May 30, 2005

"Fingerprinting" methods help track contaminant sources, refine in situ cleanup

Groundwater researchers at the University of Toronto are developing pollution fingerprinting techniques that can not only determine the source of certain types of water contamination, they can also suggest more effective cleanup strategies.

Dr Barbara Sherwood Lollar, director of U of T's stable isotope laboratory, and her colleagues study the two leading types of groundwater pollution: petroleum hydrocarbons, from oil and gas spills; and chlorinated hydrocarbons, basic components of products such as dry cleaning fluids.

"Both of these two are important in that many of these chemicals are carcinogens, so they have important health impacts and they can very quickly deteriorate the quality of a groundwater resource," she says. "The other reason they're important is that they're so ubiquitous, there is not a community in Canada that does not have spills of one or another."

In studying these chemicals, Dr Sherwood Lollar and her colleagues break them down into a ratio based on the isotopes Carbon*12 and Carbon-13 that make up their molecules. Depending on where a chemical was produced, it will have a very specific carbon isotope signature.

"We can use it as an 'isotope fingerprint' to discern where the contamination is coming from," she says. "So, for example, if you've got a site where there's some question about whether it's coming from one neighbouring industrial facility or another, you can potentially use these Carbon-12 to Carbon-13 ratios to identify the source."

This ratio can also help improve 'in situ' cleanup techniques, which are increasingly favoured over what Dr Sherwood Lollar refers to as the "high engineered approach" to dealing with contaminated groundwater. Because the traditional method, in which the ground was dug up, the water pumped out, treated and returned, was costly and disruptive, there has been a move towards leaving the groundwater where it is, and either letting local microbes eat away at the Carbon-12 and Carbon-13, or introducing microbes from other areas to munch a path through the contamination.

Dr Sherwood Lollar's research contributes to this less invasive technique by determining which ratios will seem like a carbon buffet to different microbes, as they are picky eaters. "When the microbes consume these contaminants, they'd rather consume the lighter isotope, the Carbon-12, rather than the Carbon-13, because it's lighter and they can expend less energy to break the bond," she explains.

As an example of the success of this approach, one of Dr Sherwood Lollar's U of T colleagues, researcher Dr Elizabeth Edwards, discovered a microbe in soil from Kitchener, Ontario, that has been introduced to 20 other contaminated sites around the world.

More information is available from Dr Sherwood Lollar at 416978-0770, E-mail bslollar@chem.utoronto.ca.

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