Last week the French Institut de Radioprotection et de Sûreté Nucléaire (IRSN) reported that trace levels of the isotope had been detected in Northern Norway, Finland, Czech Republic, Germany, France and Spain.
IRSN pointed out that the detection of an element with a short - eight day - half-life indicates it must have been recently released.
The announcement prompted speculation about the source, with everything from secret nuclear weapon tests to unacknowledged releases from power plants being suggested.
However, the pharmaceutical industry is a more likely source according to Astrid Liland, head of section for emergency preparednessat the Norwegian Radiation Protection Authority(NRPA).
Liland told us: “A nuclear accident or detonation of nuclear weapons, would have resulted in many different radioactive elements at the same time. Since we only detected I-131 we believe it comes from a pharmaceutical facility.
“The only radioactive element detected was iodine-131, no other radioactive elements. This suggests a release from a facility producing radiopharmaceuticals. I-131 is frequently used for cancer treatment.”
This hypothesis fits with comments by the UK-based Society for Radiological Protection, which said: “the source of the release was not some sort of incident at a power reactor or other nuclear facility, but rather of medical origin, possibly a hospital or perhaps a supplier of radio-pharmaceuticals.”
To date no accidental releases of iodine-131 have been reported.
According to the NPRA a facility in Eastern Europe is a potential source of the isotope.
Lilandtold us “Based on the measurements across Europe and the winds at the time of detection, we think it originates somewhere in Eastern Europe. Since the winds were rapidly shifting during that time, it is not possible to pin-point where it came from.”