Silver as a Contaminant in Water
Biologically, silver is a nonessential, non-beneficial element to humans. There are no scientific
studies to show adverse health due to its presence in drinking water from natural sources. However,
because of its bactericidal abilities, silver is used as a water bacteriostat in carbon containing water
filters. The silver is deposited onto the carbon granules to inhibit the growth of bacteria on the surfaces
of these carbon particles. Such filters tend to leach out trace levels of silver into the effluent water. At
anticipated concentrations, the ingestion of silver has no documented detrimental effect on humans.
Sources of Contaminant:
In soil as insoluble silver chloride (AgCl) and silver sulfide (Ag2S)
Majority from use as a bacteriostat in water treatment devices
Potential Health Effects:
Argyria – discoloration of skin, hair, and various organs
Strong acid cation exchange (Na+)
When ingested and absorbed, silver is held indefinitely within tissue, particularly skin, eyes, and
mucous membranes. Skin discoloration is a cosmetic effect related to silver ingestion. This effect,
called argyria, does not impair body function.
The U.S. Environmental Protection Agency has set a non-enforceable secondary standard for silver
because of its ability to cause aesthetic discolorations of the skin or argyria. This mirrors the World
Health Organization set a guideline also at 0.1mg/L over a lifetime of exposure in drinking water. The
Secondary Maximum Contaminant Level (SMCL) for silver is 0.10 (milligrams per liter) mg/L.
Devices based on strong acid cation exchange, reverse osmosis and
distillation either as POU or POE devices.
Since silver is a non-enforceable secondary drinking water
contaminant, it is rarely treated at the Municipal level.
Current technology suggests that several techniques may be used for removing the silver ion from
drinking water including reverse osmosis, distillation, and cation exchange.
Reverse osmosis is capable of reducing the silver cation concentration by up to 90 percent of the
influent water levels.
Distillation is capable of reducing the silver concentration by greater than 98 percent.
The treatment methods listed herein are generally recognized as techniques that can effectively
reduce the listed contaminants sufficiently to meet or exceed the relevant MCL.
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