door handle
June 18, 2014

Sweat Counteracts Antimicrobial Properties Of Brass

Brett Smith for - Your Universe Online

Copper used in brass doorknobs and faucet handles has an antimicrobial effect, but when the hands touching these objects are sweaty – the effect can be mitigated, according to a new study in the journal Applied Surface Science.

"The antimicrobial effect of copper has been known for hundreds of years,” said study author John Bond, a forensic scientist from the University of Leicester, in a recent statement. “It is thought to occur as a result of a charge exchange between copper and bacteria, which leads to a degradation of the bacteria DNA.”

“We have discovered that the salt in sweat corrodes the metal, forming an oxide layer on its surface, which is the process of corrosion - and this corrosive layer is known to inhibit the effect of the copper,” he added.

To determine how corrosion from sweat might affect the antimicrobial properties of brass, the study team exposed the metal to various concentrations of aqueous NaCl formulated to replicate human sweat. Using X-ray spectroscopy and optical profiling, the study team analyzed the corrosive effect on their brass samples and found after one hour a 0.2 M concentration resulted in the formation of a zinc oxide layer. After 24 hours of exposure, the oxide film thickness was 1.3 nanometers.

"While it is well known that sweat corrodes brass, this is the first study to quantitatively analyze the temporal corrosion of copper alloys such as brass in the first few hours after contact between fingerprint sweat concentrations of salt and the metal,” Bond said.

"Opportunities to improve hospital hygiene are being investigated by the University of Leicester from seemingly un-connected areas of research,” he added. “This research is a different application of the study of fingerprint sweat corrosion of brass, applied to hygiene rather than to crime investigation.”

"My short term advice is to keep the brass in public environments free from corrosion through regular and thorough cleaning,” Bond suggested. “In the longer term, using copper alloys with corrosion inhibitors included in the alloy would be a good choice.”

"While more research is needed in the study of sweat and brass corrosion, anywhere that needs to prevent the spread of bacteria, such as public buildings, schools and hospitals should be looking at using copper alloy on everyday items to help in avoiding the spread of disease,” he concluded.

In the report, which Bond authored along with his Leicester colleague Elaine Lieu, the scientists concluded that their findings could be applied to forensics as well.

“Formation of oxide layers on brass by fingerprint sweat as observed here may well have implications for the successful investigation of crime by the visualization of corrosion fingerprint ridge patterns or the reduction of hospital environmental contamination by hand contact with brass objects such as door handles or taps,” the researchers wrote.

In March, Sally Davies, chief medical officer in England, warned about the rise of bacteria resistant to conventional antibiotics and called on the world governments to begin taking steps against the superbugs now.

“We haven’t had a new class of antibiotics since the late 80s and there are very few antibiotics in the pipeline of the big pharmaceutical companies that develop and make drugs,” Davies warned.