August 2008- Who knew the Statue of Liberty was so hygienic? Turns out, the iconic statue might just be a germ-killing giantess as its main element of composition, copper, has proven to be a surprisingly antimicrobial metal.

The EPA recently approved the registration of antimicrobial copper alloys, with claims that recognize the metal's proficiency in killing dangerous, disease-causing bacteria. Copper is the first solid surface material to attain this sort of registration, after extensive testing proved it could kill antibiotic-resistant "superbugs" like the virulent Methicillin-resistant Staphyococcus aureus (MRSA).

Stainless, not germless
Initial research at the Copper Development Association (CDA)into copper's antimicrobial properties began in 2001 and by 2005, the organization announced its findings. It found that copper could inactivate 99.9 percent of MRSA strains in 90 minutes. Brass killed the bug in 4.5 hours, and a copper-zinc-nickel alloy saw significant reductions in the same timeframe, but after 72 hours on stainless steel, some MRSA bacteria still remained alive.

"In contrast to copper alloys, stainless steel has no intrinsic antimicrobial properties," says Dr. Harold Michels, senior vice president of technology and technical services at the CDA. "In fact, stainless steel is the EPA-mandated experimental control. And, looks can be deceiving. While stainless steel looks clean, it may be contaminated with lots of bacteria--some of which would be dead on a copper alloy surface."

The bacteria used in the EPA testing, along with MRSA, included normal Staphylococcus aureus, as well as Enterobacter aerogenes, Escherichia coli O157:H7 (E-Coli), and Pseudomonas aeruginosa. Other disease-causing microbes that were shown to be inactivated by copper through independent CDA tests include the bacteria Clostridium difficile; Listeria monocytogenes and Acinetobacter baumanni; the virus Influenza A; and Aspergillus niger, a common black mold.

The oxidization of copper seems to lessen its bacteria-killing effects, and alloys with lower copper content take slightly longer to inactivate microbes. Whereas a pure copper alloy like C110 kills bacteria within an hour, C260 brass, which has 70 percent copper, takes closer to two hours.

New applications
The rapidity of copper's microbe-killing, especially in relation to stainless steel, traditionally considered a "clean" metal and widely used as surface material in hospitals and clinics, has far-reaching implications.

"Since reservoirs of these particular microbes can build up on just about any surface with which the public may come into contact, the uses for copper alloys are many and varied," says Dr. Michels. "We see it being used in public buildings, fitness centers and spas, schools, nursing homes, public transportation systems and more. Specifically, on handrails, door knobs and other furniture hardware, faucets, sinks, floor/wall/ceiling tiles, water fountains, instrument handles, toilet/urinal hardware, light switches, etc. Simply think about all of the surfaces you might touch in a day."

According to the CDA, discussions with major hospital equipment managers about ways to manufacture and implement copper-based products are ongoing. MM