They call it filthy lucre, and for good reason. Cash collects germs faster than globe-trotting executives garner frequent flyer points.
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It’s easy to see why. More than almost any other physical goods, coins and bills change hands frequently, often moving from cash drawers to pockets and back several times a day. People fold them, flip them and even fondle them. They are frequently dropped and recovered, no matter how foul the surface they landed on.
And, with the exception of shady characters carrying suitcases full of illegal funds, few people in the West go to the trouble of laundering their currency. What gets dirty, stays dirty.
Not so in Japan, where the Hitachi company reportedly introduced an ATM machine in the mid-1990s that would sterilise bank notes, heating them to 200C (392F) before returning them to customers.
Anywhere else, beware the deli worker who takes change from the till while wearing plastic gloves, then goes on to make another sandwich without changing.
The problem of dirty dough was most recently highlighted by scientists Carla Carvalho and Maria Jose Caramujo at the Technical University of Lisbon, Portugal, who compared the bacteria on coins in their home city against those in Casablanca, Morocco.
Their results, reported in Microbiology Ecology, show surprisingly low levels, possibly because it’s hard for bugs to survive on dry metal surfaces. Almost half (44 per cent) of those they did find were Staphylococcus strains, and most were near the rims. More were detected on coins carried in pockets than on those that were taken from purses or wallets, which suggests that temperature and moisture are important factors.
It’s hard to show that anyone has actually fallen ill because of coins they handled, but equally it’s impossible to show that nobody has.
Public health officials have been aware of the problem for at least a century. Dr Thomas Darlington, New York’s Commissioner of Health from 1904 to 1908, was so alarmed by the results of experiments he conducted with bacteria on bills and coins that he told the House Committee on Banking and Currency “that it was desirable in the interest of public health that soiled bills be withdrawn from circulation as soon as practicable.”
Central bankers have been following his advice ever since, destroying 150,000 tonnes of soiled smackers annually while printing some 150 billion replacement notes at a cost of $10bn.
The new Governor of the Bank of England, Mark Carney, has decided to introduce plastic currency – as he did in his old job as Canada’s top banker – starting with a 5 pound note featuring Sir Winston Churchill to be issued in 2016.
But while plastic notes last longer, that just means they’ll have more time to accumulate the grime that is so attractive to germs. That grime is made of sebum, an oily substance that keeps hair and skin supple. Too much of it causes greasy hair. It’s also found in earwax. When bacteria break it down, it starts to smell.
Sebum, and the bacteria that feed on it, can be removed, usually with solvents, but that can damage security features such as holograms and magnetic or fluorescing inks. But a new technique developed by Spectra Systems, a company in Rhode Island, offers hope of a solution.
In an article published by Industrial & Engineering Chemistry Research, Spectra’s Nabil Lawandy and Andrei Smuk explain how supercritical CO2, raised to 60C at 5,000 PSI, where it behaves a bit like a gas and a bit like a liquid, can clean notes without damaging the anti-forgery measures.
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