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Sunday, October 20, 2013

Disinfectant Chemistry Report Card #17 - Silver and Copper as Antimicrobial Surface Agents

Copper is the oldest metal known to human civilization, and dates back to about 10,000 years. Silver mining also started about 5,000 years ago, where silver was used as a value resource and coinage. Antimicrobial effects of both metals have been utilized long before the concept of microbes became reality. Containers with an external layer of silver or copper were used to keep water fresh and food from spoiling. Silver coins were also dropped into milk containers to prevent milk from spoiling quickly. Direct use of copper and silver as antimicrobials started only in the recent decades. Disinfectant solutions containing colloidal copper or silver ions are used to treat hard surfaces. An external layer of copper is used on certain high-touch surfaces in healthcare settings to aid in prevention of microbial cross-contamination. Certain soft surfaces, such as fabrics, are also impregnated with silver nanoparticles to control and minimize the growth of odor causing bacteria. 

Based on the chemical properties of silver or copper ions in solution, such disinfectants by themselves would have no cleaning power, unless additional surfactants and soaps are added to the formulation. In general, both metal ions are cytotoxic to pathogenic bacteria. Free silver ions disrupt the functional properties of active proteins such as enzymes. This change would cause alteration of the 3D structure of proteins and therefore result in loss of function. Silver is also hypothesized to damage DNA structures. Copper is known to interact with active proteins in microbial cells and therefore interrupt their functions, resulting in microbial death. Copper ions are also thought to interact with membrane lipids which results in rupturing of the microbial cells.

These metal ions can in additionally affect viruses, as viruses also have protein and lipid structures on their external shell. Resistant strains of pathogens have been known to combat against the metal ions by either preventing their entry into the cell, or through mutations that result in change of their protein surfaces.

Silver oxidation does occur slowly. Disinfectant solutions containing colloidal silver care exposed to gradual oxidation, which would eventually cause them to crash out of the solution and precipitate. Once out of solution, they no longer are available to interact with microbial cells. Antimicrobial surfaces covered with copper coatings also undergo oxidation. Such antimicrobial hard surfaces are in fact affected by oxidation and deposition of organic soils on the most surface layer of copper. Organic soils and oxidized ions can act as a barrier layer and prevent the surface microbes from touching and interacting with the silver or copper layers. Therefore, the surfaces have to be cleaned and kept residue free in order to be effective against pathogens. Copper and silver coated surfaces also impose compatibility problems when they are to be disinfected with various cleaner disinfectant agents. Such incompatibilities may arise in forms of corrosion, or immediate formation of an oxidized film layer that either degrades the surface or decreases the efficacy of those against pathogens.

Continuous exposure of humans to solutions with colloidal silver can result in deposition of silver particles inside the skin cells. Over a very long exposure time and over-accumulation, it can cause a condition called Argyria, which is discolouration of skin into a blue-gray colour.

Both copper and silver, especially silver, are extremely harmful to the environment. Silver is known to have high aquatic toxicity as it can bioaccumulate in marine organisms’ tissues. Therefore, proper disposal of disinfectants containing colloidal silver or copper are often problematic, as the intent is to prevent its flow to open waters and oceans.

Here’s how we would score Silver and Copper on the key decision making criteria for antimicrobial surface agents:

Speed of Disinfection – N/A

o Use of Silver and Copper provides continuous reduction and inhibits growth of pathogens on surfaces (e.g. over extended periods of time from 2 - 24hrs)

Spectrum of Kill – C

o Efficacy against bacteria and viruses has been shown but is dependent upon the metal ions being able to directly contact the pathogen

Safety Profile – B - C

o Prolonged to silver can lead to bio-accumulation on skin and lead to health concerns

Environmental Profile – D

o Both copper and silver and known to be extremely harmful to the environment

o Silver in particular has high aquatic toxicity and can bioaccumulate in tissues

Cost Effectiveness – D

o Such products are still in their infancy, facilities need to weigh the cost of use versus benefit to infection reduction


**For more in-depth scientific information about Silver, Copper and other Antimicrobial Surface Agents, stay tuned to www.infectionpreventionresource.com.
Bugging Off!




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