Small numbers address some bigger questions

January 2018
RADIOISOTOPES

In the seven years since a tsunami demolished three Fukushima Daiichi reactors in Japan, the radioactive isotopes that spread from this event to Canada’s west coast have dwindled to levels that can only be detected with specialized equipment such as a gamma ray spectrometer. Such hardware can be found in the nuclear science laboratory of Simon Fraser University chemistry Professor Krzysztof Starosta, where he and others are still taking stock of where those isotopes can be found in British Columbia. He acknowledges that they are unlikely to pose any kind of threat to human health, but he is eager to take advantage of what amounts to a unique research opportunity.

Radioisotopes

 Residual radiation from the 2011 Fukushima Daiichi reactor accident poses no threat to human health in Canada but does offer ongoing research opportunities. Photo credit: osaMu

“We don’t want to have accidents like this, but it happened and there’s nothing we can do about it,” Starosta explains. “But we can use it to learn things and that’s what a number of groups have done.”

He and his colleagues published what they learned in the Canadian Journal of Chemistry, where they recounted their findings from a diverse group of samples that included fish collected from two inland river sites along with soil and rooftop debris.  Measurements of two key isotopes linked to Fukushima — cesium-134 and cesium-137 — confirmed their presence in amounts at least an order of magnitude below any regulatory threshold mandated for food and drinking water.

Those numbers should be of some comfort to anyone who may still worry about the possibility that this material would make its way through the natural food chain and reach toxic concentrations in fish that Canadians eat. In fact, radiation from these cesium isotopes is overshadowed by the natural background radiation in the environment.

Starosta acknowledges the limited scope of this volunteer-collected sample analysis, but he points to results that could serve as the basis of further work. For example, no 137Cs was found in salmon, even though there should be some detectable amounts, including from the above-ground nuclear weapons tests of the 1950s and 1960s along with the Chernobyl reactor accident of 1986.

A map showing the spread of radiation after the 2011 Fukushima Daiichi nuclear reactor accident.
A map showing the spread of radiation after the 2011 Fukushima Daiichi nuclear reactor accident. Photo credit: OpenStax

“We really pushed the limit of sensitivity,” he says, noting that this observation drew the attention of oceanographic researchers who value the use of radioisotopes as a method of tracking fish migration.

In the sample taken from a residential roof in the Vancouver area, on the other hand, the laboratory’s detailed analysis revealed a higher concentration of 137Cs from the Fukushima accident, as opposed to other sources of radiation, such as naturally occurring isotopes. And while the limited sample size prevented any further investigation of this finding, Starosta emphasized that it remains interesting and unanticipated.

At the same time, he defends one conclusion about these radiations levels that is safe to draw: “From the point of view of human health, it’s completely insignificant.”