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Medical Devices and Hygiene Products
The Safety of Silver
Silver is a substance that is highly safe for the human body.
Silver was used in ancient times for tableware and chopsticks, and in modern times it is used in urinary disinfectants, nasal preparations, eye drops, etc. When taken orally, it is used as an intestinal disinfectant, and silver colloids are used intravenously as an anti-infective drug. Silver compounds have been used medically for centuries to treat various diseases, and in normal clinical practice there is little evidence of toxicity and they are not carcinogenic.
Argyria can occur in some cases when silver compounds or drugs containing silver are used for medical purposes. However, in studies of argyria, the incidence was low even after 30 to 40 intravenous injections of 0.9 to 1.5 g of silver over a period of 2 to 3 years. Argyria is a marked pigmentation of the skin, turning it gray-blue, but is not thought to be associated with any other health problems.
History of silver ion antibacterial properties and its application to water treatment
Even at very low concentrations, silver solutions have the effect of suppressing microorganisms in water. Around 100 years ago (1893), a Swiss scientist named Nagerly discovered that extremely small amounts of certain metal salts have the effect of killing algae, and around 1932, it was confirmed that extremely small amounts of metal ions act on the cells of living organisms. In 1933, a German scientist named Klaus devised a device to apply silver ions to drinking water, and research on metal ions was also conducted in Japan before the war, with the Faculty of Medicine of Tokyo Imperial University publishing a paper titled "Study on the effects of metals and metal ions on microorganisms."
In 1952, the American Chemical Society held a subcommittee meeting on "Water, Wastewater, and Sanitation Chemistry" in Atlanta, USA, where a paper on "Water Disinfection with Silver" was published. As mentioned above, silver ions have been used for water treatment for a long time, and we can see that silver ions are a highly safe substance.
Are all metal ions harmful?
It is natural to worry that something that kills bacteria might have a negative effect on the human body, but silver (chemical symbol Ag) is actually a very classic substance, and is so safe that it is used not only as an antibacterial agent, but even as a food additive. For example, silver (Ag) is used in the silver-colored granular alaxan used in decorated cakes, and in the silver surface of the traditional cooling agent, Jintan.
Also, many homes are now installing water purifiers, and silver is often used for the antibacterial properties inside (if the purifier does not have antibacterial properties, bacteria will grow inside the purifier), and in Europe it is also used to directly disinfect drinking water. In Japan, the water quality standards of the Water Supply Act determine index values for metal ions that may be contained in drinking water and are recognized as harmful, but there is no index value for silver. In Canada, the initial regulatory value was 0.05 mg/l, but silver was removed from the drinking water quality guidelines in 1989.
The US Environmental Protection Agency (USEPA) drinking water regulations do not specify silver in the primary standard (NPDWRs, standards that must be followed for tap water), and only have a secondary standard (NSDWRs, recommended standards that do not necessarily have to be followed) with a regulation value of 0.1 mg/l. The World Health Organization (WHO) also states that silver compounds are not carcinogenic, and that there is no effect on the human body from acute or chronic exposure, and that even exposure to water containing 0.1 mg/l silver for 70 years does not meet the NOAEL (maximum amount not considered harmful). (If you drink 2 liters of water containing 0.1 mg/l silver every day for 70 years, that's half the NOAEL.)
＜reference＞USEPA websitehttps://www.epa.gov/OST/pc/drinking.html