Radioactivity concentration measurements in fish and shellfish samples from the west coast of Canada after the Fukushima nuclear accident (2011-2018).

Radioactive contamination of the Pacific Ocean following the Fukushima nuclear accident has raised public concern about seafood safety, particularly in coastal Indigenous communities. To address this, Health Canada and partners have collected and analyzed a total of 621 samples of commonly consumed salmon, ground fish, and shellfish from the Canadian west coast from 2011 to 2018. While the vast majority of the 137Cs and 134Cs levels were below the Minimum Detectable Concentration (MDC, typically 0.7-1.0 Bq kg-1 fw for a 6 h counting), further examination of 19 fish samples revealed 137Cs concentrations of 0.17-0.53 Bq kg-1 fw with an average value and uncertainty (k = 1) of 0.29 ± 0.02 Bq kg-1 fw. Of these, only two samples were found to have trace levels of 134Cs likely derived from the Fukushima accident. The global fallout contribution from atmospheric nuclear weapons testing to the observed 137Cs in these two samples was determined to be 0.26 ± 0.08 Bq kg-1 fw (49 ± 14%) and 0.12 ± 0.02 Bq kg-1 fw (24 ± 4%) for collection years 2015 and 2016, respectively. The annual average level of 137Cs in fish and shellfish was also determined by spectral summation for collection years 2014-2018. In fish, 137Cs levels determined through spectral summation were relatively constant (0.18-0.25 Bq kg-1 fw) with an average value and uncertainty of 0.21 ± 0.02 Bq kg-1 fw. By contrast, 38 shellfish samples (bivalves) were measured and revealed no radiocesium or other anomalies in either tissue or shell. In all, measurements over eight years showed that the radioactivity in fish and shellfish was dominated by natural radionuclides and that the level of anthropogenic radionuclides, as indicated by the radioactive cesium content, remained small. An upper bound for ingested dose from 137Cs was determined to be approximately 0.26 µSv per year, far below the worldwide average annual effective dose of 2400 µSv from exposure to natural background radiation. We can therefore conclude that fish, such as salmon, ground fish, and shellfish from the Canadian west coast are of no radiological health concern despite the Fukushima Dai-ichi nuclear accident of 2011.

Relationship between surface dissolved iron inventories and net community production during a marine heatwave in the subarctic northeast Pacific.

From winter 2013-14 to the end of 2015-16, a high pressure atmospheric system induced elevated sea surface temperatures in the offshore subarctic northeast Pacific, resulting in a marine heatwave. Increased stratification due to the heatwave resulted in shoaling of the winter mixed layer and a decrease in nutrient re-supply to the euphotic zone. Here, we investigate relationships between dissolved iron (dFe) and macronutrients, net community production (NCP), (micro)nutrient uptake ratios, and phytoplankton community composition in the winter and summer from 2012 to 2015 to gain insight into coupled biogeochemical responses to the heatwave. Our investigation highlights the importance of external dFe supply during marine heatwave events, as a more shallow mixed layer reduces the transport of essential (micro)macronutrients to the surface layer. We conclude that recycled dFe did not contribute to NCP in 2014, but rather the vertical displacement of dFe rich water unrelated to mixed layer deepening played a major role. In 2015, such transport was not detected, resulting in abnormally low dFe and shift toward higher biomass of pico- and nano-phytoplankton size-classes.

210Po in Pacific Salmon from the West Coast of Canada and its Contribution to Dose by Ingestion.

In response to public concern in Canada regarding health impacts attributable to the Fukushima Daiichi nuclear accident, oceanic seawater samples from the north Pacific and Arctic oceans, coastal seawater samples from 16 locations along the British Columbia coastline, and seafood samples (salmon, steelhead trout, and shellfish) from British Columbia coastal waters were collected and analyzed. This paper reports radiological analysis results of Pacific salmon samples (Oncorhynchus species) obtained from summer 2013 to fall 2016. While radioactive cesium from the Fukushima disaster was not detectable in most salmon samples, naturally occurring Po was measured in almost all individual samples in varying activity concentrations, from below the detection limit of 0.2 Bq kg fresh weight up to 4.7 Bq kg fresh weight. The average Po concentration among 297 salmon samples was 0.73 Bq kg fresh weight. The average ingested radiation dose per kilogram of salmon from Po is estimated to be 0.88 µSv, and the average dose from Cs is estimated to be 0.0026 µSv. The annual dose from ingested salmon would be only a fraction of the worldwide average annual effective dose from exposure to natural background radiation (2,400 µSv y) (). The measurement results showed clearly that radiation doses to people consuming fish (such as salmon) from the Canadian west coast pose no health concern.

A disposable sticky electrode for the detection of commercial silver NPs in seawater.

The ability to perform efficient and affordable field detection and quantification of nanoparticles in aquatic environmental systems remains a significant technical challenge. Recently we reported a proof of concept of using 'sticky' electrodes for the detection of silver nanoparticles (Tschulik et al 2013 Nanotechnology 29 295502). Now a disposable electrode for detection and quantification of commercial Ag nanoparticles in natural seawater is presented. A disposable screen printed electrode is modified with cysteine and characterized by sticking and stripping experiments, with silver nanoparticle immobilization on the electrode surface and subsequent oxidative stripping, yielding a quantitative determination of the amount of Ag nanoparticles adhering to the electrode surface. The modified electrode was applied to natural seawater to mimic field-based environmental monitoring of Ag NPs present in seawater. The results demonstrated that commercial Ag NPs in natural seawater can be immobilized, enriched and quantified within short time period using the disposable electrodes without any need for elaborate experiments.

Electrochemical detection of commercial silver nanoparticles: identification, sizing and detection in environmental media.

The electrochemistry of silver nanoparticles contained in a consumer product has been studied. The redox properties of silver particles in a commercially available disinfectant cleaning spray were investigated via cyclic voltammetry before particle-impact voltammetry was used to detect single particles in both a typical aqueous electrolyte and authentic seawater media. We show that particle-impact voltammetry is a promising method for the detection of nanoparticles that have leached into the environment from consumer products, which is an important development for the determination of risks associated with the incorporation of nanotechnology into everyday products.

Direct electrochemical detection and sizing of silver nanoparticles in seawater media.

We report proof-of-concept measurements relating to the impact of nanoparticles with an electrode potentiostatted at a value corresponding to the diffusion controlled oxidation of silver nanoparticles in authentic seawater media. The charge associated with the oxidation reveals the number of atoms in the nanoparticle and thus its size and state of aggregation.