Researchers at Stanford have created a kind of inexpensive sensor based on carbon nanotubes (these things are so useful!) that can detect traces of TNT and the nerve agent Sarin in water. This can be useful to detect terrorist attacks on the water supply or leaching from munition making or storage facilities, but I bet this type of sensor could also be used to detect other kinds of toxins and help us track down polluters.
The beauty of those sensors is that they are much more sensitive than what we currently have (at least in that price range — it is possible to get very sensitive readings with expensive equipment).
Stanford writes: “The chip itself is made of an inexpensive, flexible plastic substrate, rather than the more expensive, rigid silicon that underlies most computer chips. The researchers also use a thin polymer gate electrical insulator layer, which allows the device to operate on less than 1 volt of electricity. […] In lab tests, LeMieux and Roberts found that when the chip was exposed to water with just 2 parts per billion of either TNT or dimethyl methylphosphonate (a sarin cousin), the chips instantly reported unmistakable changes in electrical current.”
If similar sensors could be made to detect various other pollutants, they could be deployed in the field and the data could be collected so that we’d have a real-time map of pollutants across whole regions (and eventually the planet), and we could better identify sources and see how they travel along ecosystems and the food chain. We could act before people and animals are poisoned. It would be really useful!