Tests have confirmed that a chemical linked to skin cancer spilled near Wabamun Lake after a train derailment last week, Alberta Environment says.

Aerial view of Wabamun Lake, covered in bunker fuel oil.

The department said Wednesday that initial results from samples taken near the lake showed a train car that was carrying about 70,000 litres of an oil used to treat utility poles leaked after the derailment.

It won't be known until later in the week whether enough of the substance spilled to pose a threat to human health, environment officials said.

The news that one of the CN cars was carrying a hazardous substance came to light four days after last Wednesday's derailment, when Alberta Environment officials noticed a green substance at the site.

They suspected it was a polycyclic aromatic hydrocarbon used to preserve wood, and which has been linked to skin and other types of cancers.

Initially, it was believed that only bunker fuel oil, a heavy oil used in asphalt production and to power ships, spilled into the lake. Crews are trying to contain more than 750,000 litres of the oil on the lake's surface.

CN Rail admitted this week that they'd known since Thursday that one of the derailed cars was carrying the pole-treating oil.

At a public meeting Tuesday, Doug Miller, CN's vice-president of transportation services, said they became aware of the car's contents when someone asked the company shipping the product for the material safety data sheet.

Asked why the information wasn't made public earlier, Miller said, "that was obviously a miscommunication." Residents booed.

CN spokesman Jim Feeny denied allegations that the company deliberately withheld the information, saying CN had worked hard to get details out quickly as it began to clean up the mess.

"CN would never purposely withhold information relating to public safety, but obviously we have an issue here with the specific information about this one specific car, about the contents of this one specific car," he said, adding CN officials are trying to determine who received the information and why it wasn't immediately passed on.

"Obviously there's been a disconnect here. We do know that there was a problem, that the information did not get to everyone who needed it."

The shore of Wabamun Lake.

The pole-treating oil was listed as lube oil on the shipping manifest.

Last Wednesday morning, 43 rail cars on a train travelling from Edmonton to Vancouver went off the rails as it rolled alongside Wabamun Lake.

The revelation that CN was aware of the car's contents before Alberta Environment became suspicious has further angered residents, already upset at the pace of the lake's clean up.

"Maybe there's something else in those rail cars that is going to come out today, or the day after," one man said at the meeting.

Residents have been told to not drink the water, or use it for showers or to wash dishes. Wabamun has been shipping its water in from Stony Plain.

Environment Minister Guy Boutilier is threatening CN with harsh penalties in connection with the spill, saying the company may have breached the law by not immediately disclosing exactly what was in the leaking rail cars.

"We have not been pleased with the work that has been carried out relative to what citizens have been telling us, and to what our inspectors have been finding," Boutilier said.

Alberta Environment spokesman Irwin Huberman says after the derailment, CN was obligated to give more details about what was in the cars and any potential environmental impact. The term "lube oil" is a general shipping category.

Wabamun Lake residents blocked the main line through their community for more than four hours Friday, protesting that the company seemed to care more about getting the track fixed than cleaning up the lake.

The track was reopened by Friday, while CN has brought in equipment from across the country to try to contain and clean up the spill. More than 9,000 metres of boom have been placed on the lake, but the slick has spread over at least eight kilometres because of wind.