Toxic human waste could provide a new source of recoverable gold worth hundreds of millions of dollars, according to US scientists. Researchers discovered microscopic nuggets of gold, silver and platinum after examining human solid waste using an electron scanner at American sewage plants.

If the findings – and anticipated commercial refinement process – are realised, the waste products from just one million Americans could be worth as much as US$13 million, a new study published in the journal Environmental Science and Technology has revealed.

According to the BBC, the results were made public at the 249th national meeting of the American Chemical Society (ACS) in Denver, CO.

“The gold we found was at the level of a minimal mineral deposit,” lead scientist Dr Kathleen Smith said.

Gold was not the only precious metal found. The researchers also found traces of rare earth metals palladium and vanadium, used in mobile phone and laptop technology.

“We’re interested in collecting valuable metals that could be sold, including some of the more technologically important metals, such as vanadium and copper, that are in cell phones, computers and alloys,” Dr Smith told the audience.

The team estimates that seven million tonnes of bio-solid waste comes out of US waste water facilities each year. About half of that is used as commercial fertiliser on farms, fields and in forests. The other half is incinerated or sent to landfills.

The scientists are experimenting with some of the same chemicals, called leachates, which industrial mining operations use to pull metals out of rock.

While some of these leachates have a bad reputation for damaging ecosystems when they leak or spill into the environment, according to Smith a controlled setting could safely be used to recover metals in treated solid waste.

In a two-pronged investigation, scientists are examining removing the useful minerals for profit and those harmful minerals that prevent the waste being reused.

“If you can get rid of some of the nuisance metals that currently limit how much of these biosolids we can use on fields and forests, and at the same time recover valuable metals and other elements, that’s a win-win,” Dr Smith said.

In a previous study, another team of scientists calculated that the waste from one million Americans could contain as much as $13m (£8.6m) worth of metals.

Additional reporting by Press Association