A TRIUMF team led by Dr. Anne Trudel, Dr. Joe Mildenberger, and UBC Professor Emeritus David Measday completed precision measurements of low-level radioactivity concentrations in locally procured milk, rainwater, and bottled water. The tests gave conclusive evidence that the radiological impact of the Fukushima nuclear incident on BC is extremely limited and poses no health risk.
Four samples were assayed using TRIUMF’s specialized low-background radiation detection facility. One litre samples of commercial bottled water, rainwater collected on April 4, 1% milk, and homogenized whole milk were measured for periods of up to 15 hours.
Radioactivity concentration is measured in units of Becquerels per litre (Bq/l) in this type of measurement, which gives the quantity of radioactive decays per second in a given volume. Different radioactive isotopes are distinguished by characteristic energy signatures of the emitted particles. These low-level precision measurements require a careful analysis to distinguish radioactivity in the assayed samples from that due to naturally occurring backgrounds.
Iodine-131 was seen at 0.4 Bq/l level in rainwater and nothing at all at the 0.1-0.2 Bq/l level in the milk assays. Naturally occurring radioactive potassium-40 was observed at the level of about 40 Bq/l. The bottled water was included as a control sample because it was produced prior to the Japan earthquake and so should contain no contaminants from the damaged reactors.
These levels of radioactivity pose no health risks according to the BC CDC, Health Canada, and international standards prepared by the International Atomic Energy Agency. Health Canada reports that the typical potassium-40 level in milk across Canada is 50-55 Bq/l.
The specific results were as follows.
- Bottled water. No radioactivity was observed. Accounting for the overall sensitivities of the measurement, iodine-131 at a level of any more than 0.09 Bq/l would have been detected.
- Rainwater. The radioactivity identified was from iodine-131 at a concentration of (0.41 +/- 0.12) Bq/l.
- Local 1% milk. The only radioactivity was from potassium-40 at a concentration of (36.3 +/- 2.5) Bq/l. Potassium-40 is a naturally occurring isotope that is also present in bananas, avocados, and so on. Accounting for the overall sensitivities of the measurement, iodine-131 at a level of any more than 0.17 Bq/l would have been detected.
- Local homogenized milk. Radioactivity from potassium-40 was measured at a concentration of (40.5 +/- 1.6) Bq/l. Accounting for the overall sensitivities of the measurement, iodine-131 at a level of any more than 0.10 Bq/l would have been detected.
-- Edited by T.I. Meyer, Head of Strategic Planning & Communications