Air Quality Guidelines Global Update 2005 - World Health ...

126
AIR QUALITY GUIDELINES
environmental factors, including outdoor air pollution and most notably diesel
particulates, have also been a concern as these contain a variety of known human
carcinogens. Indeed, urban outdoor air pollution has been estimated to contribute
to 62 000 lung cancer deaths per year worldwide (5). Furthermore, mounting
evidence indicates that populations in less developed countries may have exposures
to indoor and outdoor pollutants that exceed those in developed countries.
Smith & Mehta (101) have estimated that an additional 16 000 deaths are attributable
to indoor particulate pollution as a result of burning coal for heating and
cooking.
In the largest study to date, the American Cancer Society included 10 749 lung
cancer deaths during the period 1979–2000 (31). A 10-μg/m 3 increase in PM2.5
was associated with an 8–14% increase in the risk of lung cancer. The risk was
higher in males than in females, higher in those with the least education, and
surprisingly higher for nonsmokers than for smokers. The increased cancer risk
remained significant after adjusting for all of these factors and for age, diet, body
mass index, alcohol intake and occupation. In addition, more recent studies, taking
into account smoking and other risk factors, have observed increases in lung
cancer associated with ambient air pollution. Furthermore, the differences in exposure
between two periods of analysis in the Harvard Six Cities Study demonstrated
reductions in mortality from cardiovascular and respiratory causes but
not from lung cancer, a disease with a longer latency period and less reversibility
(102). Despite the recent evidence indicating an impact of particulate pollution
on lung cancer, especially in developing countries, important uncertainties
remain as to confounding, errors in exposure estimates and the mechanism by
which particles could either initiate or promote the development of tumours.
Future considerations
Areas of future research are likely to include pregnancy and pregnancy outcomes
such as birth weight and prematurity; neurological diseases, given our increasing
understanding of transport of particles to the brain; and perhaps systemic diseases
such as lupus and rheumatoid arthritis that are characterized by alterations
in immune function. The relationship between increased susceptibility, genes
and environment will continue to be a highly productive area of investigation.
References
1. Brain JD et al. Variations in susceptibility to inhaled pollutants: identification,
mechanisms, and policy implications. Baltimore and London, Johns Hopkins
University Press, 1988.
2. Frampton MW, Utell MJ, Samet JM. Cardiopulmonary consequences of
particle inhalation. In: Gehr P, Heyder J, eds. Particle–lung interactions.
New York, Marcel Dekker, 2000:653–670.