"You do get people looking at you strangely, but the tampon is not that obvious."

That's Professor David Lerner, explaining what it was like to conduct a research project where feminine hygiene products were inserted into streams and sewers around Yorkshire, UK. Why? It turns out tampons are an accurate and cheap way to sample water quality.

Towns and cities usually have two separate sewer systems. A sanitary sewer collects everything you flush or rinse down the drain, and transports it to a sewage facility for treatment. Storm sewers or overflow sewers collect up rain and runoff from roofs, paved roads, and parking lots. They empty that water into natural waterways like streams or rivers.

Storm sewers are not designed to handle untreated waste waters so it's important to keep what goes into them clean. "Grey water" contamination is a common problem – water from dishwashers, showers, and laundry that ends up in the storm sewer via incompetent plumbing or deliberate dumping.

Before you decide that grey wash water isn't that bad, as an FYI all sorts of non-lovely things live in your washing machine: norovirus and rotavirus; human pathogenic fungi; and of course a wide variety of fecal bacteria. Dishwashers are not much better.

Gwen Pearson

Laundry water looks pretty much like regular water. So how can you tell if a stream is contaminated? One way is to test for OBs, or Optical Brighteners (not to be confused with Obstetricians, or OB Brand tampons).

OBs are a regular additive to detergents that brighten whites and help hide yellow stains. They do this with a clever bit of visual trickery – an alternative name for optical whiteners is fluorescent whiteners. These compounds absorb invisible ultraviolet light and re-emit it as visible blue-white light, making your whites whiter. If you happen to have yellow stains on your shirt collar, the blue covers up the yellow via complementary color masking.

Optical brighteners do not occur naturally in rivers and streams, so they are a handy marker for contamination from human grey water sources. Brightening compounds glow brightly under UV light, so they're a clear indicator of pollution.

Fibre optic cables can be inserted into sewer systems to monitor contamination, but the cost is quite high–up to 9 £ ($13) per meter of sewer tested. Spectrophotometers can be used to detect contaminants, but they aren't cheap, and require training and calibration to use reliably. Testing an entire network of drains and sewers in a large urban area would be incredibly expensive in both time and equipment.

What Lerner and his research collaborator wanted was a simple, low-cost method for monitoring water contamination. Something that members of the public could do to to check their neighborhood streams. So the two Yorkshire engineers modified a US Environmental Protection Agency monitoring technique using cotton pads to be even simpler, smaller, and more portable: they used tampons as environmental samplers.

How to Make a Tampon Glow

Optical brighteners work because they are extremely sticky. Long after your clothes come out of the washer, the optical brighteners are stuck onto the fabric. The compounds build up with each washing, making your colors pop. And OBs will grab onto cotton in a stream or sewer, making it glow brilliantly under UV light.

Preliminary lab tests by the researchers confirmed that tampons quickly picked up optical brighteners at very low concentrations. Once they had their proof of concept, the scientists moved out into the field.

Tampons were placed in 16 surface water sewers, using the handy attached string to secure them to bamboo poles. After 3 days the tampons were retrieved and tested under UV light. And indeed, they did successfully detect grey water contamination, and determination of a positive and negative result was pretty clear. The total cost of sampling? An estimated 20 pence/tampon (30 cents in US Dollars), including the cost of the black light.

Gwen Pearson

Since the point of the research was to come up with a protocol suitable for use by regular citizens, I figured I'd give it a go. Indeed, I confirmed that you can get a brightly glowing tampon from short exposure in soapy water. (I would have tested this further in our local river, but I decided that explaining to my boss I was doing SCIENCE when I was arrested for littering by dangling tampons in the river was not a conversation I wished to have.)

Tampons are usually untreated cotton, so make an excellent, cheap sampling source. Grab a black light from your local party store and you are ready to sample for illicit waste water dumping.

Next, the plan is to roll out the procedure to community groups. Says Professor Lerner: "we're going to get a bunch of volunteers, we're going to go out and dip tampons in the river in as many places as we can throughout our watershed, and then work out which bits of the river might have pollution in them." A brilliant idea.

Dave Mark Chandler & David Nicholas Lerner. 2015. A low cost method to detect polluted surface water outfalls and misconnected drainage. Water and Environment Journal. doi:10.1111/wej.12112