The word “nanotechnology” has evolved beyond a buzzword for marketers and entrepreneurs. Nanotechnology (often abbreviated “nanotech”) in some form is currently represented in yearly sales of over $32 billion in products. At present, only a few familiar consumer end products, such as sunscreens, use nanotechnology. Although promising, there are presently only a few applications of nanotechnology in the areas of medicine, food, and agriculture. This lack of applications will not remain as such much longer; the Helmut Kaiser Consultancy estimates that the yearly worldwide nanotech food market may total over $20 billion by 2010.
This trajectory for increased human exposure provides us with a narrow temporal window to develop a better understanding of nanotechnology and develop some basic safety principles. This is a lull that we must put to good use because the application of nanotechnology and development of nano-sized particles is not capital intensive (i.e., almost anyone can get started). Additionally, the application of nanotechnology to foods could be initiated by those more interested in a spike in sales than in the long-term effects on the public or the technology itself. Burdock Group is currently investing the time to develop expertise in the toxicology of nanoparticles. Often, the most difficult concept to grasp about nanotechnology is the size scale. A favorite comparison is “a nanometer is to a meter, as the diameter of a dime is to the diameter of the earth.” But at this size, some of the basic rules get changed. At the nanoscale, the physical, chemical, and biological properties of materials differ in fundamental ways from the properties of the bulk matter from which the nanosized particles (NSPs) are derived. For example, nano-particulated gold is no longer yellow, but blue in color; it is no longer chemically inert, but may act as a catalyst, and it melts at 200 °C instead of 1200 °C. Truly, it is as if another “dimension” were discovered for the properties and application of conventional substances. NSPs added to plastics or steel can make the product tens of times stronger. Electrical conductivity of substances can be greatly enhanced. Silver NSPs incorporated into clothing and food wrapping have excellent antibacterial properties. Moreover, in medicine and diagnostics, there is the promise of more directed treatment of cancer and other debilitating diseases.
However, the advantages of this promising technology cannot blind us to the potential risks; that is, if basic chemical properties are changed, it should be obvious that interactions with biological systems are changed as well. Concern that there can be a change in the fundamental safety of a NSP has given rise to a new field—nanotoxicology. The possible new effects likely to be observed with NSPs are those that are primarily involved with absorption, distribution, metabolism, and excretion. For example, NSPs can cross the plasma membranes more easily substances or pass through interstitial spaces (or, so-called “tight junctions”); in some instances, NSPs can pass through virtually impermeable blood-brain and placental barriers. Further, if NSPs are taken up by cells by non-traditional mechanisms or in increased amounts, this is an indication that normal methods of excretion may also be no longer valid. The implication is that humans may become bioaccumulators with an inability to effectively transport or excrete some NSPs.
Another to consider is the inherent toxicity of a substance and the effect of its reduction to nanoscale. For example, if the toxicity of a substance is dependent on physical contact with a cell, think about what happens at particle diameters of 10 nanometers or less, when the surface area is exponentially increased compared with an equal mass of the same substance at micro dimensions? Paracelsus’ dictum, “the dose makes the poison,” might have to be changed to, “the dose, as a function of the surface area, makes the poison.”
Lastly, if the physical properties of a substance can be changed, cannot a change also occur in the toxicity of a substance? We already know of examples where just a change in the size or configuration has changed the toxicity of a substance. For example, whereas many types of asbestos are relatively benign, we know that those that produce crystalline needles of certain dimensions, when inhaled, can produce deadly asbestosis or the cancer, mesothelioma. Food also reveals a change in toxicity related to size of constituent molecules. As an example, degraded carrageenan produces cancer in rats whereas non-degraded carrageenan does not. This finding resulted in a regulation specifying that degraded carrageenan must have an average molecular weight greater than 100,000 Daltons. Also, the number of particles in microcrystalline cellulose with a diameter of less than five microns is limited by regulation.
With all the possible new applications of NSPs, new problems are equally possible, and the new field of nanotoxicology will come of age. At the present time, the generation of NSPs is expensive, and applications are reserved for the industries where returns are highest, and in highly protected environments such as those in the medical and electronics industries. In about five years, however, the cost of producing NSPs will be substantially lower, allowing for their use in the low-margin industries, such as food and agriculture. Such as expansion of nanotechnology will introduce a greater possibility of unintentional exposure of workers in a relatively unprotected work environment, and eventually, exposure of consumers to potentially negative effects of some nanoparticles. This five-year breathing space will give us some time to develop nanotoxicology to determine where potential problems lay in order to ensure the safe application of this new technology.