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In recent months, stories about sewers getting clogged have made international headlines. For example, a so-called "fatberg," a mass of grease and diapers, clogged London's sewers.
A new study has found stranger materials in a wastewater system: large amounts of rare and precious metals.
Researchers examined 64 wastewater treatment centers across Switzerland. A government press release says it was the first study on trace elements in wastewater in an industrialized country.
The researchers found 3000 kg of silver and 43 kilograms of gold in effluent and sludge from the centers. The value of the materials was somewhere around $3.1 million dollars.
The silver and gold were in the form of tiny particles. The researchers said the particles were most likely released during manufacturing of chemicals, pharmaceuticals, or watches.
Bas Vriens is one of the researchers. "You hear stories about an angry man or woman throwing jewelry down the toilet, but we didn't find any rings, unfortunately," he said.
"The levels of gold and silver were very small, in the micrograms, or even nanograms, but when you add them up it's pretty substantial."
The researchers also found large amounts of rare earth minerals.
The level of metal concentrations did not violate Swiss laws. They were removed before the water entered the drinking water system.
Vriens cautioned people against trying to find precious metals in drinking water. "It wouldn't make sense for people to boil their tap water to recover gold or silver because it has already been filtered out before it re-enters the drinking water supply," Vriens said.
I'm John Russell.
John Revill reported on this story for Reuters. John Russell adapted it for Learning English. Caty Weaver was the editor.
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