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THE HARD SCIENCE
BEHIND WHY COPPER WORKS
COPPER and COPPER ALLOYS as ANTIMICROBIALS
Many Metals Cause Death of Microbes (Mercury, Silver, Bismuth, Copper….). Copper is unique. In its solid form, it is an effective antimicrobial in reasonable time frames while being physically inert to mammals. It is an essential micronutrient (United States Recommended Daily Allowance of 0.9 mg/day) ingested as copper ions as part of a normal diet or supplement. In its un-ionized solid forms, copper is durable and wear resistant. As such, it can be formed into various useful configurations while maintaining its antimicrobial properties.
While our ancestors may not have related “antimicrobial” activity to their use of copper, they realized that water held or carried in buckets made of copper or copper alloys was not slimy when compared to water held or carried in buckets made of wood. Copper piping provided water of greater clarity and less odor than many other piping materials. And copper has been/is used in roof construction or placed in strips at the higher level rows of roofing shingles to reduce or eliminate mold growth on the roofs. Copper is also used, particularly in brass form, to prevent bio-marine fouling.
Examples of Microbes Killed by Solid Copper or Copper Alloys:
- Enterobacter aerogenes
- Staphylococcus aureus
- Pseudomonas Aerugnosa
- Drug Resistant Staphylococcus aureus
- Clostridium difficile
- Influenza A virus
Effectiveness of Microbial Kill with Solid Copper
The results of the 216 GLP tests, involving three test protocols, two to three lots of six different alloys, and six bacteria*, are summarized in Table 1. In both the Efficacy as a Sanitizer test and Residual Self-Sanitizing test (wear test), a reduction in live bacteria greater than 99.9% is seen in all seventy two tests when compared to S304. In the Continuous Reduction of Bacterial Contaminants test, a reduction of greater than 99.9% is found in sixty-three out of the seventy-two tests, again when compared to S304. In the remaining nine tests, reductions ranged from 99.3% to 99.9%. In summary, a reduction greater than 99.9% was seen on 207 out of 216 tests.
The reduction seen in the remaining nine tests ranged from 99.3% to 99.9%. These results indicate that the antimicrobial response of copper alloys is effective, enduring and reproducible.
Table 1: Average Percent Reduction of Bacterial Contamination (Good Laboratory Practice Studies) NOTE: 60% copper content was the lower limit of testing.
Continuous Kill Effect of Copper on Microbes
Figure 2: Continuous Reduction test results for MRSA on copper alloy C11000 and stainless steel S30400. Each inoculation adds 650,000 CFUs.
OBSERVATION: This shows the self regenerative antimicrobial power of the copper surface. If someone uses it on their hands, then puts it in their pocket, the surface will be microbe free in a very short time.
Dry Kill of Microbes vs Wet Kill of Microbes on Copper
Recent studies showed that large amounts of copper ions were taken up by E. coli over 90 min, when cells were applied to copper coupons in a standing drop. When cells were plated on copper by the dry method, the accumulation of copper ions by cells was even more dramatic, reaching a low molar concentration, or 27-fold the level observed by wet plating, in a fraction of the time. The copper ion level of cells remained high throughout the killing phase, suggesting that cells become overwhelmed by their intracellular copper.
Espírito Santo C, Lam EW, Elowsky CG, Quaranta D, Domaille DW, Chang CJ, Grass GAppl Environ Microbiol. 2011 Feb; 77(3):794-802.
Kill Rate of Microbes Versus Temperature
NOTE that the kill time decreases by 1/3 going from 4 °C (39 °F) to 20 °C (68 °F). Going to 37 °C (98.6 °F) should decrease by 1/3 again, but a reference to research at body temperature has not been found.
Results of E. coli O157:H7 destruction on an alloy containing 99.9% copper (C11000) demonstrate that this pathogen is rapidly and almost completely killed (over 99.9% kill rate) within ninety minutes at room temperature (20 °C). At chill temperatures (4 °C), over 99.9% of E. coli O157:H7 are killed within 270 minutes. E. coli O157:H7 destruction on several copper alloys containing 99%–100% copper (including C10200, C11000, C18080, and C19700) at room temperature begins within minutes. At chilled temperatures, the inactivation process takes about an hour longer. No significant reduction in the amount of viable E. coli O157:H7 occurs on stainless steel after 270 minutes.
Wilks, SA; Michels, H; Keevil, CW (2005). “The survival of Escherichia coli O157 on a range of metal surfaces”. International Journal of Food Microbiology PMID 16253366 doi10.1016/j.ijfoodmicro.2005.04.021
Michels, H. T.; Wilks, S. A.; Noyce, J. O.; Keevil, C. W. 2005, Copper Alloys for Human Infectious Disease Control, Presented at Materials Science and Technology Conference, September 25–28, 2005, Pittsburgh, PA; Copper for the 21st Century Symposium.
