The Janus faces of nanoparticles.

There is an paradox apparent in the fact that nanoparticles have potential use in nanomedicine for imaging and therapy, whereas combustion-derived NP are thought to be responsible for adverse health effects of air pollution. The nanotechnology industry is in the process of producing a number of new nanoparticles which are as-yet unquantified with regard to both hazard and potential for human exposure. The toxicology of combustion-derived nanoparticles is developing and there is now considerable understanding of how they might drive both adverse lung and cardiovascular effects, including the importance of small size, large relative surface area and oxidative stress. Medicinal nanoparticles are being developed and tested on a case-by-case basis using testing protocols from biomaterials and drug safety and with regard to risk-benefit. There are considerable differences in physical and chemical properties and biodegradability between medicinal nanoparticles and the industrial and combustion-derived nanoparticles studied by particle toxicologists and we would anticipate that the bulk of medicinal NP types will be of low toxicity. However, to resolve the nanoparticle paradox there is a need to advance understanding of the characteristics that control acute and chronic toxicity, translocation, biodegradation and elimination of all of the types of particles likely to gain access to the human body. Much would be gained in this area by collaboration between particle toxicologists and nanopharmacologists.