Properties of Copper (Cu)

Copper As A Biocidal Tool –

Abstract: Copper ions, either alone or in copper complexes, have been used to disinfect liquids, solids and human tissuefor centuries. Today copper is used as a water purifier, algaecide, fungicide, nematocide, molluscicide as well as an anti-bacterial and anti-fouling agent. Copper also displays potent anti-viral activity.

Mechanisms of antimicrobial action

The oligodynamic effect was discovered in 1893 as a toxic effect of metal ions on living cells, algae, molds, spores, fungi, viruses, prokaryotic, and eukaryotic microorganisms, even in relatively low concentrations. This antimicrobial effect is shown by ions of copper as well as mercury, silver, iron, lead, zinc, bismuth, gold, and aluminium.

In 1973, researchers at Battelle Columbus Laboratories conducted a comprehensive literature, technology and patent search that traced the history of understanding the “bacteriostatic and sanitizing properties of copper and copper alloy surfaces”, which demonstrated that copper, in very small quantities, has the power to control a wide range of molds, fungi, algae and harmful microbes. Of the 312 citations mentioned in the review across the time period 1892–1973, the observations below are noteworthy:

Copper inhibits Actinomucor elegans, Aspergillus niger, Bacterium linens, Bacillus megaterium, Bacillus subtilis, Brevibacterium erythrogenes, Candida utilis, Penicillium chrysogenum, Rhizopus niveus, Saccharomyces mandshuricus, and Saccharomyces cerevisiae in concentrations above 10 g/L.
Candida utilis (formerly, Torulopsis utilis) is completely inhibited at 0.04 g/L copper concentrations.
Tubercle bacillus is inhibited by copper as simple cations or complex anions in concentrations from 0.02 to 0.2 g/L.
Achromobacter fischeri and Photobacterium phosphoreum growth is inhibited by metallic copper.
Paramecium caudatum cell division is reduced by copper plates placed on Petri dish covers containing infusoria and nutrient media.
Poliovirus is inactivated within 10 minutes of exposure to copper with ascorbic acid.

A subsequent paper probed some of copper’s antimicrobial mechanisms and cited no fewer than 120 investigations into the efficacy of copper’s action on microbes. The authors noted that the antimicrobial mechanisms are very complex and take place in many ways, both inside cells and in the interstitial spaces between cells.

Examples of some of the molecular mechanisms noted by various researchers include the following:

The 3-dimensional structure of proteins can be altered by copper, so that the proteins can no longer perform their normal functions. The result is inactivation of bacteria or viruses
Copper complexes form radicals that inactivate viruses.
Copper may disrupt enzyme structures, and functions by binding to sulfur- or carboxylate-containing groups and amino groups of proteins.
Copper may interfere with other essential elements, such as zinc and iron.
Copper facilitates deleterious activity in superoxide radicals. Repeated redox reactions on site-specific macromolecules generate HO• radicals, thereby causing “multiple hit damage” at target sites.
Copper can interact with lipids, causing their peroxidation and opening holes in the cell membranes, thereby compromising the integrity of cells. This can cause leakage of essential solutes, which in turn, can have a desiccating effect.
Copper damages the respiratory chain in Escherichia coli cells. and is associated with impaired cellular metabolism.
Faster corrosion correlates with faster inactivation of microorganisms. This may be due to increased availability of cupric ion, Cu2+, which is believed to be responsible for the antimicrobial action.
In inactivation experiments on the flu strain, H1N1, which is nearly identical to the H5N1 avian strain and the 2009 H1N1 (swine flu) strain, researchers hypothesized that copper’s antimicrobial action probably attacks the overall structure of the virus and therefore has a broad-spectrum effect.
Microbes require copper-containing enzymes to drive certain vital chemical reactions. Excess copper, however, can affect proteins and enzymes in microbes, thereby inhibiting their activities. Researchers believe that excess copper has the potential to disrupt cell function both inside cells and in the interstitial spaces between cells, probably acting on the cells’ outer envelope.

Currently, researchers believe that the most important antimicrobial mechanisms for copper are as follows:

Elevated copper levels inside a cell causes oxidative stress and the generation of hydrogen peroxide. Under these conditions, copper participates in the so-called Fenton-type reaction — a chemical reaction causing oxidative damage to cells.
Excess copper causes a decline in the membrane integrity of microbes, leading to leakage of specific essential cell nutrients, such as potassium and glutamate. This leads to desiccation and subsequent cell death.
While copper is needed for many protein functions, in an excess situation (as on a copper alloy surface), copper binds to proteins that do not require copper for their function. This “inappropriate” binding leads to loss-of-function of the protein, and/or breakdown of the protein into nonfunctional portions.

These potential mechanisms, as well as others, are the subject of continuing study by academic research laboratories around the world.