SINGAPORE: For the past two years, Dr Niranjan Nagarajan has been swabbing Singapore’s public spaces, from park benches to handrails at MRT stations, to study microbes present in urban areas that may make people sick.
There was one study, however, that this associate director at the Genome Institute of Singapore thought would be “scientifically very interesting to look at” and had not been done here, as far as he knew.
And that is to find out how dirty Singapore’s banknotes are. As his colleague Swaine Chen put it, money should be considered to be “just like another public surface”.
One such study in New York City, published earlier this year, found as many as 3,000 types of bacteria lurking on US$1 notes, including bacteria known to cause skin infections, gastric ulcers and food poisoning.
United States notes are made of cotton and linen, materials that support bacterial growth, while most of Singapore’s notes are made of polymer, which is less absorbent besides being able to incorporate security features that paper and cloth-based notes cannot.
Polymer notes can also last three to four times longer than paper money, according to the Monetary Authority of Singapore. But then are the Republic’s banknotes as sanitary as they are durable?
That theory has now been put to the test on Channel NewsAsia’s Why It Matters programme. Its producers sent 300 samples of banknotes to laboratories, to find out how clean they were. And the results seemed alarming. (Watch the episode.)
LIKE TOILET SEATS, SHOE SOLES
Some of the notes carried as much bacteria as found on the soles of shoes and on toilet seats – as well as more bacteria than on a smartphone and even the few “thriving colonies” on a kitchen sponge.
Those were the findings of senior lecturer and researcher Simon Tan, from the Singapore Polytechnic’s School of Chemical and Life Sciences.
The high bacterial count had to do with where the money was collected: Hawker centres, hospitals, supermarkets and wet markets across the country, with a good geographical spread.
Microbiologists from testing service provider ALS Singapore had processed the bacteria on the notes collected from over 100 locations, with money withdrawn from automated teller machines (ATMs) used as a comparison. The denominations ranged from S$2 to S$50.
And of all the samples, money from the wet markets had the highest bacterial count: An average of 48,000 on each note, which was almost 1,000 times more bacteria than the S$50 and S$10 notes fresh from the ATMs.
Notes from hawker centres had a bacterial count of 3,500, while it was 1,000 per note when it came to hospitals. Notes from supermarkets had an average count of 120.
Separately, an analysis was done on a single S$10 note to find out what DNA was left on it. The test revealed traces of animals like cattle, dog, fish, pig and sheep, besides human DNA and a lot of bacteria.
WET NOTES ATTRACT BACTERIA
Dr Chen, a senior research scientist, said the stalls selling raw meat and raw fish were the ones where the notes had the most bacteria from cross-contamination.
He contrasted this with places “not dealing with food, where they’re just storing cash”, such as ATMs and cash registers in supermarkets.
All bacteria need water to grow, he noted, so the “kinds of environments where bacteria tend to thrive are warm, moist, sometimes dark”.
He added: “If you have a wet note, and then it’s in your wallet, probably your body heat is providing the kind of perfect environment for bacteria to grow, as opposed to a dry note that was just warm.”
Watch: The investigation (2:28)
The question is how harmful these bacteria are. And here, Dr Chen said it was worth remembering that people come into contact with bacteria continually. “Things like yogurt and cheese have an awful lot of bacteria,” he pointed out.
According to him, it is not only the amount of bacteria but also the type that matters.
DEPENDS ON VIRULENCE, IMMUNE SYSTEM
In this case, one of the bacteria identified, E. Coli, is already found in the body, residing mainly in the gut, though certain strains can cause severe diarrhoea.
The bacterium staphylococcus, however, can be more serious. It is known to cause meningitis, which is the inflammation of the lining of the brain. “Some pathogenic strains may cause compromised patients to die in hospital,” warned Dr Tan.
“But if you happen to take a little bit of this, and you have a fully functional immune system as well as a digestive tract, you’d be okay.”
The bacteria can enter the body through a wound or be ingested if a person rubs his eyes or eats food using the same fingers that touched the notes, so washing one’s hands after handling money is advisable.
One thing is certain: More money is changing hands these days in Singapore, the world’s third-richest country.
In the past four years, the value of notes in circulation increased from S$30.3 billion to S$42.5 billion as at March 31, while the value of coins in circulation increased from S$1.3 billion to S$1.5 billion.
If all the notes are put side by side, they would go round Singapore’s coastline 633 times.
Said Dr Nagarajan: “Notes are constantly being exchanged between people, and it has a potential to transfer microbes to the recipient. And because of this, it’s of public health importance to understand what’s going on.”
Watch this episode of Why It Matters here (new episodes every Monday).