Evaluating toxicity of engineered particulate matter
Nanomaterials are materials with at least one dimension on the scale of atoms and molecules. Among these are nanoparticles (NPs) which, in fact, are that small in all three dimensions. What makes NPs so interesting has a lot to do with the ratio of surface area (SA) to volume. A sphere with a radius of one metre has a SA-to-volume ratio of three to one. For a sphere with a radius of one nanometre, the ratio is a whopping three billion to one! Having a very large SA compared to volume affects reactivity, strength and electrical properties in unusual ways. In fact, relative SA may be more important than particle composition itself. Given the explosion of research related to NPs and their applications, it is critical to evaluate potential health effects and toxicity. European researchers initiated the ‘Cellular interaction and toxicology with engineered nanoparticles’ (Cellnanotox) project to study the relationship of size and surface chemistry to effects on target organs. NPs enter the human body principally through inhalation and digestion. Primary organs studied were thus the lung and intestines. Secondary sites of interest, related to detoxification following distribution via the circulatory system, were the liver, kidneys and immune system. Scientists employed alternatives to animal experimentation including cell cultures and tissue slices. Results of toxicological tests varied dependent on the various cellular systems. A recurring theme, though, was that longer exposure resulted in greater toxicity. Exposure to NPs created oxidative stress, a pathologic condition caused by too many free radicals and reactive oxygen species. Exposure also induced an inflammatory response, a variety of reactions cells initiate in response to injury either due to agents including microbes and viruses or to physical or chemical trauma. Cellnanotox should have an impact both on future recommendations regarding policy and regulations as well as on engineers and scientists in designing materials with safety in mind.
