THUNDER BAY, Ont. - Premier Dalton McGuinty is urging forestry workers who were sprayed with cancer-causing toxins -- including Agent Orange -- decades ago to come forward.

"(It's) an important issue for us," McGuinty said Thursday while visiting Thunder Bay, Ont. "This has just recently been brought to my attention, I think probably to many inside government."

The government is trying to gather more information about what happened now that it has come to light that some workers were exposed to toxic herbicides while helping clear massive tracts of Crown land in northern Ontario.

"I think that this point in time, we're very interested in acquiring information," said McGuinty.

"And if anyone feels that their health has been compromised as a result of working with that particular compound -- it's something we no longer use obviously ... they should contact (the Ministry of Natural Resources) so we can begin to build a databank and assess what we're looking at here."

The Toronto Star reported Thursday that the Ontario government began experimenting with Agent Orange -- which was used to strip the jungles of Vietnam in the 60s -- in 1957.

Records from the 1950s, 60s and 70s show forestry workers -- often students and junior rangers -- spent weeks at a time as human markers holding balloons on fishing lines while low-flying planes sprayed toxins on the brush and the people below.

New Democrat Gilles Bisson, who represents the northern riding of Timmins-James Bay, said he was shocked to learn that the ministry knew Agent Orange had been used in the Kapuskasing and Hearst area decades ago, but remained silent.

"This is unbelievable," he said in a statement. "The Ministry of Natural Resources sat on this information and did nothing for years while northerners suffered ill health. This is the same chemical used in war."

Bisson said he wants complete disclosure of all documents related to the aerial spraying program.

"We need to identify those who would have been exposed to Agent Orange," he said. "It's only then that we can determine whether anyone has been affected."

The government should also start contacting people in the region so that it can begin studying the impact of the spraying program, he said.

"These people need to be tested," Bisson added. "And if cancer is detected due to those harmful chemicals, they need to be treated, and if necessary, compensation awarded."

Natural Resources Minister Linda Jeffrey said she's taking the matter "very seriously" and will share the government's findings with the public.

"To my knowledge, this is the first case of someone coming forward with these concerns, but I recognize that there could be others who have not yet contacted us," she said in a statement.

The ministry is taking "immediate steps" to gather as much information as possible on the government's use of the herbicides, but much of it predates electronic records and will take time to assemble and evaluate, she said.

She said the ministry raised the issue with Ontario's Chief Medical Officer of Health, Dr. Arlene King, last week and will keep her apprised any developments.

The Workplace Safety and Insurance Board has set up a dedicated phone line (1-800-387-0750, extension 4440) for anyone who may have questions and the minstry is making information available on its website, she said.

The Star said it obtained documents that showed the province experimented with a powerful hormone-based chemical called 2,4,5-T -- the dioxin-laced component of Agent Orange -- in Hearst, Ont. The documents, filed at the Archives of Ontario, describe how the planes had 140-gallon tanks containing the chemicals, which were usually diluted in a mix of fuel oil and water.

Less than a decade later, the Department of Lands and Forests -- now the Ministry of Natural Resources -- authorized the use of a more potent mixture of 2,4-D and 2,4,5-T for aerial spraying, the Star reported. The combination of those two herbicides in equal parts comprised Agent Orange.

Over the years, spraying was done by both the province and timber companies. Hundreds of forestry workers were involved, but the documents do not give an exact number, the Star said.

Bisson said medical studies show the type of dioxin found in Agent Orange latches on to fat cells and can remain in the body for decades.

Exposure could lead to skin disorders, liver problems, certain types of cancers and impaired immune, endocrine and reproductive functions.

Jeffrey said the ministry stopped using 2,4,5-T in 1979, and the federal government removed it from the herbicides registry in 1985. It's no longer used in Ontario, she added.