Increased levels of radioactive iodine have been detected in seaweed and rainwater samples in British Columbia and a scientist from Simon Fraser University says the Fukushima Daiichi nuclear reactor in Japan is clearly the source.
Krzysztof (Kris) Starosta, an associate professor in the department of chemistry at SFU, said levels of the radioisotope iodine-131 have risen, but are not a health concern.
Perry Kendall, British Columbia's provincial health officer, reinforced that view, saying the levels detected by SFU are "minuscule … very, very tiny," and are nothing to worry about.
He said the levels are "about one-millionth" the dose that would be of concern.
"We're looking at very low levels of radiation here," Dr. Kendall said.
Dr. Starosta agreed the levels are low, but he said they did climb over several days of testing as Japanese nuclear workers struggled to bring the damaged reactor under control.
"As of now, the levels we're seeing are not harmful to humans," Dr. Starosta said. "We have not reached levels of elevated risk."
He said the radiation is being carried across the Pacific to North America by the jet stream, strong wind currents that blow west to east high in the atmosphere. While most of the radioactivity falls out over the ocean, some of it has reached the West Coast where it is being deposited with rain. It is mixing with seawater and accumulating in seaweed.
The rainwater samples containing iodine-131 were taken at SFU's campus on Burnaby Mountain and in downtown Vancouver. Seaweed samples were collected in North Vancouver near the Seabus terminal.
Samples taken March 16 and March 18 did not show the signature for iodine-131, but it did show up in tests on March, 19, 20 and 25.
The radioactive substance is measured in "decays of iodine-131 per second per litre of rainwater," which is expressed as becquerels or Bq/l.
On March 18, the level was zero, but on March 19 it was 9 Bq/l and on March 20 it was 12 Bq/l. On March 25 the level was 11 Bq/l.
In Japan, a health warning was issued recently when iodine-131 levels reached 210 Bq/l in drinking water. The Japanese standard for iodine-131 in drinking water is 100 Bq/l if the water is to be consumed by an infant, and 300 Bq/l if the water is to be consumed by an adult.
"The only possible source of iodine-131 in the atmosphere is a release from a nuclear fission," Dr. Starosta said. "Iodine-131 has a half-life of eight days, thus we conclude the only possible release which could happen is from the Fukushima incident."
He said iodine-131 will probably continue to show up in B.C. for three to four weeks after the Fukushima nuclear reactor stops releasing radioactivity into the atmosphere.
Iodine-131 has been detected in rainwater at several locations in the United States in the past few days, but far below levels that would raise health concerns.
Dr. Kendall said health authorities will continue to monitor the situation, but it appears the fight to control the damaged reactor in Japan is being won, and even a worst-case scenario wouldn't threaten Canada.
"My sense is that it's coming under control. The amounts of radiation that were being emitted last week are probably not going to be measured again, unless something absolutely disastrous happens," he said. "Health Canada and the [Radiation]Protection Branch … have modelled with the U.S. other scenarios. They modelled one where a couple of the nuclear reactor cores melted down and three of the spent fuel-rod containments melted down - and even then we are at such a distance away, and there is such a volumetric dispersion, that we're not going to see levels of harm."