The two studies from the University of Waterloo couldn't find any increase over time of toxic hydrocarbons or heavy metals in sediments from lakes and rivers on the Athabasca Delta north of the oilsands mines.
"We observe no measurable evidence of related far-field airborne metal contamination in the Peace–Athabasca Delta located (about) 200 km to the north," says one of the studies published in the online journal PlosOne.
The other study, published in Science of the Total Environment, comes to a similar conclusion about hydrocarbon deposits in lakes downstream of the mines.
"Despite rapid growth of oilsands development during the past 25 years, the data reveal no measurable increase in concentration or proportion of river-transported bitumen-associated indicator (hydrocarbons)."
That study says the Athabasca River remains a major source of hydrocarbons in the environment as it erodes through the same deposits being mined.
The studies were funded by oilsands giant Suncor. The scientists said other sources of funding were unavailable and Suncor didn't influence either the design of their work or its conclusions.
Other widely cited studies have previously found significant contamination within a 50-kilometre radius of oilsands developments, which are numerous in northeastern Alberta. More are planned.
The scientists used sediment core samples from riverbeds and lakes going back more than 200 years. While the teams found that levels of toxic heavy metals such as lead, arsenic and mercury have fluctuated over the years, those changes didn't seem associated with oilsands activity.
"Enrichment of these metals peaked between 1950 and 1970 (at about 30 to 45 per cent above pre-industrial values) and has been declining since," one of the reports says. "Mercury enrichment began about two decades later (post-1940s), peaked between 1965 and 1990, and has since declined."
The other study used a similar method to examine hydrocarbon deposits in several lakes downstream from the oilsands in the Athabasca Delta. The scientists said they couldn't find an increase in those deposits since oilsands mining began.
"Natural processes responsible for delivering bitumen from along the banks of the Athabasca River and its tributaries can account for the (hydrocarbons) most associated with a bitumen origin."
The report acknowledges its conclusions are based on sediments drawn from a single lake, but adds that the lake is in an area where it should be a good indicator of what's in the sediments.
Some of the conclusions are being disputed by other scientists.
Peter Lee and Kevin Timoney, who published a 2011 paper arguing that industry has increased contaminant levels from the oilsands, said in a commentary that the Waterloo papers still don't distinguish between natural and artificial sources of bitumen in the water. They say the study area is far too small and the data too limited to support the conclusions.
"The authors admit that their interpretation is based on essentially one basin and, later in the paper, the authors recommend that sediment sampling be conducted at 40 basins."
The Waterloo papers acknowledge the need for more research on whether contaminants in the Athabasca are naturally occurring or the result of industry.
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