KHK: Dust and the City

4. March 2011

Many risk factors for coronary heart disease can be lessened through lifestyle changes alone. One factor however can only be challenged by changing location: fine particulate matter.

It’s not only the World Health Organisation (WHO) which warns of the health effects of population exposure to particulate matter from diesel exhaust and other sources of combustion. In Europe, there has been a daily limit for PM10 50 µg/m3 and an allowable annual average value of 40 µg/m3 in place since 2005. (PM10 indicates the quantity of all the solid particles contained in dust whose diameter is less than 10 μm.)

But there really is no valid limit, many experts feel, because fine dust can always cause harm. Damage to the cardiovascular system, immune system and brain has long been established. Animal studies with young mice recently also showed an association with obesity, independent of diet. Exceeding the daily limit is permitted in Europe up to 35 times a year. Frontrunners (among German cities) in this respect at present are Munich and Passau, with excessive measured levels on twelve occasions in the year. The extent of this excess remains unclear.

Too thick air in many places

In many places nevertheless things are fine, one might be excused for thinking, according also to an online study in the information pages of the Federal Environmental Agency of Germany. The WHO however criticised European limits as being too high and as early as 2006 called to halve the acceptance limits for PM10 to 20 µg/m3 as the average annual limit.

For fine particulate matter with a particle size of PM2,5 , which is aspirable and therefore more health damaging, far lower limits have to apply, according to the WHO – that is, specifically, annual mean values of 10 µg/m3 and daily limit of 25 µg/m3. This directive was adopted in Europe in 2010 – however, for its implementation Germany still needs time.

Haze clogs vessels

How the vessels of many a city dweller react to particulate matter is now shown in an epidemiological investigation from a research team under Sara Adar of the School of Public Health University of Michigan. Fine particulate matter doesn’t just stop at the doorway. Researchers took digital images of the fundus of the eye of participants from the U.S. Multi-Ethnic Study of Atherosclerosis, showing the smallest arterioles and venules and related it to the measured levels of PM2,5 particles in domestic particulate pollution. The Multi-Ethnic Study of Atherosclerosis is used for research into the causes of the increased incidence of cardiovascular disease in the African American population.

The fine particulate matter measurements of over 4,600 participants aged between 46 and 87 continued for two years. Measurements of short-term air pollution took place each day before the examination.

Vessels are looking old

Both short-term and long-term particulate pollution led to narrowing of the arterioles, the statistical analysis of the data revealed. Changes of such small vessels are detectable only in the micrometer range, so that a single study may not have a predictive value. Residents of very busy streets show an average narrowing of arteries of 0.7 µm.

The researchers summarised the degree of stenosis descriptively: short-term fine-particulate pollution made vessels, in comparison to those in an unpolluted group, age by three years. Exposure to long-term pollution resulted in premature aging by up to seven years. This can also transform into danger for the heart. Three percent more heart disease in women, the researchers take as a starting point. These measured particulate concentrations in the study were generally below the level accepted by the U.S. Environmental Protection Agency (EPA); The air would therefore be considered “clean”.

To prove a causal relationship between particulate pollution and narrowed blood vessels, evidence of a plausible biological mechanism is necessary. Current investigations on the same subjects could provide something to help achieve this end, if it is the case that changes in vessel diameter come about as an outcome of particulate pollution.

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