Ultrafine particles

here is a long history of disease caused by inhaled particles that stretches from Agricola and Paracelsus in the 14th century up to the present. 1 In this century the twin scourges of asbestos and crystalline silica (quartz) have exerted a terrible toll of death and disease.The bad old days when these dust related lung diseases were unbridled are gone but as we enter the 21st century a new particle type-the ultrafine particle-has emerged as one with a potential role in causing disease.Ultrafine particles have been the subject of several recent reviews. 2 3 0 c ULTRAFINE PARTICLES Particles that are less than 100 nm in diameter are commonly defined as ultrafine.However, all particle populations that are found in the air are polydispersed-that is, they comprise particles with ranges of diameters that are usually summarised as mean or median diameter.There is no reason at the moment to think that there is much diVerence between a 90 nm and a 110 nm particle in ability to have an adverse eVect and there is little evidence for the cut oV point for the ultrafine eVect.Ultrafine particles are very small compared with the cellular structures and so this may be important in the apparent problems they present to the lung (fig 1).Particles of diesel exhaust may be taken as an example of an ultrafine particle, albeit complex.They are largely insoluble because of the particulate carbon core, commonly the size of singlet diesel particles, 10-20 nm.However, they tend to group into aggregates with sulphates, metals, and hydrocarbons. 4 Particles of diesel soot are ubiquitous in urban air and contribute to particulate air pollution of aerodynamic diameter 10 µm (PM 10 ).However, ultrafine particles in urban air could come from a range of sources other than diesel soot.For experimental purposes toxicologists have used several standard ultrafine particles such as titanium dioxide and carbon black for their studies.