Edcuation
root *arg- for "grey" or "shining")
Silver is a naturally occurring metal with a soft, white, lustrous appearance and is also known by the chemical symbol Ag and atomic number 47. Silver has been used for thousands of years in jewelry, coinage and ornaments and its anti-bacterial properties were known even to the ancient Greeks. In modern times, silver is still widely used and valued in much the same way however it’s now employed in a large range of industrial and technological applications.
To learn more about silver, its uses and history click the links below. Click again to close the selection:
- Does silver cause bacteria resistance?
- The risk of bacteria developing resistance to silver is low.
- Silver ions (Ag+) kill bacteria via 3 separate mechanisms [1]. It is unlikely that bacteria can develop resistance against all 3 mechanisms [2].
- Some bacteria strains have shown the theoretical ability to develop resistance to silver however it is metabolically expensive making it difficult to compete against nonresistant bacteria and they do not persist through subsequent generations [3].
- Silver materials have been in common use in hospitals for decades [3].
- The scientific literature recognizes that the risk of resistance to silver is low and this is also corroborated by historical data in hospitals and modern targeted studies [4, 5].
- The ability of bacteria to develop silver resistance is understood to be a very low risk compared to the ability of bacteria to resist antibiotics [6]. Indeed, Percival and co-workers state that “it is important to note that bacteria have been exposed to subinhibitory levels of Ag+ for over four billion years and no widespread resistance has been evident to date, whereas widespread antibiotic resistance has developed within the last 60 years.” [7]
- There is no direct evidence that silver resistance mechanisms confer cross-resistance to antibiotics [3].
Notes
[1] I.Sondi, B.Salopek-Sondi, "Silver nanoparticles as antimicrobial agent: a case study of E. coli as a model for gram-negative bacteria", Journal of Colloid and Interface Science, 275 (2004) 177–182. http://dx.doi.org/10.1016/j.jcis.2004.02.012
[2] V.Edwards-Jones, “The benefits of silver in hygiene, personal care and healthcare”, Letters in Applied Microbiology, 49 (2009) 147-152. http://dx.doi.org/10.1111/j.1472-765X.2009.02648.x
[3] I.Chopra, “The increasing use of silver-based products as antimicrobial agents: a useful development or a cause for concern?”, Journal of Antimicrobial Chemotherapy, 59 (2007) 587-590. http://dx.doi.org/10.1093/jac/dkm224
[4] SL.Percival, E.Woods, M.Nutekpor, P.Bowler, A.Radford, C.Cochrane, “Prevalence of silver resistance in bacteria isolated from diabetic foot ulcers and efficacy of silver-containing wound dressings”, Ostomy Wound Management, 54(3) (2008) 30-40. http://www.ncbi.nlm.nih.gov/pubmed/18382046
[5] JV.Loh, SL.Percival, EJ.Woods, NJ.Williams, CA.Cochrane, “Silver resistance in MRSA isolated from wound and nasal sources in humans and animals”, International Wound Journal, 6(1) (2008) 32-38. http://dx.doi.org/10.1111/j.1742-481X.2008.00563.x
[6] M.Rai, A.Yadav, A.Gade, “Silver nanoparticles as a new generation of antimicrobials”, Biotechnology Advances, 27 (2009) 76-83. http://dx.doi.org/10.1016/j.biotechadv.2008.09.002
[7] SL.Percival, PG.Bowler, D. Russell, “Bacterial resistance to silver in wound care”, Journal of Hospital Infection, 60(1) (2005) 1-7. http://dx.doi.org/10.1016/j.jhin.2004.11.014
- Does silver negatively impact wastewater treatment plants?
- Municipal waste water (sewerage) treatment plants rely on the action of bacteria for the effective treatment of the waste.
- Silver is effectively removed from water in standard wastewater treatment plants[1].
- Silver ions (Ag+) complex easily with common waste components such as chloride, sulphide and thiosulfite as well as organic carbon. Suspended solid particulate material also effectively binds silver, removing it from the wastewater.
- The established state of scientific knowledge is that the environmental passivation of silver ions is very effective and silver in wastewater has minimal impact on the biological viability of the treatment plant sludge [2, 3, 4].
- The latest research shows that silver and silver nanoparticles do not impact the viability of wastewater plants – a finding based on studies from lab-scale, pilot-plant scale through to large-scale municipal wastewater treatment systems [5, 6].
