Chemicals from 50 years of oil sands production are showing up in increasing amounts in lakes in northern Alberta, a study says, with far-reaching effects.

Core samples from five lakes close to the oil sands mining and upgrading operations in Fort McMurray were analyzed by scientists at Queens University and Environment Canada for sings of cancer-causing chemicals like polycyclic aromatic hydrocarbons, Canadian Broadcasting Corp. reported Monday.

The chemicals can occur naturally, the scientists said, from forest fires, volcanic activity and geological deposits, but PAHs resulting from burning petroleum in the production of the oil sands leaves a particular fingerprint.

Levels of PAHs in all lakes studied had risen anywhere from 2 1/2 times to 23 times background levels measured in the early 1960s, before oil sands mining began in the region, researchers said.

These formerly pristine remote northern lakes now have the same chemical composition as lakes near urban areas, they said.

"This is an early warning indicator of what is happening," Queen's University biologist John Smol Said. "These lakes are not pollution pits by any means, but these wilderness lakes are similar to your typical urban lake."

Oil sands production in northern Alberta predicted to triple in the next 25 years will cause increases in these chemical deposits, the scientists said.

Long-term ecological effects of the PAHs as they are absorbed by fish, birds and up the food chain to humans is presently "unknown," they said.