They also estimated that about 6,600 pounds of silver flows through those pipes, which is about $1.7 million, according to Bloomberg.
The study, commissioned by the Federal Office for the Environment, tested sewage in 64 wastewater treatment plants across the small country. While officials have long known precious metals get mixed in with sewage, they’ve never known exactly how much.
Eawag described it in a statement as “the first systematic, quantitative assessment.”
The precious metal most likely came from the country’s gold-refining plants and its watchmaking industry, slowly building up over a year. Switzerland is one of the world’s biggest gold-refining centers, with 70 percent of the world’s gold passing through its refineries each year, Bloomberg reported.
Gold prospectors shouldn’t get too excited. Eawag warned that the concentration of gold in most places wasn’t high enough to financially justify mining the toxic sludge.
But Ticino, an Italian-speaking region in the south of Switzerland, contains enough gold refineries releasing trace amounts of the metal into sewage pipes to make recovery there “potentially worthwhile,” according to the statement by Eawag.
Sewers in the United States might contain gold as well.
Researchers from Arizona State University published a similar study in 2015, finding that a U.S. city of 1 million people flushes up to $13 million worth of precious metals into the sewage system each year. Roughly $2.3 million of that is gold and silver.
Some countries work to retrieve the precious metals sloshing around under their streets. One wastewater treatment plant in Japan incinerates its sludge, extracting two pounds of gold from every 1,200 pounds of ash — an amount that Reuters said was “a higher gold yield from sludge than can be found at some of the world’s best mines.”
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