For the first time, the Fukushima fingerprint isotope, cesium-134 (134Cs; half-life ~ 2 years), has been detected at an extremely low level in a Canadian salmon by the InFORM project. The single sockeye salmon that tested positive was sampled from Osoyoos Lake in the summer of 2015, according to scientists from the Radiation Protection Bureau at Health Canada, in cooperation with Fisheries and Oceans Canada and local First Nations. The sample was one of a few (8 out of 156 total) individual fish that had trace levels of the longer lived cesium-137 (137Cs) (30 yr half-life) that we reported on last winter. To determine if this trace 137Cs was from Fukushima or remnant from atmospheric weapons testing, InFORM reexamined these individual fish samples to see if extremely low levels of 134Cs may be present. The results of this extended analysis show that trace (0.07 Bq kg-1) levels of 134Cs were detected in one sample from Okanagan/Columbia River population. No 134Cs was detectable in the other samples. The observed levels remain well below the action level (1000 Bq kg-1) set by Health Canada guidelines. Continue reading Pushing the Limit: Fukushima Fingerprint Isotope Found in Salmon from 2015→
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 individualfish (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.