Ultrafine particles

Ultrafine particles are potential mediators of the well documented adverse health effects of PM10 pollution in ambient air, and could also pose a problem in occupational scenarios. They are extremely small compared with the cellular structures of the lungs and have a large surface area per unit mass compared with the classic toxic particles. They form aggregates but readily deposit in the lungs as singlets or aggregates and in the lungs the aggregates may disaggregate. There are only a few human studies that show that ultrafine particles are harmful and the weight of evidence comes from toxicological studies. The toxicological studies of surrogate particles - such as carbon black, show very clearly greater inflammatory effects of ultrafine than large particles of the same material. The mechanism remains unclear but the large surface area of the ultrafine particles seems to lead to oxidative stress, and calcium changes in macrophages and epithelial cells that could be important in priming and activating cells for inflammation. Research into ultrafine particles has had extensive ramifications and the potential importance of the surface area as a measure of dose has been highlighted for regulatory scenarios. There are more gaps in our knowledge about ultrafine particles than there are certainties and more research is needed on the part that ultrafine particles play in the adverse health effects of PM10, the mechanisms of toxicity of ultrafine particles to the lungs, and the potential for ultrafine particle exposure in the workplace.