Fine dust and nitrogen oxides make you sick? This claim is not proven, writes a group of over a hundred pulmonologists in a position paper - and thus fueled once again the passionate debate on driving bans in Germany.
According to the medical profession, the arguments that advocate limits and driving bans are based on a misinterpretation of scientific data.
- The World Health Organization (WHO) and the EU had recently presented figures showing that some 440,000 people in Europe died prematurely from air pollution.
- The Federal Environment Agency also warns about 50,000 lost years of life in Germany due to nitrogen oxides.
- Researchers from the Helmholtz Center as well as the German Society of Pneumology (DGP) also believe that nitrogen dioxides are harmful to health.
In this country, nitrogen oxides (NO2) are subject to a limit of 40 micrograms per cubic meter of annual average air - it is exceeded in various cities. According to the Federal Environment Agency, since 2012 no exceedances of the limits for particulate matter have occurred.
"It is very likely that the scientific data leading to these seemingly high numbers of deaths contain a systematic error," writes lung specialist Dieter Köhler, formerly chairman of the DGP, in his statement, which has been signed by 113 other specialists.
An important mistake is therefore: The joint occurrence of diseases and high particulate matter and nitrogen oxide levels are not only described, but placed in a causal relationship. This is indeed not allowed in so-called epidemiological studies, because they serve the purpose of observing. As a result, scientists can then hypothesize the causes and have to check them with other methods.
This is exactly what is difficult with nitrogen oxides: the substances are corrosive irritant gases. However, their impact on health is difficult to isolate. This leaves only the observation that people in regions with high nitric oxide concentrations are more likely to go to hospital with asthma, cardiovascular disease or chronic bronchitis. But this is not yet proven that the nitrogen oxides are actually the cause.
Fine dust gets deeply into the respiratory tract
The situation with particulate matter is different: Here it is proven that the small particles , which depending on their size can reach the middle of the respiratory tract, can damage their health . The doctors also doubt that in their statement with different arguments.
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Köhler and Co. argue: "Pulmonary physicians see deaths from COPD and lung cancer every day in their practices and clinics, but deaths from particulate matter and NOx, even with a careful history, never." According to the high mortality, which results from the WHO figures, the phenomenon would have to be noticed at least as an additional factor in lung diseases.
Fine dust - what is it?
- Particulates are particles smaller than ten micrometers (PM10), with one micrometer equivalent to one millionth of a meter. These particulate matter remain largely in the upper respiratory tract, so the throat, the trachea or the bronchi. Annual average values of 20 micrograms of particulate matter per cubic meter of air (μg / m³) should not be exceeded.
- Since 2008, a distinction is made between dust grains with a diameter of less than 2.5 micrometers (PM2.5). PM2,5 reach the alveoli. For this purpose, a limit of 10 μg / m³ applies.
- There is also the notion of ultrafine dust (UFP, ultrafine particles) discussed in connection with gasoline engines. This refers to even finer grains that are smaller than 0.1 microns. The ultrafine particles can pass into the bloodstream and thus, in principle, reach all body regions and cause damage, for example, through inflammatory processes and arteriosclerosis.
- In principle, fine dust is formed everywhere, where dirt is whirled up. The vast majority comes from natural sources. For example, volcanoes blow large amounts of particles into the air. Forest fires and desert sand also contribute to the dust and particulate matter in the air. Over time, the particles are distributed widely in the atmosphere, so that the load with the distance to the source decreases significantly depending on the weather.
The doctors also criticize that various confounding factors such as smoking, alcohol consumption, physical activity, medical care or medication were not meaningfully taken into account in the studies - although these significantly influenced the health.
An example can explain this: It is quite conceivable that people who live on busy roads can not afford a better residential location. It is also known that people on low incomes smoke more often and drink alcohol, eat less and move less. So what causes lung diseases in them? Is it really fine dust and nitrogen oxides from the traffic? Or maybe the other factors? Or everything together? It is not easy to make a simple statement about cause and effect.
Meaningful criticism
Other scientists have already criticized that numbers on premature deaths, as the EU uses them, are misleading. Because what does actually mean prematurely? One year, one day or one minute? Instead, one should speak better of lost life. This is less striking, but come closer to reality.
According to own data Köhler belongs to no interest group. He and his colleagues want to serve with the statement "the objectification of the discussion". The goal of the authors was to promote measures to avoid pollutants. "However, they currently do not see any scientific justification for the current limits for particulate matter and NOx."
Conclusion: Even if arguments of the doctors can be disproved, for the scientific discourse the contribution makes sense. It is inherent in science to doubt theses, results, and above all interpretations, to offer other explanations. This does not mean that the antithesis is true. But through the discourse, one approaches reality - science can not offer more anyway.