Notes
[1] Wang, J., Huang C.P., Pirestani, D."Interactions of silver with wastewater constituents" Water Research 37 (2003) 4444-4452. http://dx.doi.org/10.1016/S0043-1354(03)00407-X
[2] O.Choi, TE.Clevenger, B.Deng, RY.Surampalli, L.Ross, Z.Hu, “Role of sulfide and ligand strength in controlling nanosilver toxicity”, Water Research, 43 (2009) 1879-1886. http://dx.doi.org/10.1016/j.watres.2009.01.029
[3] OK.Choi, ZQ.Hu, “Nitrification inhibition by silver nanoparticles”, Water Science and Technology, 59(9) (2009) 1699-1702. http://dx.doi.org/10.2166/wst.2009.205
[4] SA.Blaser, M.Scheringer, M.MacLeod, K.Hungerbühler, "Estimation of cumulative aquatic exposure and risk due to silver: Contribution of nano-functionalized plastics and textiles", Science of the Total Environment, 390 (2008) 396-409. http://dx.doi.org/10.1016/j.scitotenv.2007.10.010
[5] M.Burkhardt, S.Zuleeg, R.Kägi, B.Sinnet, J.Eugster, M.Boller, H.Siegrist,"Verhalten von Nanosilber in Kläranlagen und dessen Einfluss auf die Nitrifikationsleistung in Belebtschlamm", Umweltwiss Schadst Forsch, 22(5) (2010) 529-540. http://dx.doi.org/10.1007/s12302-010-0153-2
[6] B.Nowack,”Nanosilver revisited downstream”, Science, 330 (2010) 1054–1055. http://dx.doi.org/10.1126/science.1198074
- How does silver act as an antimicrobial?
- All silver-based antimicrobials act against bacteria through the action of silver ions (Ag+)
- The effect of silver ions against microorganisms is well established and is referred to as the oligodynamic effect [1]
- Silver ions interact with bacteria cells through 3 main mechanisms (see Figure):
- Damage bacteria cell membrane[2]
- Displace Ca2+ and Zn2+ ions[2]
- Interact with sulphur, oxygen or nitrogen[3]
- Silver ions are active against a broad range of gram-positive and gram-negative bacteria
- Unique qualities of silver ions (Ag+):
- Low risk for bacteria resistance [5]
- Effective in very low concentrations [4]
- No human toxicity
Notes
[1] U.S.EPA (1993). “EPA Re-registration Eligibility Document for Silver”, Case 4082, U.S. Environmental Protection Agency: http://www.epa.gov/oppsrrd1/REDs/old_reds/silver.pdf.
[2] I.Sondi, B.Salopek-Sondi,“Silver nanoparticles as antimicrobial agent: a case study on E. coli as a model for Gram-negative bacteria”, Journal of Colloid Interface Science, 275 (2004) 177-182. http://dx.doi.org/10.1016/j.jcis.2004.02.012
[3] Dowling DP, K.Donnelly, ML.McConnell, R.Eloy, MN.Arnaud,"Deposition of anti-bacterial silver coatings on polymeric substrates", Thin Solid Films, 398 (2001) 602-606. http://dx.doi.org/10.1016/S0040-6090(01)01326-8
[4] T.Gilchrist, DM.Healy, C.Drake,"Controlled silver-releasing polymers and their potential for urinary tract infection control", Biomaterials, 12 (1991) 76-78. http://www.ncbi.nlm.nih.gov/pubmed/2009349
[5] C.Damm, M.Neumann, H.Münstedt,"Properties of Nanosilver Coatings on Polymethyl Methacrylate", Soft materials, 3 (2006) 71-88. http://dx.doi.org/10.1080/15394450600766819
- What is Silver?
- Silver is a naturally occurring metal with a white shiny lustre.
- Silver is widely used throughout all aspects of society and industry.
- Silver has been used for ornaments and utensils for 5’000 years and as a precious metal, a monetary medium, and a basis for wealth for more than 2’000 years [1].
- Silver is most recognizable in jewelry, coins, mirrors, tableware and silverware.
- Silver also has numerous applications in medicine including the treatment of burn wounds and other ailments where the action of silver to protect against bacteria is well recognized.
- Silver is widely used throughout industry in applications ranging from electronic components, photography, electroplating of metals, solders, to catalysts used for production of industrial chemicals.
Notes
[1] WHO (2002). “Silver and Silver Compounds: Environmental Aspects”. Concise International Chemical Assessment Document 44, World Health Organization: http://www.inchem.org/documents/cicads/cicads/cicad44.htm.
- What is the ecotoxicity profile of silver?
- Ionic silver (Ag+) has potential for toxicity to aquatic organisms however in real-life exposure it is rapidly neutralised.
- Silver ions are extremely short lived in the environment due to the formation of silver sulfides which have no toxicity to bacteria or aquatic organisms [1]. Silver sulfide represents the final mineral fate of all silver.
- The toxic ionic form (Ag+) rapidly reverts to silver sulfide and is therefore present in extremely low concentrations under real environmental conditions [2].
- Even under conditions of heavy aquatic exposure, silver has a low risk of toxicity to aquatic organisms and humans [3, 4].
- A report by the World Health Organization states that “on the basis of available toxicity results it would be unlikely that bioavailable free silver ions would ever be at sufficiently high concentrations to cause toxicity in marine environments” [5].
