Numbers, numbers, numbers...
2009 April 21
To The Editor,
Peace River Record Gazette:
To the Editor:
Quite often the nuclear debate derails into a discussion of numbers that few understand but somehow everyone feels must be discussed, when all along the real concern is not numerical but emotional: People dread this technology, and don’t trust the experts who say its safe. It’s a gut feeling which doesn’t go away with better-looking numbers.
Nevertheless, the numbers around tritium exposure were questioned here (“What are the numbers?”) so I thought I’d offer some observations.
As pointed out, Health Canada’s maximum drinking-water concentration for tritium is 7000 Bq/L. This means 7000 atoms of tritium disintegrating every second in a litre of water. For comparison, the background level of tritium in drinking water is 3-4 Bq/L, and each of us has about 10,000 Bq of a mixture of naturally radioactive elements in our bodies (mainly potassium and carbon, but also some uranium and tritium).
Health Canada’s drinking water standards for radioactive nuclides are designed such that if you drank only water contaminated at the maximum concentration every day for an entire year (at an average drinking consumption of two litres/day), you would receive the equivalent of about 3% of your annual background radiation exposure.
Put another way, a Canadian would have to drink 20-30 tonnes of water (20,000 – 30,000 litres) at the maximum contamination of tritium in order to equal his/her average annual background radiation exposure.
Now, in practice nuclear plants in Canada emit tritium at concentrations less than 1% of maximum Health Canada limit, so multiply the above numbers by another factor of 100.
Do other jurisdictions in the world have different drinking water standards for tritium? Sure, just like the driving age and other legal limits vary between provinces and countries. Your previous correspondent pointed out a few tritium limits that are lower than Canada’s (e.g. 740 Bq/L in the U.S.), but he neglected to include some that are greater: the World Health Organization (WHO) recommends 10,000 Bq/L, Australia uses 30,000 Bq/L, and Finland uses almost 80,000 Bq/L. So Canada’s limit is somewhere in the middle of global opinion.
Does it matter? If the radiation at these levels were remotely dangerous, maybe, but it’s not. As pointed out, these levels are comparable to the natural radiation in our environment, and well below anything known to cause harm. In fact, a large body of evidence suggests that radiation at this level, like hundreds of other natural agents encountered daily in our biosphere, is actually good for us.
Arguing about these miniscule levels radiation exposure is like trying to convince people to chew their food 100 times instead of 10 before swallowing. Does this make you ten times safer?
For more on Canada’s drinking-water standard for tritium, the Canadian Nuclear Safety Commission has an excellent fact sheet: www.nuclearsafety.gc.ca/eng/readingroom/healthstudies/tritium.
Dr. Jeremy Whitlock
"The Canadian Nuclear FAQ": www.nuclearfaq.ca