Other Information on the Kill Effects of Solid Copper/Copper Alloys The study of the antimicrobial properties of metallic copper surfaces is a relatively recent development and gained momentum when the Environmental Protection Agency (EPA) registered almost 300 different copper surfaces as antimicrobial in 2008.
( http://www.epa.gov/pesticides/factsheets/copper-alloy-products.htm). https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3067274/ )
For the most part, the bacterial kill rate of copper alloys increased with increasing copper content of the alloy. This is further evidence of copper’s intrinsic antibacterial properties.
Michels, H. T.; Wilks, S. A.; Keevil, C. W. 2004, “Effects of Copper Alloy Surfaces on the Viability of Bacterium, E. coli 0157:H7″, The Second Global Congress Dedicated to Hygienic Coatings & Surface Conference Papers, Orlando, Florida, US, 26–28 January 2004, Paper 16, Paint Research Association, Middlesex, UK
Michels, H. T.; Wilks, S. A.; Keevil, C. W. (2003), The Antimicrobial Effects of Copper Alloy Surfaces on the Bacterium E. coli O157:H7, Proceedings of Copper 2003 – Cobre 2003, The 5th International Conference, Santiago, Chile, Vol. 1 – Plenary Lectures, Economics and Applications of Copper, pp. 439–450, The Canadian Institute of Mining, Metallurgy and Petroleum, Montreal, Quebec, Canada, (presented in Santiago, Chile, November 30–December 3, 2003)
Updated Draft Protocol for the Evaluation of Bactericidal Activity of Hard, Non-porous Copper Containing Surface Products issued on 1/29/2016. Amongst the requirements listed is “An effective product is expected to achieve a 3 log10 reduction (LR) in viable bacteria (compared to the stainless steel control) for each microbe within a 1 hr contact period.”
It should also be noted that solid copper used in a manner to stimulate rubbing a copper device in one’s hands in Vitro-Skin tests on Staphylococcus aureus and Escherichia coli at Accuratus labs confirmed organism kill. In the case of the 3 minute test where the copper was rubbed very lightly on the inoculated Vitro-Skin, the kill was 81 to 86%. For the 1 minute test wherein the rubbing action better replicated the rubbing action of a piece of copper (per agreement of the testing parties after observing hand rubbing) in one’s hands, the kill was 94%.
Other Testing And Results
NON-GLP STUDY REPORT
Ex-Vivo Antibacterial Evaluation of Topical Products Using a Vitro-Skin® Model
PRODUCT IDENTITY: C-220 Copper Sheet 0.050″ Thickness
AUTHOR – Matthew Sathe, B.S. Senior Microbiologist
STUDY COMPLETION DATE
October 27, 2017
Accuratus Lab Services
1285 Corporate Center Drive, Suite 110
Eagan, MN 55121
General Study Information
|Study Title:||Ex-Vivo Antibacterial Evaluation of Topical Products Using a Vitro-Skin® Model|
|Protocol Number:||BOV002100917. EXVO|
Test Substance Identity
|Test Substance Name:||C-220 Copper Sheet 0.050″ thickness|
|Date Sample Received:||October 11, 2017|
|Study Initation Date:||October 18, 2017|
|Experimental Start Date:||October 24, 2017|
|Experimental End Date:||October 26, 2017|
|Study Completion Date:||October 27, 2017|
The test organisms used in this study were obtained from the American Type Culture Collection (ATCC) Manassas, Va.
|Test Substance Preparation:||Ready to Use (RTU) copper bar|
|Test Exposure Time:||1 minute (rubbing the bar on the inoculated and dried Vitro-Skin®)|
|Exposure Temperature:||Ambient (20° C with 28% relative humidity)|
|Number of Carriers Tested:||2 tests and 2 control carriers|
|Organic Soil Load:||none|
|Neutralizer:||Letheen Broth (20 ml)|
|Agar Plate Medium:||Tryptic Soy Agar with 5% Sheep Blood|
A film of the test organism dried onto a 1″ x 1″ demarcated area of 1.5″ x 1.5″ rehydrated Vitro-Skin® carriers was treated by rubbing the copper bar test material in circles, with light to medium pressure, over the inoculated surface for the exposure time. Following exposure, each carrier was neutralized and assayed for survivors. Appropriate culture purity, neutralizer sterility, carrier sterility and population controls were performed. Percent and Log10 reductions were determined for the test based on the test population control results.
Per Sponsor’s direction, the study was not required to be conducted under U.S. EPA 40 CFR Part 160 or U.S. FDA 21 CFR Part 58.
Table 2: Population Control Results
CFU = Colony Forming Unit
Table 3: Test Results Against
Staphylococcus aureus (ATCC6538)
CFU = Colony Forming Unit
T = Too Numerous To Count (>300)
The control results for culture purity, neutralizer sterility and carrier sterility were all acceptable.
C-220 Copper Sheet 0.050″ Thickness, ready to use, demonstrated a 94.0% (1.22 10910) reduction of Staphylococcus aureus (ATCC 6538) following a 1 minute rubbing exposure time at ambient temperature (20° C).