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We like to briefly address two special aspects: the legislative measures to limit the health impact of particulate matter exposure and the issue of indoor exposure.

It is true that the EU limit values for particulate air pollutants—currently in force in Germany too—are criticized by large parts of the scientific community. A comprehensive compilation of the currently available data has shown that a significant negative impact on the health of the population occurs already below the EU limit value of 25 µg/m3 for long-term concentrations of PM2.5 (1). Therefore, the WHO recommends using a limit value of 10 µg/m3 for PM2.5 and the US Environmental Protection Agency lowered the US limit value from 15 to 12 µg/m3 in 2013. In contrast, the consultations within the EU in 2014 did not lead to improvements in health protection and ended with no significant changes to the existing limit values. To achieve a sustained improvement of this situation, it is necessary that the medical community, among others, exerts pressure at the EU level.

However, focusing entirely on the particle mass of the PM2.5 or also PM10 particulate matter fractions will fall short of the mark, especially since the larger dust particles, which significantly contribute to this mass, have been very effectively held back by filters put into use over the last decades. PM2.5 measuring does not adequately detect so-called ultrafine particles (UFP). Ultrafine particles (particles with a diameter of less than 10 nm) are by-products of any combustion process and emitted in large quantities by cars with modern direct-injection engines in close proximity to where people live and work. Since the statutory monitoring network is not yet equipped to detect ultrafine particles, we have no data on the degree of exposure of the population to these pollutants and cannot provide any robust information about the health effects of these tiny particles either. Laboratory studies have shown that particulate matter of this size can reach the central nervous system where it may trigger inflammatory reactions (2). Therefore, the first step should be to collect more data on the UFP exposure of the population and investigate potential health effects.

Dr. Schulze addresses the issue of indoor exposure to air pollutants. This can be significant, both at home and at the workplace, and may have considerable health implications. Key determinants of exposure in the home environment are the concentrations of pollutants in the outdoor air, as those tend to penetrate comparatively unhindered into the indoor spaces even in modern homes, and specific indoor factors, such as smoking and other combustion processes (e. g. stoves and fireplaces, gas cookers), and biological material where there is mold. The study’s specific design allowed us to take into account smoking and passive smoking as confounding factors. In addition, it can be assumed that further indoor sources of pollutants are independent of outdoor air pollution concentrations. This introduces a degree of uncertainty in estimating the effects which is reflected in the confidence intervals.

DOI: 10.3238/arztebl.2015.0757

On behalf of the authors

Prof. Dr. med. Barbara Hoffmann, MPH

Leibniz-Institut für Umweltmedizinische Forschung

AG Umweltepidemiologie kardiovaskulärer Alterung und Allergien

Düsseldorf, Germany

b.hoffmann@uni-duesseldorf.de

Conflict of interest statement

Prof. Hoffmann was remunerated for the review of a related project from the Health Effects Institute. She received research funding from the Volkswagen Foundation (Volkswagenstiftung).

1.
World Health Organization. Review of evidence on health aspects of air pollution – REVIHAAP Project. Technical Report. 2013. www.euro.who.int/__data/assets/pdf_file/0004/193108/REVIHAAP-Final-
technical-report-final-version.pdf (last accessed on 12 June 2015).
2.
Block ML, Elder A, Auten RL, et al.: The outdoor air pollution and brain health workshop. Neurotoxicology 2012; 33: 972–84 MEDLINE
3.
Hoffmann B, Weinmayr G, Hennig F, et al.: Air quality, stroke and coronary events—results of the Heinz Nixdorf Recall Study from the Ruhr region. Dtsch Arztebl Int 2015; 112: 195–201 VOLLTEXT
1.World Health Organization. Review of evidence on health aspects of air pollution – REVIHAAP Project. Technical Report. 2013. www.euro.who.int/__data/assets/pdf_file/0004/193108/REVIHAAP-Final-
technical-report-final-version.pdf (last accessed on 12 June 2015).
2.Block ML, Elder A, Auten RL, et al.: The outdoor air pollution and brain health workshop. Neurotoxicology 2012; 33: 972–84 MEDLINE
3.Hoffmann B, Weinmayr G, Hennig F, et al.: Air quality, stroke and coronary events—results of the Heinz Nixdorf Recall Study from the Ruhr region. Dtsch Arztebl Int 2015; 112: 195–201 VOLLTEXT

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