The detection of an “alarming” amount of toxic emissions in a recent test has councillors and staff in Durham Region calling for more frequent testing of the controversial Clarington incinerator.

Among those pushing for more vigilance is the region’s chief medical officer of health, who told staff in an email obtained by the Star that the “sustained excessive emissions of dioxins and furans are a potential human health hazard, primarily by entering the food chain.”

Last month, Covanta, the company running the $289-million Durham York Energy Centre in Clarington, reported to the region that emissions from one of the two boilers at the plant exceeded the limits set by the Ministry of Environment for dioxins and furans by almost 12 times. Dioxins and furans are toxic byproducts that can result from burning waste.

The test triggered the process of informing the region and the ministry, said Paul Gilman, chief sustainability officer for Covanta. “We also decided to (shut) the unit down and start analyzing what had caused that exceedance during the test.”

Last week, Covanta provided both the region and the province with a detailed plan to determine the root cause of the toxic emissions and prevent it from happening again.

Mirka Januszkiewicz, director of waste management, said the region is waiting for Environmental Ministry approval of the plan.

While Covanta has been conducting a thorough investigation of the equipment, it “won’t be able to draw any conclusions about the root of the problem . . . until the boiler is back up,” she said.

Januszkiewicz said modelling of how the emissions disperse in the air showed there was no risk to humans. “We are very confident that . . . there was no impact to human health,” she said.

But in an email discussion between staff and Dr. Robert Kyle, the chief medical officer of health, Kyle called the test results “alarming” and expressed concern that the risk to humans was not through “inhalation but through ingestion” of dioxins and furans.

“With respect to human health, although the modelling results are reassuring, the main human health pathway of concern is ingestion, not inhalation,” said Kyle. “To this end, it is important for the local food chain to be protected by lowering dioxin and furan stack emissions and more frequent independent stack testing.”

A test of emissions last fall yielded similar results. At the time, both Covanta and the ministry said there was “interference” that led to the skewed results. The ministry accepted a retest in its place.

Januszkiewicz said that, this time around, the sample was tested in a different lab and the region had a peer reviewer check the test “to give us additional comfort” that it was done properly.

Earlier this year, York and Durham regions issued a certificate of acceptance that gave Covanta approval to operate the incinerator commercially and process up to 140,000 tonnes of household waste each year.

Clarington Councillor Joe Neal said his community is largely rural, and many fruit and vegetable farms are in the vicinity of the incinerator. “I don’t think the things should have been approved in the first place, given these outstanding concerns,” he said.

Linda Gasser, a Durham resident and long-time critic of the incinerator, said this test captures only a moment in time and may not provide a complete picture. “We don’t know the duration of this exceedance, and we don’t know how much has been emitted over the last six or seven months,” Gasser said.

The region said other testing, such as ambient air monitoring, continues to check emissions.

Januszkiewicz said her objective now is “to regain confidence of the public.”

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“I will be recommending more dioxins and furans testing,” she said. “But I am not the regulator, the Ministry of Environment is . . . and they are of the opinion that one test a year is meeting the regulatory requirement.” The region conducts one additional test, but had planned to do so only for the next three years. Clarington councillors want that period extended.

The Environment Ministry didn’t respond to questions from the Star.