Where are we on the copper-as-bacteria-killer story?
Well, more wikipedia research revealed that actually many other metals exhibit properties lethal to bacteria, fungi, and even small animals (think Arsenic as rat poison). I haven’t found a definitive answer to Why Copper? in terms of Why Not Other Metals? but have come up with a list of parameters likely to influence choosing the amber-colored metal over a metal like gold.
Factors Determining Selection of Metals for the Oligodynamic (aka, bacteria-killing) Effect:
— human health effects
— ease of working with it (there has to be a better word for that!)
— kind of interaction with bacteria cells
Price is a fairly obvious one, and human health effects likely drove the creation of Lululemon’s Silverescent line. (I’m kind of wishing for a rendition of Paul Simon’s “Diamonds on the Soles of Her Shoes” but instead, it’s “Silver in the Seams of Her Yoga Pants”). Ease of working with the metal is also quite obvious, especially if you think about the metals you are likely to find in nature, as metals, versus metals you are likely to find in nature as compounds (think sodium or calcium) as their elemental forms are unstable. From what I’ve read about the Oligodynamic Effect, it sounds like it’s merely the presence of positively charged ions that disrupt the proteins and other structures within a cell of a microorganism. Now, the very definition of “metal” is something that will lose electrons when it becomes an ion (as opposed to gain) and thus become positively charged. So I think in fact all metals would likely exhibit these murderous effects on microorganisms, to some degree, and the question on which one to harness becomes an interplay between an array of factors, including those listed above. The wikipedia article on the Oligodynamic Effect lists aluminum, antimony, arsenic, barium, bismuth (think pepto bismol and stomach bacteria!), boron, copper, gold, lead, mercury, nickel, silver, thallium, tin, and zinc as metals that exhibit this effect to some degree I get the feeling this is not a comprehensive list.
The other tricky bit here is that metals that are relatively cheap, easy to work with, and exhibit decent efficacy are likely the ones to be selected for continued research. Sounds like copper fits this bill. A 2009 study from the Nepal Journal of Science and Technology, entitled “Oligodynamic Action of Silver, Copper, and Brass on Enteric Bacteria Isolated from the Water of the Kathmandu Valley” tested the effects of water pots made from copper, silver, and brass (a copper and zinc alloy) on various drinking water-lurking bacteria such as Salmonella and E Coli. Copper showed the strongest effects on decreasing the bacterial population. The authors report that “complete inhibition of tested organisms was recorded within 4 to 48 hours of holding time.”
This fairly recent study also reports that while the exact mechanism of action of the oligodunamic effect is uncertain, there are a few knowns. Some data suggest that
— metal ions denature proteins of the target cells by binding to reactive parts of them
— copper ions distort cell walls by bonding to negatively charged groups and allowing silver ion into the cell (do they mean copper? this article has not-a-few typos)
On the doorknob front, a number of sources suggest avoiding aluminum and stainless steel doorknobs, which might as well be petri dishes for single-celled havoc-wreaking creatures. Instead, brass doorknobs essentially disinfect themselves within 7 hours. Anecdotally, a friend was telling me about the brass doorknobs at Penn Station. Great to know this is more than a cosmetic decision. (And makes me cringe at an acquaintance’s recent decision to eschew “all yellow metal” in his house. Ouch! Better stock up on some antibiotics!) In addition, this website recommends stripping the coating that makes brass doorknobs shiny for an even greater bactericidal effect.
As an especially exciting concluding note, a recent report shows that copper can kill MRSA. For those not familiar, MRSA is an especially frightening bacteria, an antibiotic-resistant Staphylococcus.
I’m not sure where I’m going to go with this. Write a longer, and more organized article on the oligodynamic effect? Write a story about it? Include it in a future novel? Time will tell. But for now I’m thinking my next trip is to the Home Depot for brass doorknobs.