nuclear reactors and it has a relatively short half-life, so that 134Cs from other human sources, like the Chernobyl NPP disaster in 1986, are no longer present in the environment. Other isotopes such as Cesium-137 (137Cs half life ~30 years) are not positive indicators of Fukushima since they were also a products of atmospheric weapons testing in the 20th century and Chernobyl and are still present in the environment from these legacy sources.
How scientists talk about radioactivity in the environment
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). The measurements above represent that numbers of Bq detected in a kilogram (wet weight) of fish flesh.
Measurements of Pacific Fish
We focused on measuring the activities of cesium radioisotopes 134Cs and 137Cs that were released in large quantities from the Fukushima Dai-ichi Nuclear Power Plant disaster in 2011. We also measured naturally occurring radioisotopes Potassium-40 (40K) and Polonium-210 (210Po) (results pending) that always contribute doses of ionizing radiation to human consumers of marine fish. By adding together the signals obtained for all the fish collected from a given sampling location we can calculate and detect an average activity concentration of 137Cs. This represents residual 137Cs in the North Pacific largely from atmospheric nuclear weapons testing in the last century. At present, Fukushima derived radionuclides cannot be detected in any of the fish we have collected as of 2015. Nuclear weapons testing fallout (137Cs) can be detected in BC fish at levels that represent a fraction of the radiation exposure owing to naturally occurring radionuclides. Neither the exposure to artificial or natural radionuclides represent a dangerous health risk to consumers in Canada. We plan to collect more pacific salmon in 2016 to continue to monitor for Fukushima contamination and report results as they are generated here.
The Importance of Salmon to Canadians
Pacific salmon are economically, culturally, and ecological significant species to British Columbia. On an annual basis, the commercial, recreational, and First Nation salmon fisheries contribute over $600 million in revenues. They are an important food source to First Nations and coastal communities, and numerous animal species such as endangered Killer Whales, Gray Wolf, Grizzly Bear, seabirds, and insects. They provide nutrients to freshwater ecosystems and riparian habitats through the decomposition of their carcass.
There are six species of Pacific salmon in British Columbia. Initially, InFORM will focus on Sockeye Salmon (Oncorhynchus nerka) and Steelhead Trout (Oncorhynchus mykiss), though other salmon species have and will be examined. Both species typically spend 2-3 years in the North Pacific Ocean prior to returning to their natal streams and venture further west than any other salmon species (see figures below). On an annual basis, 1-10 million Sockeye Salmon are commercially harvested for human consumption and ceremonial purposes. In contrast, the fishery for Steelhead Trout is primarily catch and release due to conservation concerns for this species, particularly in Southern British Columbia. Although wild Steelhead Trout are not frequently consumed in Canada, their extensive westward migration that brings them close to the coast of Japan makes them an ideal canary species for monitoring radiation levels in salmon species originating from British Columbia.
Technical Information Regarding Sample Analyses
- 156 fish samples, flesh only were obtained through the cooperation of Fisheries and Oceans Canada and the Champagne and Aishihik, ‘Namgis, Nisga’a, Selkirk, Syilix, Tahltan, Taku River Tlingit, Tr’ondëk Hwëch’in, Wet’suwet’en and Wuikinuxv First Nations
- A sub-sample of ~125 g of wet mass was taken and placed in a sample counting container
- Gamma-radiation emitting isotopes were measured by gamma spectroscopy using a high purity germanium detector and each sample being counted for 6 hours
- Planar BE5030 high purity germanium (HPGe) detector with relative counting efficiency of 46%
- counting geometry = Parkway Jar (Polyethylene, active volume = 129 mL) placed in a polyacrylate sample holder (2.95 mm thickness)
- counting efficiency was determined by applying an empirical efficiency curve, determined from a multi-nuclide (12) standard (Eckert and Ziegler Analytics, SRS: 79535-411) of similar density (1.15 g cm-3, Parkway Jar format) spanning energies of 46.5 – 1836.1 KeV
- true coincidence summing (where applicable) is accomplished by extracting detailed decay scheme data from the UniSampo-Shaman nuclide library
- Spectral summation was done by adding all the spectrum into a single one and then reanalysed using UniSampo-Shaman gamma spectral analysis software from Baryon Oy, Ltd., Finland, with decay correction to the catch date. A typical summation of 10 samples results in a detection limit for 134Cs of 0.2 Bq kg-1