The downside of nanotech: do tiny particles spell big trouble?
By Darren Quick
December 14, 2009
We talk a lot about the wonders of nanotechnology here at Gizmag. After all it’s easy to get caught up in the excitement surround the technology when it promises to revolutionize practically every area of human endeavor. Among its long list of anticipated benefits are new medical treatments; stronger, lighter materials; improved energy production, storage and transmission; and more effective pollution monitoring and prevention, just to name a few. But nanotechnology is not just something set to come about in some far off future – it is happening now. In fact, the odds are there is a product either containing, or made using nanoparticles sitting in your house right now. But the big question is, are they safe?
A nanometer is one-billionth of a meter and nanotechnology deals with particles that measure 1-100 nanometers in size. At this incredibly tiny scale, chemistry is different and nanoparticles do not behave like normal particles. Because the proportion of surface atoms increases as the size of a particle decreases nanoscale particles tend to be more chemically reactive than ordinary-sized particles of the same material. This makes it hard to predict how these tiny, tiny particles will act under different conditions, and it is this unpredictability that poses some very big questions.
Once nanoparticles enter the food chain are organisms able to excrete them or do they remain and accumulate inside the organism – and if they do, how do they behave? Do they affect natural processes and do they pose a threat? Can nanoparticles pass through biological barriers such as skin, mucous membranes or cell membranes to inadvertently enter our bodies? Currently these questions have no definitive answer. But that hasn’t stopped a great deal of money being spent developing nanotechnology, while comparatively little is being put into its potential consequences.
Silver is a good example of how unpredictably particles at the nanoscale can behave. Silver comes into contact with human skin via jewelry all the time, and is not hazardous. But silver nanoparticles are bactericidal, like antibiotics – a property that has seen silver nanoparticles used on just about anything where breeding germs aren’t desired. This includes, but is far from limited too, refrigerators, food-containers, kitchen cutting boards, baby bottles, ATM buttons, and bus handrails.
However, a series of experiments by researchers at the University of Connecticut’s Center for Environmental Sciences and Engineering has suggested that silver nanoparticles can also materially alter a person’s immunity, in some instances taking away the immune system’s ability to deal with pathogens. To date these effects have only been witnessed in a test tube, not in a human body, but researcher Christopher Perkins is stating the obvious when he says “more work needs to be done” before silver nanoparticles can be considered benign.
Titanium dioxide (TiO2) nanoparticles
There have also been concerns raised regarding the titanium dioxide (TiO2) nanoparticles now being added to cosmetics, sunscreens, and hundreds of other personal care products as well as paint and even vitamins. These particles have proven to have highly beneficial effects in blocking ultraviolet light in sunlight, but there are fears they may also be harmful to the environment by negatively affecting beneficial bacteria.
Studies have shown that Escherichia coli (E. coli) bacteria suffered a surprisingly large reduction in survival samples when exposed to even small concentrations of the nanoparticles for less than an hour. And before you go thinking that’s a good thing, you should know that although some strains of E. coli cause serious food poisoning, most strains are harmless and as part of the normal flora of the gut can benefit their hosts by producing vitamin K2 or preventing the establishment of pathogenic bacteria within the intestine.
An even more worrying study out of the University of California, Los Angeles (UCLA) has shown that TiO2 nanoparticles cause systemic genetic damage in mice. The TiO2 nanoparticles induced single- and double-strand DNA breaks and also caused chromosomal damage as well as inflammation, all of which increase the risk for cancer. The UCLA study is the first to show that the nanoparticles had such an effect. Once in the system, the TiO2 nanoparticles accumulate in different organs because the body has no way to eliminate them. And because they are so small, they can go everywhere in the body, even through cells, and may interfere with sub-cellular mechanisms.
In the past, these TiO2 nanoparticles have been considered non-toxic in that they do not incite a chemical reaction. Instead, it is surface interactions that the nanoparticles have within their environment - in this case inside a mouse - that is causing the genetic damage, said Robert Schiestl, a professor of pathology, radiation oncology and environmental health sciences, a Jonsson Cancer Center scientist and the study's senior author. They wander throughout the body causing oxidative stress, which can lead to cell death.
According to Schiestl, “the novel principle is that titanium by itself is chemically inert. However, when the particles become progressively smaller, their surface, in turn, becomes progressively bigger and in the interaction of this surface with the environment oxidative stress is induced.”
