01.10.07 - Turn on the tap ; flush the toilet ; take a shower. Water is a fundamental part of everyday life, and most of us take it completely for granted. Professor Tamar Kohn, however, doesn't. This environmental chemist knows that water never travels alone. Antibiotics, unabsorbed prescription medications, hormones, pesticides, herbicides, detergents, psychotropic drugs, disinfectants, and plasticizers all hitch a ride in this life-giving liquid as it goes down the drain.

Viruses can hang around for years in water looking dead, only to spring alarmingly into life when they encounter a host. Most of these contaminants are present in such minuscule quantities in our drinking water that we assume they don't pose a health threat. And they're so dilute that measuring them is almost impossible. But Kohn is determined to try.

In her Environmental Chemistry lab at EPFL, Kohn is collaborating with researchers at Universities of Geneva and Lausanne and the Swiss Federal Institute of Aquatic Science and Technology to develop the analytical tools needed to pin these tiny contaminants down. They've drawn up a list of the 60 most-wanted compounds that are relevant to Lake Geneva, and are working on measuring all of them simultaneously. When it comes to getting rid of them, Kohn looks to nature for inspiration, studying how natural water systems clean themselves up.

Are there natural processes taking place in the lake that remove contaminants ? If so, what can we do to promote them ? Kohn has found that sunlight plays a starring role : shining indirect light in water that is rich in organic matter causes a reactive species to form, which then gobbles up herbicides or other chemical contaminants. This kind of understanding could perhaps be used to design a low-cost treatment system that could treat water in developing countries. The soup recipe is complex : Kohn has discovered that getting the balance right requires a combination of (photo-) chemical and molecular biological methods managed on a case-by-case basis.

In another project, Kohn and her students are exploring how viruses die in surface water. As with other contaminants, she has found that the right combination of light and chemicals will kill a virus, but in this case her task is made difficult by the biological complexity of viruses. It's hard to tell if a virus is dead or alive-the only real test is to see if it infects someone. That runs into obvious ethical problems. The best way to deactivate a virus is to damage its protein capsule. Then, even with its DNA intact, the virus can't infect anything. Kohn is working on determining just how much of the capsule needs to be damaged to render the virus inactive. Fundamental understanding like this is extremely important in a world where water-borne pathogens kill millions of people every year.