The oligodynamic effect (from Greek oligos, "few", and dynamis, "force") is a biocidal effect of metals, especially heavy metals, that occurs even in low concentrations.
In modern times, the effect was observed by Carl Nägeli, although he did not identify the cause. Brass doorknobs and silverware both exhibit this effect to an extent.
Mechanism
The metals react with thiol (-SH) or amine (-NH(1,2,3)) groups of proteins, a mode of action to which microorganisms may develop resistance. Such resistance may be transmitted by plasmids.
List of uses
Aluminium
Aluminium triacetate (Burow's solution) is used as an astringent mild antiseptic.
Antimony
Orthoesters of diarylstibinic acids are fungicides and bactericides, used in paints, plastics, and fibers. Trivalent organic antimony was used in therapy for schistosomiasis.
Arsenic
For many decades, arsenic was used medicinally to treat syphilis. It is still used in sheep dips, rat poisons, wood preservatives, weed killers, and other pesticides. Arsenic is poisonous if it enters the human body.
Barium
Barium polysulfide is a fungicide and acaricide used in fruit and grape growing.
Bismuth
Bismuth compounds have been used because of their astringent, antiphlogistic, bacteriostatic, and disinfecting actions. In dermatology bismuth subgallate is still used in vulnerary salves and powders as well as in antimycotics. In the past, bismuth has also been used to treat syphilis and malaria.
Boron
Boric acid esters derived from glycols (example, organo-borate formulation, Biobor JF) are being used for the control of microorganisms in fuel systems containing water.
Copper
Brass vessels release a small amount of copper ions into stored water, thus killing fecal bacterial counts as high as 1 million bacteria per milliliter.
Copper sulfate mixed with lime (Bordeaux mixture) is used as a fungicide and antihelminthic. Copper sulfate is used chiefly to destroy green algae (algicide) that grow in reservoirs, stock ponds, swimming pools, and fish tanks. Copper 8-hydroxyquinoline is sometimes included in paint to prevent mildew.
Paint containing copper is used on boat bottoms to prevent barnacle growth (biofouling).
Gold
Gold is used in dental inlays and inhibits the growth of bacteria.
Lead
Physicians prescribed various forms of lead to heal ailments ranging from constipation to infectious diseases such as the plague. Lead was also used to preserve or sweeten wine. Lead arsenate is used in insecticides and herbicides. Some organic lead compounds are used as industrial biocides: thiomethyl triphenyllead is used as an antifungal agent, cotton preservative, and lubricant additive; thiopropyl triphenyllead as a rodent repellant; tributyllead acetate as a wood and cotton preservative; tributyllead imidazole as a lubricant additive and cotton preservative.
Mercury
Phenylmercuric borate and acetate were used for disinfecting mucous membranes at an effective concentration of 0.07% in aqueous solutions. Due to toxicological and ecotoxicological reasons phenylmercury salts are no longer in use. However, some surgeons use mercurochrome despite toxicological objections. Mercurochrome is still available to purchase in Australia to use on minor wounds. Dental amalgam used in fillings inhibits bacterial reproduction.
Organic mercury compounds have been used as topical disinfectants (thimerosal, nitromersol, and merbromin) and preservatives in medical preparations (thimerosal) and grain products (both methyl and ethyl mercurials). Mercury was used in the treatment of syphilis. Calomel was commonly used in infant teething powders in the 1930s and 1940s. Mercurials are also used agriculturally as insecticides and fungicides.
Nickel
The toxicity of nickel to bacteria, yeasts, and fungi differs considerably.
Silver
The metabolism of bacteria is adversely affected by silver ions at concentrations of 0.01–0.1 mg/L. Therefore, even less soluble silver compounds, such as silver chloride, also act as bactericides or germicides, but not the much less soluble silver sulfide. In the presence of atmospheric oxygen, metallic silver also has a bactericidal effect due to the formation of silver oxide, which is soluble enough to cause it. Even objects with a solid silver surface (e.g., table silver, silver coins, or silver foil) have a bactericidal effect. Silver drinking vessels were carried by military commanders on expeditions for protection against disease. It was once common to place silver foil or even silver coins on wounds for the same reason.