It has been known for centuries that silver kills germs. Having silver service, for example, was practical as it had been known since Roman times that silver vessels preserved wine. But silver is also formidably effective against both bacteria and viruses.
In its colloidal and salt form, silver has been used in “alternative” medicine for decades but was commonly used in mainstream medicine before the discovery of antibiotics in the 1940s.
Copper has a similar effect; a brass doorknob for example will self-disinfect itself in less than eight hours whereas stainless steel will not. Copper in concentration is toxic but silver is not toxic to mammals as it passes through the body excreted in urine.
Paradoxically, it is the increasing emergence of microbes resistant to antibiotics that has lead directly to the interest in silver as an antimicrobial agent again.
How it works is still not well-known. It is presumed that silver ions can penetrate the outer cell wall of microbes and cause them to dehydrate. Microbes are not able to develop resistance to silver and it is possible to coat surfaces with a solution of suspended or colloidal particles or nano-particles that will work indefinitely.
Nano-particle science has developed silver in antiperspirants and the bonding of silver to polymers—this allows clothing that acts on odour-producing bacteria (useful for gym wear).
Lately silver nano-particles have found their way into paints after scientists discovered a way to prevent the particles from clumping together. The active ingredient is not used up so the paint continuously kills any bacteria, mould or virus that lands on the treated surface. This is especially effective in damp, humid and warm places such as kitchens and bathrooms. In New Zealand Resene is the only major paint company to date to have released such paint to the retail market.
Paint containing silver particles is becoming widely used in hospitals where it is known to be effective against methicillin-resistant staphylococcus aureus (MRSA) and other resistant organisms. Silver-impregnated plasters and compounds of silver (silver sulfadiazine) are undergoing a return to popularity in the health system for treating burns and wound infection.
Samsung recently released a washing machine with a bowl treated with silver to disinfect as it washes. Water tanks on ships are often “silvered” to keep the water potable over long periods. Commercial solutions available to treat domestic water tanks have proven very effective.
Concerns have been raised about the leaching of silver particles into the sewage treatment facilities where they could destroy the very bacteria that help to digest and breakdown sewage. There are also some fears about the ingestion or skin absorption of these particles. This in spite of evidence of people consuming very high concentrations of colloidal silver for years with no real ill-effect other than a tendency to turn an unappealing shade of blue-grey, a condition known as argyria.
There is ongoing research into methods of bonding the silver permanently to polymers and other substrates to prevent leaching. In general, the amounts that leach from textiles or even silver washing machines are vanishingly small and occur only at the first wash. Thereafter they are all but undetectable.
It seems certain that silver will play an increasingly important role as a replacement for antibiotic chemicals and drugs and its use in textiles and other substrates will increase. Controlling leaching into the environment will be a concern, but no more than controlling the current tide of drug residue and hormone disrupters presently poisoning our environment.