From centuries-old time capsules to modern medical centers, copper shines as the metal of choice to preserve and protect. Case in point: A time capsule first buried in 1795 by Paul Revere and Samuel Adams was opened last week at Boston’s Museum of Fine Arts. The 10-pound box contained 24 copper and silver coins, a bronze medal, an inscribed silver plate, five newspapers, and other historical documents. The paper artifacts were remarkably well preserved, thanks in part to the copper coins included in the loot. Copper’s antimicrobial properties helped prevent fungus from eating away at the 220-year-old newspapers. As it turns out, copper is useful not only for preserving history, but for protecting human life as well.
Copper’s health benefits have long been recognized (Dollwet & Sorenson, 1985, cited in Grass, Rensing, & Solioz, 2011):
- Egyptians used copper to sterilize wounds and drinking water in the third millennium BCE.
- Greeks, Romans, Aztecs, and other civilizations used copper to treat headaches, burns, intestinal parasites, and infections.
- 19th-century Parisians noted that copper workers escaped cholera during outbreaks.
- Until the early 20th century, copper was used to treat chronic inflammation, eczema, lung infections, lupus, syphilis, anemia, and other conditions.
Copper’s popularity waned when commercial antibiotics became popular in the 1930s. However, recent battles with antibiotic-resistant “Superbugs” have sparked renewed interest in copper. The CDC reports that 722,000 infections were acquired during hospital stays in 2011, and about 75,000 infected patients died. Effects of copper surfaces on Salmonella, E. coli, MRSA, Staphylococcus and other scary microbes have been the focus of studies around the world. Some of these germs have been known to remain on surfaces for months (Grass, Rensing, & Solioz, 2011):
- A study in the United Kingdom found that bacterial contamination on copper or copper alloy (e.g., bronze and brass) surfaces measured 90%-100% lower than on plastic, chrome, or aluminum surfaces.
- A US Department of Defense-funded study of three medical centers found that copper alloy surfaces reduced the risk of hospital-acquired infections by more than half.
- Other hospitals around the world reported a 63%-71% decrease in bacteria on copper surfaces as compared to control surfaces.
Although copper’s success in diminishing infection-causing bacteria has been clearly established, the mechanism by which this is accomplished remained a mystery until recently. So how does copper kill germs on contact?
Attack the barrier! Copper kills microorganisms principally by destroying cell membranes. The electrical current of a cell membrane makes it effective in protecting the cell (read how polarity affects membrane integrity in our Membranes II module). Quaranta et al. (2011) found that copper interferes with the voltage of the cell membrane, depolarizing it. This compromises the barrier and causes the cell to die.
Kill swiftly. Microbes in contact with copper surfaces die at a rate of “tens to hundreds of millions of bacterial cells within minutes,” researcher Gregor Grass said in a 2011 American Society for Microbiology news release. This incredibly short time span doesn’t give cells a chance to divide and so prevents the organism from acquiring resistance to copper.
Take no prisoners. When the cell dies, copper destroys its DNA. Because the cell DNA is totally degraded, any potential resistance cannot be passed on.
Be the gift that keeps on giving. The Department of Defense study found that the microbe-killing action of the copper surfaces did not diminish over a two-year period. The self-sanitizing nature of copper makes it a natural weapon in the ongoing fight against increasingly tougher microorganisms. In fact, in 2008 the US Environmental Protection Agency listed copper as the first solid EPA-approved antimicrobial material, able to kill 99.9 % of surface bacteria.
Other studies report that using copper pans can reduce the spread of Salmonella during cooking and copper vessels can improve drinking-water safety, which could be particularly useful in developing countries. Opting for copper, bronze, or brass in hospitals, schools, public buildings, and homes—whether on frequently touched surfaces, in pots and pans, or in water containers—is an inexpensive, easy to implement, and low-maintenance mechanism for infection control when used along with standard hygiene practices.
And if you want your voice to be heard loud and clear in the future, toss a few pennies into a time capsule along with any papers you wish to preserve for posterity.
Grass, G., Rensing, C., & Solioz, M. Metallic copper as an antimicrobial surface. Applied Environmental Microbiology, Mar 2011; 77(5), 1541–1547.
Quaranta, D., Krans, T., Espírito Santo, C., Elowsky, C., Domaille, D., Chang, C., & Grass, G. Mechanisms of contact-mediated killing of yeast cells on dry metallic copper surfaces. Applied Environmental Microbiology, Jan 2011; 77(2): 416–426.
Read about the 1795 time capsule: “Coins, newspapers found as time capsule is opened,” The Boston Globe, January 6, 2015.
See a “Copper Fact-ite” sheet from the Geological Society of Australia.
Written by Bonnie Denmark
Bonnie Denmark holds an MA in linguistics and teacher certification in English, ESL, and Spanish. She has devoted her professional life to educational and accessibility issues as a computational linguist, multimedia curriculum developer, educator, and writer. She has also worked nationally and internationally as a language instructor, educational technology consultant, and teacher trainer. Bonnie joined the Visionlearning team as a literacy specialist in 2011, assisting the project by developing comprehension aids for science modules and creating other STEM learning materials.