Professor Lerner checking a stream in Sheffield with more typical, more expensive methods

“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…

OBs – optical brighteners – 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 $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…

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 each sampling? An estimated 30 cents including the cost of the black light…

This is what the military calls a field expedient. Like an improvised explosive device – the ever-popular IED so profligate in bits of the Middle East – any kind of field expedient can completely replace a more expensive traditional flavor of device.

After a couple of Yorkshire engineers complete larger, broadly inclusive testing, it sounds like another field expedient will enter the arsenal of water quality testing.