"Over the last couple of generations, there has been a huge amount of ground water pollution worldwide, and this has had a negative impact on our drinking water supply," says Barbara Sherwood Lollar, Canada Research Chair in Isotope Geochemistry of the Earth and the Environment at the University of Toronto. Her research examines society's efforts to reverse and stop ground water pollution, and the effectiveness of bioremediation technologies – using microbes to clean up organic contaminants such as petroleum hydrocarbons (oil, gasoline or diesel) or chemicals used in the electronics or transportation industries.

While the disposal of these organic contaminants tends to be well regulated today, this has not always been the case. Lax regulations and enforcement during the period immediately after World War II has left Europe and North America with a legacy of past contamination.

"This contamination has had a pervasive impact on the environment," says Sherwood Lollar. "It is still out there, and it needs to be dealt with."

Over the past decade, many techniques used to clean up ground water contamination have harnessed the power of microbiology and the work of geochemists like Sherwood Lollar. "We are not genetically engineering microbes," she explains. "In many settings, naturally occurring microbes feed off the organic contaminants and, in the process, convert them to non-toxic end products."

Until now, the real difficulty has been in proving that the process exists and that the microbes actually are cleaning up the contaminants. Sherwood Lollar has developed techniques that show where the clean-up is happening and, just as importantly, where it is not.

"Elements like carbon have different stable isotopes: Carbon-12 and Carbon-13. One is slightly heavier than the other, and the microbes tend to feed mostly on the lighter one. When the microbes have been working for some time, the ratio of heavy-to-light carbon will change. It is this change – referred to as an isotopic signature – that lets us know the water is being cleaned up," says Sherwood Lollar.

By cleaning up contaminated ground water, it is possible to recuperate what otherwise would be a lost resource. The technique is starting to be used by regulators, and Sherwood Lollar is working with an international group of scientists to put together a guidance document for the United States Environmental Protection Agency (EPA).

This will provide a set of recommendations about use in the field for practitioners, which will be a first step towards mainstreaming the technique.

"It's a common misconception that water – and especially our supply of ground water – is a renewable resource," says Sherwood Lollar. "But it isn't. So, it is particularly important that we manage it well and that we do whatever we can to conserve, protect and remediate what we have."