As radiation from the Fukushima nuclear power-plant disaster drifted across the Pacific, fears that salmon and other marine life could be contaminated spread along the British Columbia coast.
But samples gathered by citizen scientists and a more comprehensive study done by Fisheries and Oceans Canada indicate the levels of radiation are so low they pose almost zero risk to human or ecosystem health.
Salmon remain safe to eat and the ocean is clean enough to swim in, say researchers who have been monitoring the arrival of the Fukushima contamination plume in British Columbia waters.
The most recent data come from a study led by John Smith, an oceanographer at the federal government's Bedford Institute of Oceanography, which confirms radiation from Fukushima has reached the continental waters of North America.
The study, published this week by the Proceedings of the National Academy of Sciences, notes that when the Fukushima disaster occurred during an earthquake-triggered tsunami in Japan, on March 11, 2011, significant amounts of radioactive cesium were released into the atmosphere and the ocean.
"The resulting large ocean plume of radioactivity dissipated rapidly … but a significant remnant was transported eastward," Dr. Smith's paper states. "By June 2013, the Fukushima signal had spread onto the Canadian continental shelf, and by February 2014 it had increased … resulting in an overall doubling of the fallout background from atmospheric nuclear weapons tests."
Dr. Smith predicted the radiation will peak in 2015-16, and then start declining, but it will never reach levels high enough to cause concern.
Measuring the radiation in a unit known as a becquerel, Dr. Smith reported even at its highest the total levels of cesium off the North American coast will likely not exceed three to five becquerels per cubic metre of seawater. By comparison, the acceptable standard for drinking water in Canada is 10,000 becquerels per cubic metre.
Dr. Smith also wrote that while radiation does collect in fish, the "predicted exposure level is many orders of magnitude less" than the baseline safe levels.
As scientists tracked the Fukushima plume across the Pacific, concerns arose that radiation could build up in salmon, clams and other marine animals harvested on the B.C. coast.
"Some people are not eating their fish because they're scared," Annita McPhee, then-president of the Tahltan Central Council, said last year.
Ken Buesseler, a researcher with the Woods Hole Institute, said in an interview Tuesday that it was such public concerns that persuaded him to help launch a citizen science program that is monitoring water along the West Coast from Alaska to California. There are several testing sites in British Columbia and last month the program announced detecting trace amounts of cesium from the Fukushima accident in California waters.
Dr. Buesseler said the citizen science study and the new research by Dr. Smith should reassure the public.
"I think this is a very insignificant risk," he said of the radiation levels being detected. "Swimming in water like this every day of the year is a hundreds of time lower dose … than a single dental X-ray."
Jay Cullen, a University of Victoria chemical oceanographer, is leading the Integrated Fukushima Ocean Radionuclide Monitoring (Inform) program, which is working jointly with Woods Hole, Fisheries and Oceans and others to study the radiation plume.
Dr. Cullen said Dr. Smith's report shows radiation levels lower than those in the 1960s, when nuclear-weapons testing caused readings of up to 80 becquerels per cubic metre of seawater.
"When we look at fish we depend on culturally in B.C., like salmon, we don't expect the impact to be measurable," he said. "The danger to the public and the marine environment is very low."