You may or may not be aware of this, but silver nanoparticles (aka nanosilver) are special. They carry the beautiful “nanoparticle” buzzword, which means they must be special in some way (otherwise they would not be called nano) and they have antimicrobial properties. Nanosilver has been used in a vast array of consumer products to provide antimicrobial protection. This isn’t news. Silver salt (silver nitrate, actually) was used to help prevent and cure infections before the discovery of penicillin and is still used on burn victims. That’s one reason why some people drink colloidal silver (another word for a suspension of nanoparticles) as a dietary supplement.
But silver nanoparticles have not yet been proven to be safe for humans and the environment. There still are contradicting views in recent in vivo and in vitro studies involving silver nanoparticles. The most likely adverse effect of ingesting silver nanoparticles is a permanent cosmetic condition called argyria, in which a person’s body bioaccumulates silver in the dermis, giving it a blueish-grey hue. But when inhaled, silver nanoparticles, like most kinds of airborne particles, may deposit in the respiratory system and cause damage to the lungs and cardiovascular system.
Because we saw how many consumer products claiming to contain silver or silver nanoparticles were already available in the market, many of those catered to children, we decided to continue our quest for sustainable nanotechnology by studying the amount and type of silver (ionic or particulate) to which a child could become exposed while using these products in real-world situations.
We investigated the presence and release of silver in a number of products (plush toy, fabric products, breast milk storage bags, sippy cups, cleaning products, humidifiers, and humidifier accessory) into different biologically-relevant liquid media (water, orange juice, milk formula, sweat, urine, and saliva). We also let a few products sit outside, rubbed them into a concrete block, and exposed them to a UV lamp to promote aging to see if that affected the release of silver.
Our main results indicate that the release of silver from consumer products is very low (about 5% of silver present got released into liquid media in one of our scenarios) and is mainly driven by dissolution, which means that the consumer is more likely to be exposed to silver ions, not nanoparticles. We also found that the amount of silver that is released by products, and thus might be internalized by a consumer, heavily depends on the biological media involved. Sweat, because it’s more salty, yields a higher silver release than, for example, saliva.
So, nanosilver is likely not to be harmful for consumers, they might even be a better option than other more harmful antimicrobial chemicals and antibiotics. But I think this brings a nice opportunity for discussion about antimicrobial products. Our generation has seen such a boom in antimicrobial products that I feel we might be buying some without even realizing it. And, as much as it may help most of us feel safer by killing potentially harmful bacteria, we might also be ridding our homes of a healthy microbiota. Jessica Green has a great 5-min TED talk about what we’re doing with the air microbiota of hospitals when we try to filter everything out.
Now it’s your turn to add to the discussion:
Do you use antimicrobial products (with nanosilver or other kinds) in your home? How do you feel about them? Post your comment below!
For more information on this project:
See our newly-published paper on Environmental Science & Technology:
Quadros, Marina, Pierson Iv, Raymond, Tulve, Nicolle, Willis, Robert, Rogers, Kim, Thomas, Treye, & Marr, Linsey (2013). Release of silver from nanotechnology-based consumer products for children. Environmental Science & Technology. doi: 10.1021/es4015844
Or contact Dr. Marina Vance
The work described in this post was featured in a really insightful Nanowerk Spotlight article and is showcased on the CEINT homepage.
Other VTSuN research involving silver nanoparticles:
Kent, Ronald D., & Vikesland, Peter J. (2011). Controlled Evaluation of Silver Nanoparticle Dissolution Using Atomic Force Microscopy. Environmental Science & Technology. doi: 10.1021/es203475a
Quadros, Marina E., & Marr, Linsey C. (2011).Silver Nanoparticles and Total Aerosols Emitted by Nanotechnology-Related Consumer Spray Products. Environmental Science & Technology, 45(24), 10713-10719. doi: 10.1021/es202770m
Quadros, Marina E., & Marr, Linsey C. (2010).Environmental and human health risks of aerosolized silver nanoparticles. Journal of the Air & Waste Management Association, 60(7), 770-781. doi: DOI 10.3155/1047-32184.108.40.2060
About the Author: Marina Vance is the Associate Director for VTSuN: Virginia Tech’s Center for Sustainable Nanotechnology and a postdoctoral associate of the Institute for Critical Technology and Applied Science (ICTAS) at Virginia Tech.
Update [2 Sep 2014] Nina Quadros has recently changed her name to Marina Vance
On twitter: @marinavance
I would like to share my experience with nano stuff in commercial products. I would use this wonderful running shirt that I got from Dicks. It was just amazing and felt so good – no smell, no stain and uv proof for my uber long runs! After few meeting with nano IGEP group at VT, I wondered where the wonderness of my shirt came from. It was some nano silver anti microbial thingy!
This brought me into a fix- do I wash it until nanosilver leaches out? or do I dump it and risk exposing environment/landfills to it? or do I just go on assuming that all nano-Ag that had to leach out has already leached out after those first few washes!! (woah- ignorance was bliss!)
Interesting question Gargi.
I would add, that washing the shirt and putting in a landfill with lead to different aging effects. I could imagine a scenario that throwing out the shirt after 20 washes was actually more dangerous than disposing of a brand new shirt.
Nina, are there papers on the interactions of nanosilver and surfactants (detergents) ?
These are great comments!
Gargi, I think that, as an adult, your exposure level to the silver from the nanoparticles in your shirt is extremely low, so if anything, my research showed that it’s ok for you to keep wearing it, especially if it works for you! It’s likely that the silver will either leach out during washing or has already become silver chloride from contact with your sweat or other sources of salt, which made it pretty much insoluble. So, it’s very unlikely that you get direct silver exposure after the first use.
My biggest concern was with children, who still have many more years than us to be exposed to something that is only becoming popular now. If companies label their products correctly and specify what is the antimicrobial element in products, people can make a decision not to overload themselves on any particular kind of material.
Marjorie, I think the opposite in terms of the landfill disposal, because in my study product aging did not lead to more silver coming off. After use and repeated washing, particles may get more trapped to the product (by becoming coated with silver chloride) or might get released into the wash water.
I don’t know of specific studies on detergents, but Benn and Westerhoff published two heavily cited papers a few years ago on silver release into wash water (http://dx.doi.org/10.1021/es7032718 and http://dx.doi.org/10.2134/jeq2009.0363). The “socks” paper is quite famous amongst the nanosilver researchers.
As someone who exercises a lot and has trouble with what I call “permastink” in wicking clothing (still smells even after being washed), I find the idea of an antimicrobial shirt very attractive. I have heard that nanosilver in shirts really does help with the odor. From what I have read about permastink, it happens because the wicking fibers are so good at wicking, that the bacteria get in there and can’t get out, even when subjected to a wash cycle. My guess with nanosilver is that it must be impregnated in the fibers so that it kills the bacteria that get in there. Nanosilver on the outside of the fibers probably leaches away within a few washings, but that inside the fibers stays. In a lab test with the fibers in a culture, there may not be any effect on the bacteria in suspension. It would be the bacteria that mange to work their way into the fibers that would be zapped.
Interesting! I wonder how we could experimentally show the bacterial growth or lack thereof within fabric fibers. I bet this “inner growth” is different for different fibers, like polyester vs. cotton.