The mice were exposed to the TiO2 nanoparticles in their drinking water and began showing genetic damage on the fifth day. The human equivalent is about 1.6 years of exposure to the nanoparticles in a manufacturing environment. However, Schiestl said, it's not clear if regular, everyday exposure in humans increases exponentially as continued contact with the nanoparticles occurs over time.
It could be that a certain portion of spontaneous cancers are due to this exposure," Schiestl said. "And some people could be more sensitive to nanoparticles exposure than others. "I believe the toxicity of these nanoparticles has not been studied enough."
"These data suggest that we should be concerned about a potential risk of cancer or genetic disorders especially for people occupationally exposed to high concentrations of titanium dioxide nanoparticles, and that it might be prudent to limit their ingestion through non-essential drug additives, food colors, etc.," the study states.
However, manufacturers already use around two million tons of TiO2 nanoparticles each year. When you consider that each nanoparticle is less that 1/1000th the width of a human hair that adds up to a lot of nanoparticles. In addition to paint, cosmetics, sunscreen and vitamins, the nanoparticles can be found in toothpaste, food colorants, nutritional supplements and hundreds of other personal care products.
In yet another study on nanotoxicity, scientists found that Pseudomonas putida (P. putida) - a beneficial soil microbe - cannot tolerate silver, copper oxide and zinc oxide nanoparticles. Toxicity occurred at levels as low as micrograms per liter. That's equivalent to two or three drops of water in an Olympic-sized swimming pool, which could spell danger for aquatic life.
There is also a theoretical possibility that certain nanoparticles could pass through biological barriers such as skin, mucous membranes or cell membranes to inadvertently enter our bodies. Schiestl says TiO2 nanoparticles cannot go through skin and he recommends using a lotion sunscreen because spray-on sunscreens could potentially be inhaled and the nanoparticles could become lodged in the lungs. However, that still doesn’t address the problem of TiO2 particles being washed down the drain in homes as people bathe and ending up in municipal sewage treatment plants. From there, they can enter lakes, rivers, and other water sources where microorganisms serve essential roles in maintaining a healthy environment.
Stopping the spread
Because water discharged from sewage treatment plants is the major gateway for spread of nanoparticles to the aquatic environment scientists are focusing on how nanoparticles behave in wastewater and how that gateway might be closed off. A study by Helen Jarvie from the UK Centre for Ecology and Hydrology and colleagues showed that coating silica nanoparticles (similar to those used in ointments, toothpaste and household cleaners) with a detergent-like material made the nanoparticles clump together into the solid residue termed sewage sludge. Sludge is often stored in landfills or recycled as agricultural fertilizer. Uncoated nanoparticles, in contrast, stayed in the water and therefore remained in the effluent stream.
Cyndee Gruden, Ph.D, from the University of Toronto says that, although the public is ultimately responsible for understanding the risks of consumer products, science plays a large role in highlighting possible hazards. "It is the scientist's job to perform good research and let the findings speak for themselves," she said. And so far the promises of nanotechnology need more evaluation. "To date, it's unclear whether the benefits of nanotech outweigh the risks associated with environmental release and exposure to nanoparticles."
Thankfully, it appears the potential dangers of nanoparticles on both the environment and humans are beginning to be taken seriously. The Society of Environmental Toxicology and Chemistry’s (SETAC) North America annual meeting last month saw over 100 presentations related to nanotoxicity, while earlier this year the U.S. Environmental Protection Agency (EPA) announced it had “outlined a new research strategy to better understand how manufactured nanomaterials may harm human health and the environment.”
The EPA’s strategy outlines the goal of new, coordinated research program designed to fill the not so nano-sized gaps in the science of nanotechnology and will focus on seven manufactured nanoparticles: single-walled carbon nanotubes, multi-walled carbon nanotubes, fullerenes, cerium oxide, silver, titanium dioxide and zero-valent iron. Although the EPA admits the list of nanomaterials is obviously much larger than these seven materials, and is growing, these materials provide a starting point for the program, which will evolve as nanoscience itself evolves.
Let’s hope such initiatives are not too late, because an uncontrolled experiment to study the effects of nanoparticles on the environment and the human body is already underway around the globe. Currently, there is no answer to the question as to whether nanoparticles are safe. Regardless, the nanotechnology sector continues to develop and commercialize new nanotech products faster than scientists working in the areas of ecological and human toxicity can keep up with. Never mind. It could all be fine. Then again, in a few years the world might wake up to discover some very small particles have created a very big problem.Share
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