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Most of us don鈥檛 like to dwell on our toilet habits, but this week Crowdscience has gone down the drain to discover what wastewater can tell us about our health.

It鈥檚 been more than a year since scientists across the globe started to track the spread of Covid-19, with help from home test results and hospital data. Marnie Chesterton investigates the latest tool in their arsenal: sewage. Listener Kevin has heard how human waste can be monitored to check for virus levels, and wants to know if it can also be used to stop the disease in its tracks?

Although the coronavirus has been discovered in people鈥檚 poo, so far there鈥檚 little indication it鈥檚 actually being spread through the water system. But by taking regular samples from different parts of cities, authorities are now able to accurately predict a local peak weeks before the population shows signs of sickness, then take immediate measures to alert them. In Detroit we hear how environmental engineer Professor Irene Xagoraraki used this method to detect a rare strain of Herpes which doctors didn鈥檛 even know was a potential problem.

Marnie also talks to Professor Nick Thomson from the Wellcome Sanger Institute, who sequenced the genome of the bacteria that causes cholera, to understand how it has crisscrossed the globe. He discovered that the pandemic currently devastating Yemen actually originated in Asia. It鈥檚 a discovery that has changed how the WHO is thinking about this killer disease and could have important implications for vaccination programmes. But our effluent can also pose environmental problems, and Professor Andrew Johnson from the UK鈥檚 Centre for Ecology and Hydrology explains there are now as many as 300,000 chemicals that could threaten natural habitats.

While authorities try to test each one individually, he鈥檚 concerned they may have different effects when they mix in wastewater, and current monitoring systems don鈥檛 take this into account. Not only that, but some of these substances contain silver nanoparticles, which Professor Juliane Filser tells us stick around in soil for ever, threatening organisms and bacteria at the base of the food chain.

Presented by Marnie Chesterton and Produced by Marijke Peters for the 91热爆 World Service.

[Image: Sewage outlets. Credit: Getty Images]