It's an unsavoury thought, but humans generate a lot of waste, and I'm not talking about your Christmas dinner leftovers. Sewage management is a massive undertaking and it has two branches. One collects rainwater and puts it back into the rivers, and one collects all the other, er, stuff, and channels it into the sewerage plants to be cleaned up. Unfortunately, sometimes these systems can get a bit mixed up, if, for example, there has been flooding, which causes some of the raw sewage to contaminate our fresh water sources that we use for drinking and bathing. So how do you test for this contamination? Well, this is where the tampons come it. The unique thing about tampons is that they're made from completely untreated cotton (so they don't hurt your ladybits), so they're great at picking up some of the chemicals that could potentially leak into the drinking water. What the scientists are looking for are mostly chemicals called "optical brighteners", found in laundry detergents, shampoos and toilet roll. These brighteners are put in to keep your whites white and are responsible for making white clothing glow under UV light. When a tampon comes into contact with even a tiny bit of optical brightener, it can glow under UV for up to a month. The scientists just continue to take measurements with (unused) tampons further and further upstream until they locate the source of the contamination. A fantastically low-tech solution for a difficult problem.
