Although most of us know copper as a useful product for industry, fewer associate copper with health benefits. And yet those benefits have been well-documented since ancient times. Ancient civilizations exploited the antimicrobial properties of copper long before Louis Pasteur's discovery of bacteria. Copper was known to control infection in early Egyptian times. Even the bible suggests that the water stored in copper/bronze vessels was free of disease-causing agents.
In the Roman era, copper was mined principally in Cyprus hence the origin of the name of the metal, from aes Cyprium (metal of Cyprus). Cyprium later evolved to Cuprum (Latin), coper (Old English) and finally copper in modern English.
Copper (Cu) is a soft metal with very high thermal and electrical conductivity. Today copper is mostly found in electric wires, pipes and roofing. In addition to pure copper, there are also many important copper alloys. For example, the alloy of copper and nickel, called cupronickel, is used in low-denomination coins. The US five-cent coin currently called a nickel is actually 75% copper and 25% nickel. Other notable alloys are bronze (alloy of copper and tin) and brass (copper and zinc).
Copper is one of the few metals that can occur in nature in its native metallic form, which is why copper was one of the first metals to be used by humans. Some copper jewelry dates back to about 10,000 BC. Early copper tools such as axes have been found alongside stone tools at archeological sites in the Middle East and Europe.
The later Bronze Age (3750 to 500 BC) started in the Near and Middle East and spread to Europe by about 1800 BC. Objects made from manufactured brass, made by melting pure copper and pure zinc, appeared first in Roman times. Some Roman coinage from the reign of Augustus was made of bronze which was also used for Roman military equipment.
It is unsurprising that thousands of years of exposure to copper caused people to realize that the mineral has medicinal uses. Most common ancient medical treatments used copper salts and oxides, but solid metallic copper was used to treat a variety of disorders, including burns, itching skin, eye ailments and infected wounds. The Roman physician Celsus wrote a detailed description about the uses of copper filings, copper oxide and copper salts in his six volume series De Medicina. Pliny the Elder, a Roman author and naturalist observed in his Historia Naturalia that all kinds of ulcers are rapidly healed in individuals living or working in the vicinity of copper ores and mines.
Hippocrates, a Greek physician in Classical Greece who is considered one of the most outstanding figures in the history of medicine, recommended bronze for medical instruments, and indeed many ancient examples of bronze surgical instruments still survive today.
Interest in the medicinal properties of metallic copper waned in the early modern era, even after the French physician Victor Burq's statistical analysis of cholera mortality and morbidity during two Paris epidemics (1865 and 1866) found that only 16 deaths occurred among 30000 workers in the copper industry, while the death rate was 10-40 times higher among similar non-copper workers. Why copper protected those handling it against epidemics was never really followed up, especially after the discovery of antibiotics. The medical uses of metallic copper were largely ignored in the 20th century.
But copper is coming to the spotlight once again. Nowadays infection control and prevention is a major challenge in hospitals and other healthcare facilities. In 2002 an estimated 1.7 million people acquired an infection during a stay in a US hospital and 100,000 of these cases were fatal. The rise in drug-resistant strains has further complicated the problem, and this has caused many researchers to look at copper and copper alloys with fresh eyes.
There is mounting evidence that exposure to dry copper or copper alloy surfaces such as brass kills a wide spectrum of microorganisms including bacteria and fungi while also permanently inactivating several strains of virus. Multiple studies carried out in the last ten years show that microorganisms exposed to copper are killed almost completely (99.9%) within the first two hours. This even includes so-called superbugs, i.e. antibiotic resistant bacteria such as Methicillin-Resistant Staphylococcus aureus (MRSA) and Vancomycin-Resistant Enterococci (VRE).
With the recent pandemic of Coronavirus Covid19 (SARS-CoV-2), research showed that when sprayed on copper no viable SARS-CoV-2 was measured after 4 hours, yet SARS-CoV-2 s sprayed on cardboard persisted for up to 24 hours, and for 72 hours when sprayed on plastic or stainless steel surfaces.
Interestingly, it has been shown that pure copper is the best antimicrobial agent. With copper alloys such as brass, the higher the concentration of copper the better an antimicrobial agent it becomes. This means it is the copper part of the alloy which is essential.
Chemically, metals react with oxygen to form oxides and positive ions forming salts like CuCl2 and CuSO4 in case of copper. Copper ions are most commonly found in two oxidation states, Cu+ and Cu++, which are in equilibrium in solution in concentration copper.
Although the exact mechanisms are still debated, many studies suggest that 'contact killing' is initiated by the copper ions released from the copper surface by the culture medium and this causes cell alterations. A series of studies have concluded that the antibacterial effect of copper is related to its ability to release copper ions and their damaging effect on microbial cell membranes.
So it seems that we can still learn a lot from history and that copper may help to prevent infections in public places, especially in hospitals. A large clinical trial in Intensive Care Units in three American hospitals in 2013 showed that replacing plastic or stainless steel trays, call buttons and bed rails with brass substitutes was in itself enough to cut hospital-acquired infections by more than 50%.
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