The Cheat Sheet

Money may be dirty, but the rupee is among the cleanest

Venky Vembu | Updated on September 26, 2019

Is it because the rupee is well-laundered?

Very droll. I suppose you have Sharad Pawar on your mind when you say that cheekily.

I might have.

We’ll save that discussion for another day. For now, I’m talking about dirty money of the literal kind.

What about it?

Well, the annual Ig Nobel Prizes ceremony was held last fortnight at Harvard University, and…

Wait, don’t you mean the Nobel Prizes?

I most certainly don’t. The Ig Nobel Prizes, instituted in 1991 by the Annals of Improbable Research magazine, represent a quirky celebration of scientific and scholarly achievements “that make people laugh, and then make them think.” My nephew, who attended this year’s ceremony, says it was great fun, but also a tribute to unusual, offbeat research.

Where does dirty money come in?

This year’s Ig Nobel Prize in Economics went to three microbiologists — Habip Gedik (from Turkey) and Timothy Voss and Andreas Voss (from the Netherlands) — for their study to establish which country’s paper money carried and transmitted the most bacteria.

How did they study that?

In the first part, seven currencies were tested: the US dollar, the euro, the Canadian dollar, the Croatian kuna, the Romanian leu, the Moroccan dirham, and the Indian rupee. The banknotes were first sterilised and then inoculated with colonies of three types of bacteria under laboratory conditions; after a 24-hour incubation, all colony-forming units were counted, and the number of bacteria counted.

And the rupee…

...fared pretty well. The Croatian kuna came out the cleanest: it did not yield any of the three microorganisms that were sought to be transmitted. The rupee came in next best: it cleared two bacterial tests spotlessly (the Methicillin-resistant Stapylococcus aureus, or MRSA; and the extended spectrum of beta lactamasses (ESBL)-producing E.coli). It only failed the test for the Vancomycin-resistant Enterococcus faecium (VRE), a bacterium that may reside in humans and animals, and in its virulent form causes meningitis in babies and endocarditis, an inflammation of the heart valve. The cultures from the Romanian leu yielded all three multi-drug resistant pathogens.

Wow, so swachh rupee, huh?

Well, the Ig Nobel Prize-winning study was published in 2013, so credit may have to be widely shared.

So what accounts for the findings?

Unlike the rupee, the circulation of the US dollar, the euro and the Canadian dollar is not limited to one country, so they are more widely handled and more prone to bacterial transmission. But the banknote composition also matters.

Tell me more.

As the study Money and transmission of bacteria by Gedik et al recorded, banknote paper is typically manufactured from cotton fibre, which gives it strength, durability and a distinctive feel. The cotton is sometimes mixed with textile fibres. To give it extra strength, banknote paper is infused with polyvinyl alcohol or gelatin. Polymer (or plastic) banknotes were developed to improve durability and prevent counterfeiting. In the case of the Romanian leu, the polymer structure of the banknote allows growth and transmission of multi-drug resistant pathogens. “Countries using polymer-based banknotes should take this into consideration,” the study recommended.

Isn’t a country’s climate also a factor?

The experiments were conducted in the same laboratory conditions, using sterilised banknotes. To that extent, climatic conditions didn’t influence the findings. But, yes, in the real world, sweat, grime and general hygiene (or lack thereof) will determine whether your palms are greased by the ‘dirty money’ they handle.

A weekly column that helps you ask the right questions

Published on September 26, 2019

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