Are Canadian fish being poisoned by radiation?

A news story has done the rounds on social media this year claiming that salmon in Canada had been found contaminated with radioactive isotopes from the damaged nuclear power plant at Fukushima in Japan.

Is it true? And, if so, is there anything to worry about? The answer to the first question is “yes, sort of”, but the answer to the second is “definitely not”!

The story grew from the fact that, in 2015, a single salmon caught in Osoyoos Lake in British Columbia was found to contain very low levels of a radioactive isotope called caesium-134.

The isotope is produced during nuclear fission – the process that drives both atomic power stations and atomic bombs. Because it has a half-life of about two years, any caesium-134 that was released into the atmosphere by previous bomb tests or reactor disasters (such as Chernobyl) has long since decayed away.

Therefore, any caesium-134 found in anything at the moment can only have come from Fukushima.

So, yes, a radioactive nasty from Japan did end up in a fish in Canada. However, there is much more to the story than that.

First off, scientists have always predicted that radioactive stuff from the damaged reactor would spread around the world, through the oceans and the air.

This is simply what happens. Between 1955 and 1963, for instance, there were a whole bunch of atmospheric nuclear bomb tests, which collectively pumped out a huge amount of an isotope called carbon-14.

All over the world, people who were children during that time have higher-than-average levels of it in their muscle tissues.

In 2016, caesium-134 from Fukushima was detected in the waters off the coast of northwestern US state of Oregon for the first time. This did not surprise environmental scientists and oceanographers, who had long predicted its eventual arrival. The isotopes detected in the sea were at very low levels and didn’t pose any threat to human health.

The same goes for the single Canadian salmon. In fact, the radiation levels detected in the fish were actually lower than the levels found in most other fish around the globe. This is because, every day, every living thing absorbs radiation produced naturally by cosmic rays, some kinds of rocks and minerals, and even the air itself. It’s called “background radiation” and it has been around since the Big Bang.

The suspect salmon wasn’t eaten, because it was used for testing. But if it had been, would it have made the person who ate it ill?

Not at all. The standard measurement for radiation in food is a unit called the becquerel. It is always expressed in terms of becquerels per kilogram.

The Canadian salmon contained 0.7 becquerels per kilogram. The World Health Organisation’s recommended safe maximum limit for radioisotopes in food is 1,000 becquerels per kilogram.

So, should you ever be lucky enough to find yourself hooking a sockeye salmon in Osoyoos Lake, have no fear. Wrap it in foil with a few slices of lemon and some thyme, chuck it on the camp fire, and enjoy!