Caesium 134 and caesium 137: The two isotopes that were released into the Pacific Ocean when an earthquake ruined the Fukushima Daiichi nuclear power plant on the eastern coast of Japan in 2011. The panic over the leakage was instantaneous in the US—but a new study shows whether it was valid.
Published in PNAS and pointed out by the LA Times this week, a years-long study by scientists at Canada's Bedford Institute of Oceanography proves just how long it took the "plume" to reach North America. The team from the Bedford Institute measured water samples for the presence of caesium 134 and caesium 137, beginning just a few months after the disaster.
They found nothing for many months—and the first instance of either caesium only appeared in June of 2013 along the Canadian coastline. What's more, the amount of material was miniscule. But we haven't reached peak caesium, as the LA Times says:
Computer models that match fairly closely with the hard data that Smith collected suggest that the amount of radiation will peak in 2015 and 2016 in British Columbia, but it will never exceed about 5 Becquerels per cubic metre.
Because of the structure of the currents, the radiation levels in Southern California are expected to peak a few years later, but by that time they will be even smaller than the highest levels of radiation expected in Canada.
Still, the scientists emphasise there's no need for concern. In fact, it's just going to be like going back to 1980s. "Cs levels in the eastern North Pacific from Fukushima inputs will probably return eastern North Pacific concentrations to the fallout levels that prevailed during the 1980s but does not represent a threat to human health or the environment," they conclude in their abstract. Meanwhile, the LA Times says the amount of material in the water along the coast of BC is still 1,000 times less than what the EPA defines as safe in drinking water. By the time it gets to California, it'll be even less. [LA Times; PNAS]