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Researchers last year detected 3 tonnes of silver and 43 kg of
gold in effluent and sludge from waste water treatment plants -
amounting to around 3 million Swiss francs ($3.1 million).
But before people start hunting in their drains for jewelry, the
government study said the tiny particles were likely to be
mostly from the watchmaking, pharmaceuticals and chemical
industries, which use the metals in their products and
processes.
"You hear stories about an angry man or woman throwing jewelry
down the toilet, but we didn't find any rings, unfortunately,"
report author Bas Vriens said on Thursday.
"The levels of gold or silver were very small, in the
micrograms, or even nanograms, but when you add them up it's
pretty substantial."
Researchers are now studying if it is worthwhile to extract the
metals that end up in sewage sludge before usually being burnt,
but so far it has not found to be cost effective.
Higher levels of gold were found in the western Swiss region of
Jura, believed to be linked to watchmakers that use the precious
metal to decorate their expensive timepieces.
There was also a higher concentration in the southern canton of
Ticino due to the gold refineries in the area. This was the only
region where it might make sense to recover the metals, Vriens
said.
Other trace elements including rare metals such as gadolinium -
used in medical imaging - were also found by the scientists from
the government's institute of aquatic science and technology
(EAWAG).
Their discovery is the latest example of wealthy Switzerland
finding riches in unusual places.
Last month an investigation was launched after toilets at a
Geneva bank and three restaurants were blocked by about $100,000
in high-denomination banknotes - a bit different from the huge
fat mass that blocked an east London sewer.
The Swiss metal concentrations complied with regulations and
were removed before humans drank the water again, the study
said.
"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.
(Reporting by John Revill; Editing by Alison Williams)
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