Researchers in Britain have found an unusual tool for tracking down sources of sewage pollution: Tampons. Glowing tampons, specifically. It's cheap and easy, and it works for the same reason that a white t-shirts have an alien glow under ultra-violet light:

It all comes down to Tide.

In Britain, a lot of old houses still have combined pipes to carry out their wastewater (the gross stuff draining out of your dishwasher and toilet) and surface water (accumulated rain water), so both go to a treatment plant to be cleaned of pollutants and waste. But newer houses sometimes have two sets of drains, with one system set to go right out into rivers and lakes in order to keep clean surface water from being unnecessarily treated.

But if you've ever been in a house where the hot taps on the cold side of the faucet, you can probably guess why this doesn't always work out: Sometimes someone hooks up the drains wrong and sends all the waste right back into the world untreated.

It turns out that tampons might be key to tracking down houses that have got their plumbing fouled up.

Professor David Lerner of the University of Sheffield found that the natural, untreated cotton used to make tampons as an excellent carrier of optical brighteners. Used in detergents, these chemicals make whites brighter by giving off subtle fluorescence. When you shine a UV light on white fabric full of brighteners, it lights right up with a blueish glow.

It turns out that tampons soaked in optical brighteners -- perhaps tied to sticks at the water's edge or to manhole covers -- make great little beacons for scientists to spot.

In a study published this week in the Water and Environment Journal, Lerner showed that unused tampons can glow for 30 days after just a five-second dip in a solution containing just  0.01 ml of detergent per liter of water.

Why do we want to make tampons glow? Well, we don't. Not really. But if scientists release these valiant hygiene products into the waterways and they start glowing, it's an indication that wastewater is being pumped in by accident -- because it's carrying detergent with it, among other things.

Sure enough, Lerner and his team were able to use the tampon test to figure out where the waste was coming from: When they got positive tests in what should have been clean water, they followed its pipes back and dipped clean tampons down each manhole until they found where the waste originated.

It may sound like a lot of work, but Lerner and his colleagues say it's cheaper and easier than many alternatives.

"Often the only way to be sure a house is misconnected is through a dye test - putting dye down a sink or toilet and seeing where the coloured water appears in the sewer," Lerner said in a statement. "It's clearly impractical for water companies to do this for all the households they supply, but by working back from where pollution is identified and narrowing it down to a particular section of the network, the final step of identifying the source then becomes feasible."

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