- Latest research shows that silver ions and silver nanoparticles are rapidly converted to silver sulfide under environmental conditions [6, 7, 8].
Notes
[1] O.Choi, TE.Clevenger, B.Deng, RY.Surampalli, L.Ross, Z.Hu, “Role of sulfide and ligand strength in controlling nanosilver toxicity”, Water Research, 43 (2009) 1879-1886. http://dx.doi.org/10.1016/j.watres.2009.01.029
[2] O.Choi, KK.Deng, NJ.Kim, L.Ross, RY.Surampalli, Z.Hu, “The inhibitory effects of silver nanoparticles, silver ions, and silver chloride colloids on microbial growth”, Water Research, 42 (2008) 3066-3074. http://dx.doi.org/10.1016/j.watres.2008.02.021
[3] SA.Blaser, M.Scheringer, M.MacLeod, K.Hungerbühler, "Estimation of cumulative aquatic exposure and risk due to silver: Contribution of nano-functionalized plastics and textiles", Science of the Total Environment, 390 (2008) 396-409. http://dx.doi.org/10.1016/j.scitotenv.2007.10.010
[4] J.Warila, S.Batterman, DR.Passino-Reader, “A probabilistic model for silver bioaccumulation in aquatic systems and assessment of human health risks”, Environmental Toxicology and Chemistry, 20(2) (2001) 432-441. http://dx.doi.org/10.1002/etc.5620200226
[5] WHO (2002). “Silver and Silver Compounds: Environmental Aspects”. Concise International Chemical Assessment Document 44, World Health Organization: http://www.inchem.org/documents/cicads/cicads/cicad44.htm
[6] B.Kim, CS.Park, M.Murayama, MF.Hochella, “Discovery and Characterization of Silver Sulfide Nanoparticles in Final Sewage Sludge Products”, Environmental Science and Technology, 44 (2010) 7509–7514. http://dx.doi.org/10.1021/es101565j
[7] B.Nowack,”Nanosilver revisited downstream”, Science, 330 (2010) 1054–1055. http://dx.doi.org/10.1126/science.1198074
- What is the health and safety profile of silver?
- Silver is not toxic to humans and has no known carcinogenic or mutagenic potential [1].
- The most severe effect that silver is known to cause to humans is a cosmetic condition known as argyria – a grey discoloration of the skin which is not harmful to health [1]. The onset of argyria occurs only after ingesting large quantities of silver over a long period of time.
- Humans have been in safe contact with silver for many centuries.
Notes
[1] U.S.EPA (1993). “EPA Re-registration Eligibility Document for Silver”, Case 4082, U.S. Environmental Protection Agency: http://www.epa.gov/oppsrrd1/REDs/old_reds/silver.pdf.
- What is the natural level of silver in the environment?
- Silver is a naturally occurring substance
- Silver and minerals containing silver have been in contact with water from rainfall for millions of years and as such background levels of silver can be found in the environment.
- Typical environmental silver concentrations are as follows [1]:
Surface waters (lakes, rivers etc.) 0.2 – 2.0 ppb* Drinking ater (USA) up to 80 ppb Soil 0.2 – 0.3 ppb Notes
[1] U.S.PHS (1990). “Toxicological Profile for Silver”, Agency for Toxic Substances and Disease Registry U.S. Public Health Service: http://www.atsdr.cdc.gov/toxprofiles/tp146.pdf.
- Where does silver come from?
Minerals
- Silver minerals are found naturally in the earth
- Silver sulfides are the most common mineral composition (eg. argentite and acanthite)
- Silver metal can also be found in nature
Recycling
- Silver is readily recycled from scrap silver
Notes
[1] H.Renner etal., “Silver, Silver Compounds, and Silver Alloys” in Ullmann's Encylopedia of Industrial Chemistry, Wiley-VCH (2005).
- Why is silver used in textiles?
- Silver can be used as an antimicrobial treatment for textiles.
- Antimicrobial functionality brings value to textiles and consumers
- Preservative action (e.g. odor control, prevents discoloration etc.)
- Increased comfort
- Potential for water and energy savings through use lifetime (e.g wash at lower temperature, wash with less detergent, wash less frequently)
- Longer useful lifetime for articles
- Silver is not the only antimicrobial used in textiles -- there are many different antimicrobial agents available for textiles.
- Silver is the most sustainable choice. Silver can be used in significantly lower quantities than synthetic chemical biocides (eg. triclosan, quaternary ammonium).
Product type Silver Triclosan Quanternary ammonium
(Quats)Active ingredient Silver Chlorinated phenol e.g. Benzalkonium chloride Amount of active used on
textileLowest >10x higher than silver >100x higher than silver Raw materials Recycled Artificial Artificial Ecotoxicity?
(in real environmental
conditions)No Yes Yes Wastewater toxicity?
(in real environmental
conditions)No No Yes