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Nanoparticles have unique properties that can bring benefits to various fields, but their effects on human health and the environment are not well understood. Nanoparticles can enter the body in unexpected ways and cause biochemical reactions that damage cells and DNA. Some nanoparticles, such as carbon nanotubes, have been found to cause inflammation and injury in tissue exposed to them, similar to asbestos fibers. Studies have also shown adverse effects of fullerenes and cadmium selenide nanoparticles. Researchers are urging for more research to precede the production and marketing of products containing nanoparticles to avoid potential dangers.
Researchers have spent a lot of time and money studying new applications for nanotechnology, but relatively little has been spent on research into the effects of these particles on human health and the environment. Elements behave differently when made on an extremely small scale, so they can react to their environment in unexpected ways. They may be able to enter the body in ways they couldn’t before, affecting the brain or other tissue; since many of these elements can’t break the blood-brain barrier when in their standard form, no one really knows what will happen when they do. The shapes of the nanoparticles can also be very different from those usual for the element, causing living systems to either not know how to react to them or respond negatively.
What is Nanotechnology?
Nanotechnology is an area of science and engineering that involves the study and manipulation of particles ranging in size from 1 to 100 nanometers. A nanometer is one-billionth of a meter, with one meter being approximately 39 inches. Particles in this size range often have unusual properties and it is hoped that these can be exploited to bring huge benefits to fields such as science, engineering, medicine and computer science.
The behavior of nanoparticles
According to experts, the problem is that nanoscale elements behave differently from the larger particles in which they are normally found. For example, the properties of graphite are well known: it occupies a specific position in toxicological guidelines and is not considered a hazardous or reactive material under any normal circumstances. Nobel Prize-winning physicist Richard Smalley of Rice University has discovered carbon nanotubes and fullerenes (buckyballs) – nanoparticles of carbon – which are classified as forms of graphite because of the way the carbon atoms are arranged. These particles, however, behave in different ways from graphite, making their classification potentially dangerous.
Scientists know that substances become more reactive as their particles get smaller because the surface area is greater than the volume, providing a larger surface area over which chemical reactions can occur for a given amount of substance. An example concerns the element iron. An iron nail will not burn, but an equal amount of the element in fine powder form will spontaneously ignite when exposed to air. Similarly, substances that are normally quite inert can undergo unexpected chemical reactions in the human body or in the environment when in the form of nanoparticles.
How nanoparticles interact with living systems
Any assessment of the hazards of nanotechnology is complicated by the fact that the size and shape of nanoparticles can affect their bioactivity and toxicity. Consequently, a simple categorization based on the known properties of the elements may not be possible. Their ability to interact with living systems increases because they can often penetrate the skin, enter the bloodstream through the lungs, and cross the blood brain barrier. Once inside the body, further biochemical reactions can occur, such as the creation of free radicals that damage cells and DNA. Another problem is that while the body has built-in defenses for the natural particles it encounters, nanotechnology is introducing entirely new substances that the body would not recognize or be able to deal with.
Sometimes, the physical, as opposed to the chemical, properties of particles alone can make them dangerous in unexpected ways. Asbestos is one example. Because it is chemically quite inert, it was originally thought to be harmless and was used extensively, but when cut or broken, this material produces tiny airborne fibers that can be inhaled. It has now been established that these fibers can cause cancer when lodged in the lungs and it appears that the effect is due to their size and shape and the way they interact mechanically with lung cells.
A scientific study has found that some types of carbon nanotubes closely resemble asbestos fibers in their size and shape, and animal tests have shown that the nanotubes cause inflammation and injury in tissue exposed to them. No link to cancer has yet been proven, but in the case of asbestos, the disease may only develop several decades after exposure. Today, 3,000 deaths a year are still attributed to asbestos from decades of use. Those concerned about the possible dangers of nanotechnology are hoping to avoid a similar or even worse future scenario, especially given the growing market for nanoparticles in products as diverse as car paint, tennis rackets and makeup.
Studies on the effects of nanoparticles
In March 2004, tests conducted by environmental toxicologist Eva Oberdörster, Ph.D., of Southern Methodist University in Texas, found extensive brain damage in fish exposed to fullerenes over a period of just 48 hours at a relatively moderate dose of 0.5 parts per million — comparable to levels of other pollutants found in similar environments. The fish also showed altered genetic markers in their livers, indicating their entire physiology was affected. In a simultaneous test, the fullerenes killed water fleas, an important link in the marine food chain.
Oberdörster couldn’t say whether fullerenes would also cause brain damage in humans, but he cautioned that more studies are needed and that the accumulation of fullerenes over time could be a problem, particularly if they are allowed to enter the food chain. Previous studies in 2002 by the Center for Biological and Environmental Nanotechnology (CBEN) indicated that nanoparticles accumulated in the bodies of laboratory animals, and still others showed that fullerenes travel freely through soil and could be absorbed by earthworms. This is a potential link in the food chain to humans and represents one of the possible dangers of nanotechnology.
Other nanoparticles have also been shown to have adverse effects. Research by the University of California at San Diego in early 2002 revealed that cadmium selenide nanoparticles, also called quantum dots, can cause cadmium poisoning in humans. Cadmium is toxic in any form that can be absorbed by the body, but the tiny size of these particles can increase the risk of accidental exposure. In 2004, British scientist Vyvyan Howard published the first results indicating that gold nanoparticles could travel through a pregnant woman’s placenta to her fetus. As early as 1997, Oxford scientists discovered that nanoparticles used in sunscreen create free radicals that damage DNA.
The future
There is no doubt that nanoparticles have interesting and useful properties and can bring great benefits, but research into their possible negative effects is still ongoing and people are already being exposed to them. Workers employed in the manufacture of products containing nanoparticles are most at risk: the US National Institute for Occupational Safety and Health (NIOSH) reports that more than 2 million Americans are exposed to high levels of these particles and believe that this figure will rise to 4 million in the near future. Several groups have proposed a moratorium on the production and marketing of products containing nanoparticles and are urging research to precede rather than follow production. There are fears that strong economic pressures and market competition may take precedence over scientific prudence when it comes to public health and the potential dangers of nanotechnology.
