To recover it you do not even need a pick - all it takes is a dustpan and brush, according to Dr Hazel Pritchard, an exploration geologist at Cardiff University. "The nice thing about street dust is that it's already been crushed," she said yesterday. "All you would have to do is take the cigarette butts out."
The source of this potential 20th-century Klondike is the catalytic converters fitted since the Eighties to new cars. Each contains a couple of grams of platinum and other valuable metals such as rhodium, palladium and gold. The ratios of the metals confirmed that they were emitted from exhausts, Dr Pritchard said.
The best place to find platinum is in the mines of South Africa and Russia, where 10 tons of ore have to be crushed to produce just 1 ounce (28 grams). Yet the metal's value is so high, over pounds 200 per ounce, that it is economic to mine it at concentrations as low as 1,000 parts per billion (ppb). On a busy roundabout in Cardiff, Dr Pritchard found concentrations of up to 126ppb.
"I discovered that the concentrations were highest at roundabouts and in areas with expensive cars," she said. "It would be sensible to do a proper survey."
About 35 per cent of the world's total platinum output is used in catalytic converters, which turn exhaust gases such as nitrogen dioxide and hydrocarbons into nitrogen and carbon dioxide. They have been compulsory on new cars in Europe since 1993.
Extracting the metals would not be a simple matter of taking a vacuum cleaner to the nearest roundabout and then washing it out into the sink. "You would have to smelt it using nickel sulphide. It's not really the sort of thing you can do in your kitchen."
What's more, it is dangerous to kneel down and sweep busy roads. It can also surprise onlookers, as Dr Pritchard discovered: "I looked up from gathering these samples at 6.30 on a Sunday morning to find two paper boys looking at me in complete amazement."Reuse content