Data from July and August samples keep creeping up the steady trend of increasing 137Cs concentations which indicates the Fukushima plume is in BC coastal waters. Interestingly, while the overall trend is for increasing 137Cs concentrations along the coast, the past few samples from Vancouver have measured near the lowest concentrations of our entire record. These low concentrations may be a temporary blip in an otherwise slight increasing trend, but time will tell that tale.
A possible reason for such low readings could be that a particluarly fresh parcel of water was sampled. While we await the salinity analysis for those Vancouver samples, we would generally expect that fresh river water would have low concentrations of 137Cs since much of the atmospherically deposited 137Cs (from weapons testing and Fukushima) that was mobile has already been transported through the watershed to the sea. If the samples from Vancouver are shown to have low salinity, the samples were likely collected in the freshwater ‘lens’ from the Fraser River. May through July are the months with the greatest runoff from the Fraser watershed as warmer temperatures melt the snowpack. We predict that coming results will show a return to levels seen earlier in the spring.
Vancouver regularly has the lowest activities of 137Cs in its samples. This is likely due to two factors. The first is that it is within the Salish Sea, landward of the intense mixing action that occurs as ocean waters mix with fresh estuarine waters through the US San Juans and Canadian Gulf Islands. This mixing dilutes whatever signal may be present and it is thought that only ~40% of water incoming to the Strait of Georgia is new water from the Pacific, with the majority being composed of recirculated surface waters. We know that the deep waters of the Straight of Georgia are “renewed” with dense, oxygen-rich, Pacific water each year between July and September and that it takes ~5-6+ months for this denser water to be brought to the surface of the Sea. Second, as mentioned above, the fresh river waters from the Fraser also have a low activity signal. Therefore, with these two factors, it is possible that the waters near Vancouver may never have a significant increase in the 137Cs signal.
The blip of low activity water from Vancouver would not be the first such blip in our monitoring record. As we see in the regional averages, the observations are showing that the plume is quite dynamic, still with numerous regions of higher and lower concentrations even after the 10,000 km journey from Japan. Mixing and decay of the plume signal will continue over the coming years as circulation continues, just as creamer eventually becomes well mixed, or homogeneous, thorughout your coffee cup.
For the first time, the Fukushima fingerprint isotope, cesium-134 (134Cs), has been found in Canadian salmon. The sockeye that tested positive was sampled from Okanagan 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 new measurement used the same samples that were analyzed and reported on last winter. However, to test a hypothesis that extremely low levels of 134Cs may be present, the scientists re-examined some of the samples more closely. The results of this effort were that trace (0.07 Bq kg-1) levels of 134Cs were detected in the one sample from Okanagan/Columbia River population confirming their theory. The observed levels remain well below the action level according to Health Canada guidelines. Read the full results ->
Results from InFORM’s 2016 biotic monitoring results are now available and reveal that Fukushima contamination was not detected in sampled BC salmon after initial testing. These results are an update to the earlier report on the first 20 of the 123 fish donated by First Nations from 10 rivers in British Columbia and Yukon in 2016. Nine fish did have individual levels of 137Cs detected near the minimum detectable concentration (MDC). These levels (<0.7 Bq kg-1) are not known to present a significant health risk and are ~1,400x lower than the national and international action level (1000 Bq kg-1). For perspective, you would need to consume 1000-1500 kg of salmon at this concentration of cesium to receive the same radiation dose acquired during a single cross country flight. There has not been a significant increase to the total 137Cs concentration in BC salmon since InFORM monitoring began in 2014. . Read the full results ->