Professor David Lerner carrying out pollution tests with tampons:

The cotton that makes up tampons is unique, in that it’s completely natural and untreated. As a result, the material is able to easily and effectively absorb different chemicals that it comes into contact with and clearly show the presence of these substances. Dr Lerner is using the feminine products, like litmus paper, to test for chemicals known as optical brighteners in freshwater. Found in laundry detergent, shampoos and toilet paper, these chemicals are used to keep items bright and white.

http://www.smithsonianmag.com/innovation/how-scientists-monitoring-water-with-tampons-180955008/