Researchers have spent a great deal of time and money investigating 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 may react to their environment in unexpected ways. They may be able to enter the body in ways that they could not before, affecting the brain or other tissues; since many of these elements cannot break the blood/brain barrier when in their standard form, no one really knows what will happen when they do. The shapes of nanoparticles can also be quite different from what is usual for the element, potentially causing living systems to not know how to react to them or to respond negatively.
What Is Nanotechnology?
Nanotechnology is an area of science and engineering that involves the study and manipulation of particles 1-100 nanometers in size. A nanometer is one billionth of a meter, with a meter being about 39 inches. Particles in this size range often have unusual properties, and it is hoped that these can be exploited to bring huge benefits in fields such as science, engineering, medicine, and computing.
The Behavior of Nanoparticles
According to experts, the issue is that elements at the nanoscale behave differently from the larger sized particles in which they are normally encountered. As an example, graphite's properties are well known: it holds specific position in toxicology guidelines and is not considered a hazardous or reactive material under any normal circumstances. Nobel winning physicist Richard Smalley of Rice University discovered carbon nanotubes and fullerenes (buckyballs) — nanoparticles of carbon — that are categorized as forms of graphite due to the way the carbon atoms are arranged. These particles, however, behave in ways unlike graphite, making their classification a potentially dangerous one.
Scientists know that substances become more reactive as their particles get smaller because the surface area is greater relative to the volume, providing a larger surface on which chemical reactions can occur for a given amount of the substance. One example concerns the element iron. An iron nail will not burn, but the same quantity of the element in the form of an extremely fine powder will ignite spontaneously when exposed to air. Similarly, substances that are normally fairly inert may undergo unexpected chemical reactions in the human body or in the environment when in nanoparticle form.
How Nanoparticles Interact with Living Systems
Any assessment of the dangers of nanotechnology is complicated by the fact that the size and shape of nanoparticles may affect their bioactivity and toxicity. As a result, 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 via the lungs, and cross the blood/brain barrier. Once inside the body, there may be further biochemical reactions, such as the creation of free radicals that damage cells and DNA. Another issue is that while the body has built-in defenses for 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 chemical, properties of particles may alone make them hazardous in unexpected ways. Asbestos is one example. Since it is chemically quite inert, it was initially thought to be harmless and was widely used, but when it is 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 they lodge in the lungs, and it seems that the effect is due to their size and shape, and the way they interact mechanically with lung cells.
One scientific study found that some types of carbon nanotubes closely resemble asbestos fibers in their dimensions and shape, and tests on animals showed that the nanotubes cause inflammation and lesions 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 per year are still attributed to asbestos from decades-old use. Those concerned with the possible dangers of nanotechnology hope to avoid a similar or even worse future scenario, especially considering the growing market for nanoparticles in such diverse products as car paint, tennis rackets, and make-up.
Studies on Nanoparticle Effects
In March 2004, tests conducted by environmental toxicologist Eva Oberdörster, Ph.D., of Southern Methodist University in Texas, found extensive brain damage to fish exposed to fullerenes for a period of just 48 hours at a relatively moderate dose of 0.5 parts per million — comparable with levels of other pollutants found in similar environments. The fish also exhibited changed gene markers in their livers, indicating their entire physiology was affected. In a concurrent test, the fullerenes killed water fleas, an important link in the marine food chain.
Oberdörster could not say whether fullerenes would also cause brain damage in humans, but she cautioned that more studies are necessary and that the accumulation of fullerenes over time could be a concern, particularly if they were allowed to enter the food chain. Earlier studies in 2002 by the Center for Biological and Environmental Nanotechnology (CBEN) indicated nanoparticles accumulated in the bodies of lab animals, and still other studies showed fullerenes travel freely through soil and could be absorbed by earthworms. This is a potential link up the food chain to humans and presents one of the possible dangers of nanotechnology.
Other nanoparticles have also been shown to have adverse effects. Research from University of California in San Diego in early 2002 revealed 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 may increase the risk of accidental exposure. In 2004, British scientist Vyvyan Howard published initial findings that indicated gold nanoparticles might move through a pregnant woman's placenta to her fetus. Even as far back as 1997, scientists at Oxford discovered nanoparticles used in sunscreen created free radicals that damaged DNA.
The Future
There is no doubt that nanoparticles have interesting and useful properties and may bring great benefits, but research into their possible adverse effects is still ongoing, and people are already 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 over 2 million Americans are exposed to high levels of these particles, and they believe this figure will rise to 4 million in the near future. A number of groups have proposed a moratorium on manufacturing and marketing of products containing nanoparticles and urge research to precede manufacturing rather than follow it. There are concerns that strong economic drives and competition in the marketplace may be taking precedence over scientific prudence when it comes to public health and the potential dangers of nanotechnology.