But the sewage pipes are packed with it.
Millions of dollars worth of gold and silver are flushed away in Switzerland each year, a new study has found.
The concentrations of elements pose no risk to the environment as most cases lay below harmful limits. Scientists have long known that small amounts of the valuable metals can wind up mixed in with sewage.
The scientists found other unexpected elements in the water: large amounts of silver and even rare earth minerals often used in the manufacture of electronic devices. While this may not seem much at first glance, the nationwide fluxes expressed in kilograms per year are quite substantial - 3000 kg of silver, 43 kg of gold, 1070 kg of gadolinium, 1500 kg of neodymium and 150 kg of ytterbium (see Table S9 in the original publication).
But the concentrations of metals varied across the country.
Switzerland's gold refineries may want to consider starting a recycling program. In southern Switzerland, though, where gold refineries are concentrated, enough gold is being wasted that it could be worth recovering from the sewage stream.
Scientists conducting the research say around 95 pounds of the rich material is flushed through the Swiss sewage systems each year.
The gold, the researchers believe, comes from "tiny flecks of gold"-residue from the country's watchmaking industry and gold refineries". The USGS has explored ways to remove potentially unsafe metals from treated sewage that is used as fertilizer, and also pursued the possibility of extracting valuable metals from wastewater as a potentially profitable resource. A group of researchers led by Eawag environmental chemists Bas Vriens and Michael Berg has now carried out the first systematic, quantitative assessment of elements discharged in effluents or disposed of in sewage sludge.