Impacts of environmental pollutants on childhood asthma

Peter D. Sly

Telethon Institute for Child Health Research, University of Western Australia , Perth , Australia .

Environmental pollutants, both outdoor and indoor, have been identified as a potential risk factor for both the initiation/induction and the exacerbation of asthma. Pollutants or irritants that may influence immune system development and the induction or exacerbation of asthma include: Environmental tobacco smoke; Combustion related products formed by the burning of organic fuels, including nitrogen dioxide, particulate matter and diesel exhaust particulates; Bioaerosols including molds, allergens and bacterial products (e.g. lipopolysaccharide - LPS); Air toxics including formaldehyde and other volatile organic compounds; Pesticides, PCBs and heavy metals. The relationship between air pollution exposure and asthma prevalence appears to be complex. In much of the western world asthma prevalence has increased during a period of improved air quality. There are examples of places with relatively clean outdoor environments with a high incidence of asthma, e.g. Australia and New Zealand , but low in areas of high air pollution, e.g. some Asian mega-cities. Similarly, several studies in Germany have demonstrated that asthma and other allergies are lower in the more polluted cities of East Germany compared with West German cities. There are, however, concerns regarding increases in vehicular exhaust pollutants, particularly diesel exhaust particles (DEP’s), and there is evidence of increased asthma prevalence related to the proximity to busy roads. There is also a school of thought that increased exposure to air pollution indoors may have contributed to worldwide increases in asthma prevalence. Environmental pollutants, however, can not be considered in isolation. In some developing countries an interaction has been shown between socio-economic status and exposure to pollution. In contrast to what may have been expected from studies in the Western world, an increased prevalence of asthma has been found in children attending schools in lower socio-economic areas in the presence of increased traffic density. This highlights the importance of not considering the environment in isolation and the need of measuring and allowing for regional differences in host-susceptibility conveyed by differences in genetics, nutritional status and exposure to infections. In addition, the impact of an environmental exposure will be critically dependant on the developmental state of the individual’s respiratory and immune systems.