There is a strong possibility that the radiation detected in Ottawa biowaste last month came from the waste of medical patients, but the city's director of Water and Wastewater Services said it's impossible to know for sure.
The dose of radiation received from the bio-solids was extremely small -- less than 1/10,000 of what is normally received annually from natural sources, Dixon Weir said Tuesday.
The radioactive material is very likely the medical isotope iodine-131, but an investigation of the facilities known to use it failed to produce a source.
Similar situation have occurred in other cities in North America and Weir said the research points to "normal excreta that comes from people undergoing medical treatments."
"The situation is that what we have found, after much investigation, the biosolids here in Ottawa are consistent all over North America. They do not represent a risk to our works, the public or the environment," said Weir.
On Jan. 29, two truckloads of bio-solids from the R.O. Pickard Environmental Centre were turned away at the U.S. border after radioactive material was detected. Two more truckloads were discovered the next day at the plant. An investigation fail to identify the source and no other bio-solids have tested positive since then.
Weir said many trucks crossed the border without incident since then. The four truckloads are currently being held in quarantine while the radioactive material rapidly decays. He said a potential solution in the future is to just hold for a few days then take it over when it's no longer radioactive.