Radiation after Fukushima

The nuclear accident at the Fukushima Daiichi reactor plant caused by the Tōhoku earthquake (9.0 magnitude) and tsunami on the eastern coast of Japan on March 11, 2011 was considered a looming threat for the Pacific Ocean in terms of human health and marine biodiversity. Following the nuclear aftermath, researchers from major universities in B.C. and across Canada, as well as the Government of Canada, started monitoring along the B.C. coast. To assess the level of radiation released from Fukushima, three major tracers or isotopes – known as cesium 134 (¹³⁴Cs), cesium 137 (¹³⁷Cs), and iodine (¹³¹I) – were measured in seawater, seafood, and fish samples. This was an important step because the potential contamination of seafood through bioaccumulation of radioisotopes in marine and coastal food webs was a major public health concern for coastal communities – particularly the bioaccumulative ¹³⁷Cs isotope.

Understanding radiation or radioactivity released from nuclear accidents is important because of the potential human health effects, such as thyroid gland cancer, leukemia, genetic disorders, and other diseases. Direct exposure to radiation or consumption of contaminated food (i.e., above safe limits or thresholds identified by government to protect public health) is a risk to human health. For instance, radioactive iodine (¹³¹I) can affect the thyroid gland immediately and fatally if levels are higher than a given “action level” (i.e., safe limit or threshold) recommended in guidelines.

While the concentrations of ¹³⁷Cs in marine fish and other seafood in the B.C. marine environment have been reported to be low since the Fukushima accident, the trends of radioactive ¹³⁴Cs and ¹³⁷Cs activities in organisms have differed greatly among taxonomic groups, habitats, and spatial distributions. Contamination through trophic transfer of radioactive isotopes through food webs is likely to affect long-lived predators feeding at the top of the food web, including fish-eating seabirds and marine mammals inhabiting offshore and coastal habitats of the region. Simulations that model the biological accumulation of ¹³⁷Cs in Chinook salmon (Oncorhynchus tshawytscha) and fish-eating southern resident killer whales (Orcinus orcas) from B.C. predicted trophic magnification of ¹³⁷Cs via the food web in these species (Figure 1). The potential confounding impacts of higher ocean surface temperatures or of ocean acidification on radioisotopes in food webs are unknown.

Figure 1. Environmental transport (atmospheric and oceanic) and pathways of exposure and accumulation of the radioisotope ¹³⁷Cs in the food web of fish-eating (resident) killer whales. Adapted from Alava and Gobas (2016).

Although radioactivity levels in fish products are not considered to pose a risk to people at the present time, concerns remain about the long-term exposure and bioaccumulation of radioactivity in marine food webs of the North Pacific. Particularly vulnerable are First Nations peoples who are intimately connected with the oceans and rely strongly on the harvest and consumption of traditional seafood and fish products (e.g., Pacific salmon).

Understanding pollution risks is critical, as healthy ocean food webs are key to the socioeconomic viability of coastal B.C. communities in terms of spiritual ecology, culture, and human connections. Seafood consumption by coastal First Nation communities in B.C. is 15 times higher than the average Canadian consumer, and 64 percent of consumed seafood is salmon, thus indigenous people could be exposed to much more radioactivity (e.g., ¹³⁷Cs) than non-indigenous people in the long-term.

Following the upriver migration and spawning in breeding grounds, samples of Pacific salmon were collected from the Harrison River (Kilby Provincial Park, B.C.) in 2013 to measure radioisotopes (e.g., ¹³⁷Cs). Some species of Pacific salmon (e.g., Chinook and sockeye) can be used as sentinel species, because of their role as biovectors of pollution, to track anthropogenic radioisotopes such as ¹³⁴Cs and ¹³⁷Cs in the Northeastern Pacific. (Photo: Citizen scientist, Aki Sano)

While uncertainties linger concerning the cancer risk assessment at low doses of radiation to humans, the Fukushima-derived doses received from fish consumption (e.g., tuna fish) by subsistence fishers were estimated to be two additional fatal cancer cases per ten million similarly exposed people. Based on a study of Fukushima-derived radioactivity in sockeye salmon (Oncorhynchus nerka) from West Vancouver Island, traditional seafood is still quite safe for human consumption.

The arrival of seawater carrying one of the radioisotopes (¹³⁷Cs) associated with the Fukushima accident was detected in offshore waters west of Vancouver Island (1,500 kilometres west of B.C.) at depths of 0–100 metres starting in 2012. The measured concentrations of ¹³⁷Cs were extremely low in 2012 and increased by 2016 (Figure 2). According to the data posted by the Integrated Fukushima Ocean Radionuclide Monitoring or Fukushima InFORM network, levels in January and February 2017 were still well below the recommended Canadian Action Levels for Radionuclides in Drinking Water of 100 Bq/L.

Figure 2. Concentrations of Fukushima-associated ¹³⁷Cs measured in oceanic waters off the west coast of Vancouver Island from 2011 to 2016, and coastal seawater in British Columbia in 2017. There was no detection of Fukushima-associated ¹³⁷Cs in 2011. The red dashed line represents the Canadian Action Level for ¹³⁷Cs in water as recommended by the Canadian Guidelines for the Restriction of Radioactively Contaminated Water Following a Nuclear Emergency. Data from Smith et al. (2015), Smith et al. (2017) and Fukushima InFORM.

Other research shows that levels of ¹³⁷Cs in several species of Pacific salmon are either below detection levels or well below the recommended action level (Figure 3). Due to their four to five year lifecycle, Pacific salmon returning to B.C. streams in more recent years will have spent longer feeding in the radiation-contaminated marine environment than those that returned, for example, in 2011, the year of the Tōhoku earthquake. Overall, these findings will further contribute to the understanding of the fate of radioactive contamination from Fukushima in ecosystems in B.C.

Figure 3. Mean concentrations (Bq/kg fresh weight) of ¹³⁷Cs measured in Pacific salmon species from two rivers (Harrison and Quesnel) and Alberni Inlet, on the west coast of Vancouver Island. Chinook salmon samples collected from the Harrison River in 2013 and Quesnel River in 2014, and half of sockeye salmon samples collected from the Alberni Inlet revealed detectable concentration for ¹³⁷Cs. Error bars are standard deviations calculated from the number of sockeye and Chinook salmon samples analyzed. Data from Domingo et al (2016, 2017).

Projections using food web modelling indicate that the ¹³⁷Cs levels in Pacific herring, sablefish, halibut, Pacific salmon (pink, chum, and Chinook), and killer whales will remain far below the Canada Action Level for food consumption (i.e., 1000 Bq/kg). In this context, while no radiation risks are expected thus far to the general public and coastal communities from the consumption of Pacific salmon and other fish products harvested from marine coastal waters off B.C., environmental radiation is still not well understood. Thus an understanding of the basic nature of radiation’s adverse effects on human bodies and other organisms (i.e., internal exposure dose in the human body versus external exposure dose found in contaminated food, water, and soil), as well as the mechanisms for how radiation affects the chemical world is strongly warranted.

Individual and Organization Actions:

• Get involved as citizen scientists and continue to support regional efforts to monitor Fukushima radiation on our B.C. coast (contact the Fukushima InFORM network).
• Get involved as citizen scientists to collect samples in other less studied areas.
• Inform yourself on levels of radiation that are considered dangerous and harmful.

Government Actions and Policy:
 

• Reach out to citizens with regular information on radiation levels and risks related to seafood consumption.