It's clear that Agent Orange was "very widely used" in Ontario for more than three decades and may have been used in other provinces and territories, the Ontario government said Monday.
A provincial probe into the chemical mixture that has been linked to certain types of cancer is now looking at its use by the provincial utility, municipalities and even farmers, said Natural Resources Minister Linda Jeffrey.
The herbicide 2,4,5-T - a dioxin-laced component of Agent Orange - wasn't banned by the federal government until 1985, which means it was widely used in Ontario, she said.
"When something is on a list that the federal government approves for use, all of us in Ontario would have used it, whether you were a private company, municipal government, provincial government," she said.
"Everybody was led to believe that this was a product that was safe to use."
Ms. Jeffrey urged federal Health Minister Leona Aglukkaq in a letter Monday to contact other provinces and territories to find out if they used Agent Orange as well.
The government has also contacted Hydro One and the Ontario Energy Board for more information about the use of Agent Orange along transmission lines.
The utility - which used to be called Ontario Hydro - used the toxic herbicide to clear power line corridors across the province from 1950 to 1979.
It was used on so-called transmission rights-of-way - the land on which large transmission towers stand, said Daffyd Roderick, a spokesman for Hydro One.
"As far as where precisely, we're co-operating fully with the Ministry of Natural Resources to investigate the use and understand better how it was used," he said.
Some Ontario farmers used the chemical along hedgerows and fence posts on the outskirts of their properties, but not on crops, Ms. Jeffrey said.
Her ministry is still collecting information from other departments and agencies that may have used Agent Orange as part of their operations, she said.
"Anybody who was interested in trying to keep down the brush and try to keep control over weeds at that point would have used the product," she said.
"At the moment, there are more questions than answers, and I'm working to try and find as many answers as I possibly can."
So far, it's come to light that the government used a mixture of two chemicals - 2,4-D and 2,4,5-T - to clear vast tracts of Crown land and control growth along highways during the 1950s, 60s and 70s.
The combination of those two herbicides in equal parts comprised Agent Orange - the most widely used defoliant in the Vietnam War.
The chemicals were federally approved at the time, but it is now known that exposure can lead to skin disorders, liver problems and certain cancers.
Former workers have come forward saying they were exposed to the chemicals and have suffered health problems as a result.
Those revelations prompted the government to launch its own investigation into its use of Agent Orange and announce plans for an independent panel to examine the issue.
In 2007, the federal government made $20,000 ex-gratia payments available to people whose health may have been harmed by the spraying of Agent Orange at Canadian Forces Base Gagetown in New Brunswick.
Premier Dalton McGuinty has pointed the finger at previous Conservative governments in Ontario for failing to tell workers about the dangers of Agent Orange. The premier and his ministers have even avoided uttering the words "Agent Orange."
The government needs to stop blaming others and reveal who might have been exposed to the chemicals, said NDP Leader Andrea Horwath.
"All people want to know is, where was it used?" she said.
"Let's get to the bottom of it, and then let's talk about how do we help the people who have been affected - those who have developed cancers and other kinds of illnesses as a result."
Opposition Leader Tim Hudak slammed Mr. McGuinty for "playing politics" with the issue ahead of the Oct. 6 provincial election.
"I know Dalton McGuinty is going to make all kinds of accusations, he's going to say all kinds of things to stay in the premier's chair," he said.
"I think it's going way too far when he suggests that somehow, spraying Agent Orange was a partisan issue."
But Mr. Hudak also acknowledged that his party knew about the use of Agent Orange months ago.
A constituent in a neighbouring Liberal riding contacted his office about his concerns over Agent Orange, Mr. Hudak said. His party didn't go public with the information because the constituent indicated that he was planning to bring those concerns to the minister.
The Canadian Press