An initial investigation at a sewage treatment plant in Ottawa indicates a commonly-used medical isotope is the source of low levels of radioactivity found in shipments of biosolids from the plant.

The City of Ottawa, however, says it can't confirm the discovery. Instead, city officials say they expect a report from a consultant in a week's time.

Two loads of the material, which were being sent to a New York company for composting, were stopped at the border on Jan. 29 because radioactive levels were too high. Two more truckloads of the sludge have also tested positive. The material has since been placed in a secure location.

"It's important to understand the levels that have been detected are very low," said Dixon Weir, the city's director of water and wastewater services.

The Canadian Nuclear Safety Commission says the identified isotope is "normally associated with waste from hospitals or persons who have undergone medical treatment." Officials are insuring the public there is no risk to the health and safety of Canadians or the environment.

Now, the commission says it will remind Ottawa hospitals of their responsibilities when it comes to disposing waste. However, hospitals CTV Ottawa talked to say they've been following the rules when it comes to waste disposal.

No radiation concerns, says consultant

Meanwhile, the city says a consulting firm it hired found no radiation concerns at the Robert O. Pickard treatment centre.

Six loads of biosolids passed inspection on Wednesday and were sent across the border to New York.

"They have been cleared and we think it's an anomaly at this point and even the testing we did on those loads, we're not finding anything to be concerned about," said Nancy Schepers, the deputy city manager.

Drinking water safe

Meanwhile, Ottawa city staff is reassuring residents their drinking water is safe.

"The city sampling program for drinking water occurs upstream of the Pickard centre. It's a very detailed program and we've gone back and looked through December and January records for gross alpha, gross beta and tritium and have not detected variations of significance there," Weir said.

Although concerns have risen over whether the incident is linked to a recent radioactive leak at the Chalk River nuclear plant in early December, the nuclear safety commission says the incidents are not related.

With a report from CTV Ottawa's Vanessa Lee and Joanne Schnurr