Releases of radioactive tritium from Canadian nuclear power plants are so elevated that children under 4 and pregnant women shouldn't live within 10 kilometres of an atomic generating station, and those living within five kilometres shouldn't eat food grown in their gardens, Greenpeace says in a controversial study being released Tuesday.
Canadian-style Candu reactors are among the world's largest sources of tritium, producing up to hundreds of times more of the radioactive substance than other reactor designs. The report says high amounts of tritium in the Great Lakes and around the stations indicate nuclear plants routinely emit it into the environment.
The Greenpeace report calls Health Canada's standard for the level of tritium in drinking water "very lax" because it is about 10 times higher than that of the United States and 100 times higher than the level allowed in Europe.
"Scientific concerns about tritium's hazards are inadequately recognized by Canada's nuclear regulators," the study contends.
But federal regulators insisted Monday that tritium emissions shouldn't cause any concerns. The Canadian Nuclear Safety Commission said in a e-mail statement that tritium levels around atomic sites aren't a health threat and that the public "has not been exposed to unreasonable risk" from the consumption of fruits and vegetables grown near any facility. However, the commission said in January that its staff would study tritium emissions.
Most of Canada's nuclear power stations, located in Ontario, Quebec and New Brunswick, are in thinly populated rural areas, but the Pickering plant on the shore of Lake Ontario lies just outside of Toronto, and thousands of people live near it.
Greenpeace is the second influential entity to raise concerns about Canada's tritium standards recently. Last September, the Toronto Board of Health said it considered the drinking water standard out of date and it urged that it be tightened.
The Greenpeace study was written by Ian Fairlie, a British radiation expert who worked on a British government committee set up in 2001 to review the safety of tritium and several other radioactive substances. Earlier this year, he published a peer-reviewed journal article that concluded tritium's hazards are being underestimated.
Tritium, and the risk it poses, is among the most contentious topics in radiation safety. Tritium is a radioactive form of hydrogen, but is considered less of a cancer risk than substances such as radon that emit very large and damaging particles into cells when the elements decay.
However, some experts worry that tritium, because it is similar to hydrogen, binds readily with water and organic matter and therefore easily becomes embedded in living tissues, from which it can harm nearby cells.
In an interview, Dr. Fairlie said Ontario, with its large number of Candu stations, has some of the highest background levels of tritium in the world, and his recommendation about pregnant women living near nuclear plants was issued as a precaution, given the scientific uncertainty about its health effects.
He said the federal and Ontario government should establish an expert panel to determine whether the hazards of tritium need to be reviewed.
Canada considers drinking water containing up to 7,000 Becquerels per litre of tritium to be safe. A Becquerel represents one radioactive decay a second.
An Ontario government panel recommended in 1994 that the province set a drinking water limit of 100 Bq/L and then lower it to 20 Bq/L over a five-year period. But the advice, which would likely have led to occasional shutdowns of drinking water treatment facilities after radioactive releases at power plants, wasn't adopted. California recently set a goal of having drinking water contain 15 Bq/L or less, although this isn't a binding regulatory standard.
Small amounts of tritium are produced naturally in the environment, and pristine water typically contains about 2 Bq/L. However, water in both Lake Huron and Lake Ontario, where Candu reactors are sited, have about 7 Bq/L. The study said two-thirds of the radioactivity in the two lakes is from nuclear plant discharges.
According to the study, testing by the Ontario government found tritium in drinking water as high as 120 Bq/L on Lake Huron near one of the province's three nuclear plants.