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Air Pollution - Who Is at Risk?

In this issue of Paediatric and Perinatal Epidemiology, Basu and colleagues 1 add to a growing literature suggesting that fine particles in ambient air (particulate matter ≤2.5 microns, PM 2.5 ) increase preterm birth risk. The authors conducted an impressive array of analyses to estimate effects in California by region, maternal race and age, and indicators of social status such as maternal education and area-level poverty. PM 2.5 is commonly studied and often associated with adverse health outcomes. However, we rarely see such a comprehensive suite of PM 2.5 constituents as presented by Dr. Basu. It is an interesting approach to the question and has the potential to address a key issue – whether health effects are due to particle size/ mass (these small particles go deep into the lung and can go directly into circulation) or due to the compounds that form the particles and/or are adsorbed on the particles which themselves can be directly toxic or dissolve into circulation where they might cause systemic effects. Challenging this opportunity to shed more light on the question, here we see a differential response by region. If the particles or compounds themselves are biologically implicated in preterm birth, they ought to behave similarly in different areas of the state. However, for most compounds, the effects are greater in Northern California although the preterm birth rates are similar and the exposures are generally similar, perhaps slightly higher, in Southern California. The authors attempt to explain this regional difference based on variation in the underlying populations, but those differences do not resolve this question. There may be other factors associated with region, agricultural practices, for example, that could be explored further. Other uncertainties arise from the use of birth certificates to identify births within 10 km of a monitor and monitor data that is typically sparse. Compounds detectable at 30% 75% used. PM 2.5 tends to be a regional pollutant with broad some the concern related to the non-specific geographical linkage, concentrations will due to (traffic,