Which physical and chemical characteristics of PM are responsible for health effects? The source document for this Digest states: Answer: There is strong evidence to conclude that fine particles (< 2.5 µm, PM2.5) are more hazardous than larger ones (coarse particles) in terms of mortality and cardiovascular and respiratory endpoints in panel studies. This does not imply that the coarse fraction of PM10 is innocuous. In toxicological and controlled human exposure studies, several physical, biological and chemical characteristics of particles have been found to elicit cardiopulmonary responses. Amongst the characteristics found to be contributing to toxicity in epidemiological and controlled exposure studies are metal content, presence of PAHs, other organic components, endotoxin and both small (< 2.5 µm) and extremely small size (< 100 nm). Possibly relevant chemical characteristics include the content of transition metals, crustal material, secondary components such as sulphates and nitrates, polycyclic aromatic hydrocarbons and carbonaceous material, reflecting the various sources that contribute to PM in the atmosphere. In general, fine PM (< 2.5 µm) consists to a large extent of primary and secondary combustion products such as elemental and organic carbon, sulphates, nitrates and PAHs. Coarse PM (between 2.5 and 10 µm) usually contains more crustal material such as silicates. Toxicology Many toxicological studies, both in vivo and in vitro and in human as well as in animal systems, have attempted to determine the most important characteristics of PM for inducing adverse health effects. Some studies have demonstrated the importance of particle size (ultrafine vs. fine vs. coarse particles), surface area, geometric form, and other physical characteristics. Particle size: Studies with experimental animals have shown that both the coarse, fine and ultrafine fractions of ambient PM induce health effects (113, 129, 164). On a mass basis, small particles generally induce more inflammation than larger particles, due to a relative larger surface area (165). The coarse fraction of ambient PM may, however, be more potent to induce inflammation than smaller particles due to differences in chemical composition (129). Experimentally, inhaled ultrafine particles have been demonstrated to pass into the blood circulation and to affect the thrombosis process (45, 46). The molecular and pathophysiological mechanisms for any PM-induced cardiovascular effects are largely unknown.
Posted on: Wed, 19 Jun 2013 19:56:51 +0000
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