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EHA : Yearkbook 2009
EHA YEARBOOK 2009 general, the susceptibility depends on the specific end point, the level of exposure, and the lengths of exposure. In particular, those with chronic cardiopulmonary disease/asthma/influenza are affected by short term/ moderate exposures, while long term/repeated exposure results in an increased risk of mortality in a broad based cohort of adults and children. Health effects due to inhalation of particles: ultrafine particles The potential hazards from the inhalation of ultrafine particles by humans are very different from those from the inhalation of larger particles, since they are inhaled into much deeper regions of the lung and they are not readily removed from the airstream of inhaled air in the upper parts of the respiratory tract. When deposited in the small containments of the alveoli region, diffusional deposition of the particles on the epithelium becomes an efficient physical mechanism. Alveolar deposition of 0.05 um particles is about 40%, compared to about 10 % for 0.7 um particles (Maynard 2000). If these particles are charged, they pose an added risk to human health, since inhaled charged particles have a five to six-fold increased probability of lung deposition than uncharged particles of the same size (Cohen & Xiong 1998). The nanoparticles deposited in this oxygen/blood exchange region can penetrate into the blood stream very quickly and efficiently. All of the studies conducted thus far demonstrate that the primary determinant of the effect of ultrafine particles is their number and their surface area, not the weight of the particles present (Morawska et al. 2003). This means that the traditional use of particulate matter weight measures is inappropriate when evaluating the likely biological effects of ultrafine particulates. It should, however, be kept in mind that it is not only the size by which ultrafine and nanoparticles differ from larger particles, but there are also substantial differences in particle chemical properties, and thus in the toxicological and carcinogenic effects they cause. As shown by recent literature reviews (Morawska et al. 2003; Morawska et al. 2007), there have been only a relatively small number of epidemiological studies conducted thus far. A total of only five international epidemiological studies on ultrafine particles have been conducted since 2003 (eight were conducted prior to this time). The current state of knowledge on the health effects of ultrafine particles can be summarised by saying that the array of epidemiological studies conducted so far does suggest that exposure to ultrafine particles is associated with respiratory and cardiovascular effects, which holds true despite considerable gaps in knowledge and some inconsistencies found between different studies. While both fine and ultrafine particles appear to affect health outcomes, such as respiratory and cardiovascular morbidity and mortality, they appear to do so independently of each other. Fine particles show more immediate effects, while ultrafine particles show more delayed effects on mortality. However, at present, the database is too limited (both in terms of number of studies and number of subjects) and geographically restricted, to allow clear conclusions on the mode of action or generalisation to other settings. Further studies are currently under way but more studies in other settings need to be initiated to improve our understanding of ultrafine particles and health outcomes. The reviews showed that there are several significant deficiencies of the epidemiological studies conducted thus far, which can be summarised as follows: n First, all studies drew on data from central monitoring stations to estimate the levels of ultrafine particles that participants in the study would have been exposed to. It is now understood that in most cases, this did not accurately represent real exposure levels and that monitoring of ultrafine particles must be done at the location where the exposure occurs. As explained above, exposure to particle number concentrations in the proximity to a road for example, can be up to 10 times higher than away from the road. n Second, the background concentrations of ultrafine particles in the various cities investigated were not sufficiently different to allow conclusions to be drawn across the studies. Some of the reasons for these deficiencies include: n a lack of scientific understanding of the nature and dynamics of ultrafine particles at the time of the studies n limited instrumental methods or capability to monitor adequately exposure to ultrafine particles n the absence of an interdisciplinary approach Ultrafine Particles: Future Directions Given that there is a poor correlation between ultrafine particles (measured by number) and fine particle mass, observed statistical independence (in the multiple regression models) is of significance. Further, given that fine and ultrafine particles often originate from common sources, have different dynamics of particle formation and accumulation and also display different observed lead-lag relationships between exposure and observed health responses, it is currently difficult to make strong inferences about independent effects, based on the epidemiological evidence provided so Air Quality and its impact on Health: (continued)
Annual Review and Yearbook 2008
EHA Yearbook 2010