Silver

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Silver is a naturally occurring metal. In the Periodic Table its symbol is Ag. In the environment, silver often combines with other elements such as sulfide, chloride, and nitrate.[1] Whereas pure silver is silver (in color), silver nitrate and silver chloride are powdery white and silver sulfide and silver oxide are dark grey to black. While silver is found in silver mines, it is also found as a by-product from mining copper, lead, zinc, and gold ores.[2] Silver is highly toxic to aquatic organisms. It is persistent in the environment and it can bioaccumulate in some organisms, such as clams.[3] The U.S. EPA recommends limiting silver in drinking water to a concentration of 0.10 milligrams per liter of water (0.10 mg/L or about 1 part per million).[4] However, this regulation is a "secondary" guideline, making it non-enforceable (although individual states may choose to enforce it).

Uses

Silver is used in jewelry, silverware, electronic equipment, dental fillings, and in lozonges and chewing gums that help people stop smoking. Additionally, it is used to make photographs, in brazing alloys and solders, to disinfect drinking water and water in swimming pools, and as an antibacterial agent.[5]

Nanosilver, tiny particles of silver that range from 1 to 100 nanometers in diameter, is used for its antimicrobial properties in hospitals and consumer products. As of 2007, more than 500 consumer products contained some form of engineered nanoparticles.[6] About 20 percent of the 500 contained nanosilver. Products containing nanosilver include socks, paints, bandages, and food containers. In clothing, nanosilver is used to restrict the growth of odor-causing bacteria.

Silver in the Environment

Silver can be released into the air and water through natural processes, such as the weathering of rocks.[7] Humans also release silver into the air by processing ores, manufacturing cement, and burning fossil fuels. Photographic processing can release it into the water. Increased use of silver as a pesticide in household products may lead to increased silver pollution in the environment.

Silver in Effluent and Sewage Sludge

In the Targeted National Sewage Sludge Survey, a 2009 test of 84 samples of sewage sludge from around the U.S., the EPA found silver in every sample in concentrations ranging from 1.94 to 856 parts per million.[8]

In comments to the EPA, officials from the sewage industry expressed concern about the increased use of silver, particularly nanosilver, as a pesticide in household products.[9] The comments note that when the wastewater treatment plant is successful at removing silver from wastewater, all that does is remove the silver from the effluent only to put it into sewage sludge. The sewage industry worries that high concentrations of silver in sewage sludge will make them unable to dispose of sludge via land application. The letter says: "Widespread use of household products that release silver ions into sanitary sewer systems could increase silver concentrations in POTW influents, effluents, and biosolids. If silver pesticide product use becomes common, wastewater silver discharges could reach levels not seen in the last two decades—and could have adverse impacts on our wastewater treatment process as well as on the quality of our effluent and biosolids." The letter goes on to note that most silver used in products will ultimately make its way to wastewater treatment facilities, as it does not biodegrade.

They add that "two related studies, Choi and Hu (2008)[10] and Choi et al. (2008)[11] found that silver particles less than 5 nanometers in diameter are uniquely toxic to nitrifying bacteria, which are critical to biological nutrient removal at POTWs." Furthermore, they note that particle size impacts silver's toxicity to aquatic organisms and that wastewater treatment plants may not be able to remove silver from wastewater if the particles are very small.

Human Exposure and Health Effects

Humans are exposed to silver by breathing low levels in the air, swallowing it in food or drinking water, using anti-smoking lozenges or gums that contain silver, or working with silver while making jewelry, soldering, or working on photography.[12]

The most common human health effect from exposure to high levels of silver over a long period of time is a condition called arygria in which skin and other body tissues turn blue-gray in color.[13] Argyria is a permanent effect, but it is believed to be only a cosmetic problem and not harmful. Many believe that argyria is the origin of the term "blue blood" to denote aristocrats, as the rich could afford to eat from silver utensils and take medicines containing silver.

If exposed to high levels of silver in the air, humans may develop breathing problems, lung and throat irritation, and stomach pains.[14] Additionally, those who are allergic to silver may develop rashes, swelling, and inflammation from skin contact.[15]

Articles and resources

Related SourceWatch articles

References

  1. ToxFAQs for Silver, Agency for Toxic Substances and Disease Registry, Accessed August 24, 2010.
  2. ToxFAQs for Silver, Agency for Toxic Substances and Disease Registry, Accessed August 24, 2010.
  3. Ben Horenstein, Silver and Compounds Registration Review (Docket Number EPA–HQ–OPP–2009–0334), Tri-TAC, East Bay Municipal Utility District, September 9, 2009
  4. U.S., EPA, National Secondary Drinking Water Regulations, Accessed August 24, 2010.
  5. ToxFAQs for Silver, Agency for Toxic Substances and Disease Registry, Accessed August 24, 2010.
  6. Troy M. Benn and Paul Westerhoff, "Nanoparticle Silver Released into Water from Commercially Available Sock Fabrics", Environmental Science & Technology, 2008.
  7. ToxFAQs for Silver, Agency for Toxic Substances and Disease Registry, Accessed August 24, 2010.
  8. Targeted National Sewage Sludge Survey Report, US EPA website, Accessed August 28, 2010.
  9. Ben Horenstein, Silver and Compounds Registration Review (Docket Number EPA–HQ–OPP–2009–0334), Tri-TAC, East Bay Municipal Utility District, September 9, 2009
  10. Choi, O. and Z. Hu (2008). "Size dependent and reactive oxygen species related nanosilver toxicity to nitrifying bacteria." Environmental Science & Technology 42(12): 4583-8
  11. Choi, O., K. K. Deng, et al. (2008). “The inhibitory effects of silver nanoparticles, silver ions, and silver chloride colloids on microbial growth.” Water Research 42: 2066-2074.
  12. ToxFAQs for Silver, Agency for Toxic Substances and Disease Registry, Accessed August 24, 2010.
  13. ToxFAQs for Silver, Agency for Toxic Substances and Disease Registry, Accessed August 24, 2010.
  14. ToxFAQs for Silver, Agency for Toxic Substances and Disease Registry, Accessed August 24, 2010.
  15. ToxFAQs for Silver, Agency for Toxic Substances and Disease Registry, Accessed August 24, 2010.

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