It's about the biocidal effect of metals, especially heavy ones Razieh Mirsafaei

Discovered in 1893 by the Swiss botanist Karl Wilhelm von Nägeli, the oligodynamic effect refers to the toxic effect of metal ions on living organisms such as bacteria, algae and fungi. Copper, lead, zinc, gold and mercury can also furnish ions that will produce an antimicrobial effect, but the toxicity of lead and mercury preclude their use in this fashion. That wasn’t always the case. Mercury at one time was commonly used to treat syphilis, giving rise to the expression “A night with Venus, a lifetime with mercury.” However, because of mercury’s toxicity, that lifetime was often quite short. Copper and silver, on the other hand, have low toxicity by comparison and can be effectively used to battle bacteria. As early as the ancient dynasties of Egypt, silver coins were placed in the drinking vessels of the nobility to protect them from harm. Of course, this was not the result of any scientific investigation; the practice probably originated from some superstitious belief about the magical properties of precious metals. Over the years it became apparent that the silver coins really did have an effect: they kept water from becoming slimy. Storage of water in silver vessels was an obvious extension of this observation, affording the well-to-do some protection from waterborne diseases that were common before the introduction of chlorination. As recently as the twentieth century, when Maharaja Sawai Madho Singh II journeyed to Britain, he carried holy water from the Ganges River in two sterling silver vessels acclaimed to be the world’s largest silver containers. You do not have to be as rich as a maharaja to experience the oligodynamic effect of silver. The metal can be incorporated into urinary catheters and endotracheal breathing tubes to reduce infections, and fabrics can be formulated with small amounts of silver to control the bacteria responsible for churning out odorous compounds when they feast on sweat. The antimicrobial effect is actually due to silver ions—in other words, silver atoms that have lost an electron. These ions are produced whenever silver atoms at the surface of the metal react with either oxygen or hydrogen sulphide, the “rotten egg” compound that is always present in the air and water in trace amounts. Indeed the tarnish on silver is silver sulphide, the product of the reaction between silver and hydrogen sulphide. Silver ions inactivate enzymes that are essential for bacterial life. That’s why bacteria are killed when contaminated water is stored in a silver container. But in this case, the extent of disinfection is unreliable because the concentration of silver ions in the water cannot be controlled. The purity of the silver, the size of the container, whether the water is shaken—all are important determinants of the concentration of silver ions. However, techniques have been worked out to produce just the right concentration of ions by immersing a pair of silver electrodes connected to a direct current into water that needs to be purified. This was the method used to produce drinking water aboard the Apollo space flights and is used in hospital plumbing systems to deactivate legionella bacteria. Copper is often alloyed with silver in the electrodes to take advantage of its oligodynamic effect as well. Swimming pool disinfection systems using copper-silver ionization that allow for reduced use of chlorine are also available. If silver ions produced on the surface of the metal are the active disinfecting agent, it stands to reason that the surface area of the silver would play an important role in the effectiveness of the treatment. And it does. Particles of silver that are less than a billionth of a metre in size, commonly referred to as nanoparticles, have been shown to be especially effective at killing bacteria. A recent study by Dr. Derek Gray at McGill University showed that passing contaminated water through absorbent blotting paper treated with silver nanoparticles resulted in inactivation of bacteria. This has the earmarks of a landmark discovery, because the consumption of contaminated water in the developing world is a major health crisis. Nanosilver-impregnated paper is easy to produce and easy to use. Unfortunately, quackery often rides the coattails of science. And so it is in this case. Numerous websites promote the use of “colloidal silver” as a cure for cancer, diabetes, HIV infection and herpes. Colloids refer to a system in which finely divided particles are dispersed within a continuous medium without settling out. In the case of colloidal silver, these particles can be elemental silver or particles of silver compounds. Indeed, they may well have an antibacterial effect in a Petri dish, but that is a long way from having an antibacterial effect when taken internally. No scientific evidence supports the benefit of ingesting any form of colloidal silver. Making health claims on its behalf is illegal, but colloidal silver can be sold as a dietary supplement. That is a curiosity, because humans have no dietary requirement for silver and there is no such thing as silver deficiency. But there certainly is such a thing as silver excess. The metal can deposit in the skin as well as in internal organs, with the result being a condition known as argyria. Its hallmark is grey-blue skin, a condition that is irreversible. One of the most famous cases was that of the Blue Man who was a featured attraction in Barnum and Bailey’s circus in the early years of the twentieth century. He had apparently tried to cure his syphilis by ingesting silver nitrate, but succeeded only in making himself blue. More recently, Stan Jones, an American Libertarian who twice ran unsuccessfully for the U.S. Senate as well as for governor of Montana, did succeed in becoming blue. Back in 2000, he was worried that computers would stop functioning and that this would somehow make antibiotics unavailable. He decided to take preventative action and started to take a colloidal silver preparation he made himself by passing an electric current through a solution equipped with silver electrodes. Unfortunately, he didn’t know what he was doing and used too high a voltage, and his solution contained a great deal of silver. He turned blue. But he is not singing the blues, maintaining that he is healthy. He still dopes himself with colloidal silver. Pretty dopey, actually.

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