Why Millions of Dollars in Gold End Up in Sewers Every Year

Millions of dollars worth of gold and silver are flushed away in Switzerland each year, a new study has found.

More than $3 million of precious metals are found annually in sewage from more than 60 wastewater treatment plants in Switzerland, according to a study by the Swiss Federal Institute of Aquatic Science and Technology. Every year, about 95 pounds of gold and 6,600 pounds of silver are wasted, scientists said, adding that the annual totals were “quite substantial.”

In some areas of Ticino in southern Switzerland, where there are several gold refineries, “concentrations of gold in sewage sludge are sufficiently high for recovery to be potentially worthwhile,” the study says. But for the most part, scientists say the metals would not be worth recovering.

The concentrations of metals in most cases do not harm the environment, according to the study, which was commissioned by Switzerland’s Federal Office for the Environment.

While odd, it’s not particularly rare for sewage to contain gold. Other researchers have previously said at least $13 million in precious metals could be found each year in U.S. sewers. The metals can come from hair care products, detergents and nanoparticles put in socks to prevent bad odors, American researcher Kathleen Smith said in a 2015 study.

“There are metals everywhere,” Smith said at the time.