I hope that the investigation on Nanotechnology will consider seriously those features that concern non-specialists and not just dismiss these concerns as ill informed or Luddite.

First, it is known that chemical reaction rates often increase with increase in surface area so that particulate size can have a dramatic effect on surface reaction rates and as a consequence chemical reactions that were previously considered unlikely suddenly can become likely. Finely divided powders for example are known to explode when the normal substance is considered innert. The ratio of surface area/particulate mass increases with decreasing size. Changing from the microscale to the nanoscale might then increase reactivity rates by a factor of 1000. Could one achieve mini-explosions of certain mixtures which had previously been thought completely safe? If these mini-explosions occurred how damaging might they be? What about other reaction rates that are normally not even considered because of their improbability under normal conditions?

Second, it is believed that small particles can behave as carcinogens when larger particles of the same substance are benign. I understand that the fumes of combusted diesel are considered ‘unsafe’ because of the small particulate size of the components of combustion. There has been concern over depleted uranium vapours when there would be much less concern over depleted uranium chunks. The minute particulate size is of course a potential hazard when filtering. Micron filters are well known for clean rooms but I do not know how nanoscale filters are progressing. I understand that there are high pressure 'nanoscale' filters for purifying water but what about filtering out nanoscale aerosols?

Third, I do not believe that we know how nanoparticles diffuse through the skin and through the body. I would not knowingly advise positively on the use of nano-particles in cosmetics unless I was sure that long term studies were secure and showed no hint of long term difficulties. How often do we hear, many years later, of difficulties when the experts have all declared a product to be safe? As someone whose wife luckily escaped from being prescribed thalidomide when pregnant, I remember such difficulties vividly. It would be surprising if nanotechnology did not offer similar upsets unless appropriate care and humility is observed.

There are nanotechnology engineering projects where the nanoscale objects are firmly anchored to microscale or larger objects perhaps giving such benefits as increased computer storage capacity or similar commercial benefits. The non-specialist can easily be convinced that this is safe process similar to binding chemicals. For exmple, Gallium arsenide is much safer than having the gallium and arsenic separately. However it would be nice to know that even this aspect of nanotechnology will be carefully considered and that concerns by less well informed not just dismissed. It will however surely be the free ranging nanoscale objects that will cause most concern and controversy over their safety. It may not be easy to steer between a Luddite reaction and a capitulation to the brave new technological world, especially when money, jobs and business are at risk. However a major disaster in an industry can cause catastrophic long term damage - De Havilland never recovered from the Comet metal fatigue disasters. I submit that we probably know less about the nano-scale than we did about metal fatigue at that time.

John Carroll
Department of Engineering
University of Cambridge