More than 10 years ago, scientists treated a remote experimental lake with the synthetic estrogen used in birth control:

The hormone all but wiped out the fathead minnows, a major food source for lake trout, the lake’s top predator. Carried out in Ontario, Canada, this experiment revealed hazards of water pollution that require no toxic waste dump—just excretion of common household drugs and other chemicals into the sanitation system.

“In remote lakes and especially in and downstream of urban and agricultural areas, there are often concentrated inputs of pollutants into watersheds,” says Jacques Finlay, a freshwater ecologist in the U of M College of Biological Sciences (CBS).

In Minnesota, CBS researchers like Finlay lead efforts to keep drugs such as oxycodone, heavy metals, insect repellent and the like from contaminating the waters we cherish—and waters around the world.

Here are two examples of how they’re doing it.

Enlisting bacteria

Metformin, a diabetes drug, is one of the most commonly detected drugs in waters worldwide. One way to rid waters of a pollutant is to enlist bacteria to degrade the drug—a specialty of genetic engineering pros like CBS professor Larry Wackett. His team discovered a bacterial gene that allows the microbes to degrade metformin.

Wackett and fellow CBS professor Tom Niehaus have now found six bacterial species that can break down the drug.

Why so many species? Bacteria routinely package genes in circular pieces of DNA called plasmids, which they pass around. Evidently, the genes for metformin degradation were shared between bacterial species this way. Because they have no loose ends for DNA-degrading enzymes to latch onto, plasmids lend stability to the genes that bacteria share.

Defeating ‘forever chemicals’

Chemicals known as PFAS (polyfluoroalkyl substances) pose perhaps the greatest challenge to efforts to detoxify our waters. They earned their moniker “forever chemicals” by being particularly hard to break down— a quality that made them popular for use in items like nonstick pans, raincoats, fire retardants, and heart valve replacements.

But by the time their links to cancer and developmental problems had been discovered, they had already spread widely in drinking water. PFAS molecules contain chains of carbon atoms of different lengths that are dotted with fluorine atoms. These molecules’ recent appearance in the world poses a difficulty for getting rid of them.

“Bacteria haven’t evolved the processes to break down forever chemicals,” Wackett explains. “But we do know of an enzyme that can break down smaller fluorinated molecules than the ones found in forever chemicals.” 

And his team is engineering a bacterium—species Pseudomonas putida—to digest the longer fluorinated carbon chains found in forever chemicals.

Also, because digestion releases fluoride that stresses the bacteria, Wackett’s team is engineering bacteria to become more resistant to fluoride—a job requirement for good PFAS degraders.