Ultrafine particles, a pollutant as harmful as it is invisible

As if the dangers of fine particle pollution were not enough. The National Health Security Agency (ANSES) warned, Tuesday, July 16, effects on the health of French ultrafine particles, less known to the general public than their big sister, soot carbon and organic carbon.

"New" polluters who contribute to the sad toll of tens of thousands of premature deaths in France because of poor air quality, concludes ANSES after peeling the body of science of 160 studies published since the publication in 2013 , the World Health Organization (WHO) baseline report on air pollution.

Danger for the cognitive development of the child ?

If the harmful effect of fine particles - cardiovascular problems, respiratory diseases - is widely documented and mediated, the awareness of the dangers of ultrafine particles is more recent. "These particles have been known for a long time by the scientific community, but doctors have not taken the subject for less than ten years," says Jean-Baptiste Renard, physicist specializing in fine particles CNRS, contacted by France 24.

A fine particle is, for simplicity, a dust whose diameter is less than 2.5 micrometers (more than 30 times smaller than a grain of sand) that comes from the combustion process, whether by a heater or the engine of a car. Those that are considered ultrafine have similar origins but are even smaller since they measure less than 100 nanometers in diameter (between 1,000 and 1,300 times smaller than the diameter of a hair). Soot or organic carbon is one of the two: it is classified as a fine particle, but "is found mainly among the smallest of them [ultrafine, Ed]," notes Airparif, the public body responsible for monitoring air quality in Île-de-France.

Their small size contributes to their dangerousness. "The ultrafine particles can not, for example, not be blocked by masks and, while the mucous membranes stop most of the particles, this is not the case of the finest who can thus go through the bronchi, go to the lung and then to integrate the blood network, "explains Marco Daturi, professor of chemistry at the University of Caen-Normandy, contacted by France 24. In summary," they can affect all organs of the body, including the brain, "says Jean-Baptiste Renard .

In its conclusions, ANSES points the finger at the risk that exposure to ultrafine particles can lead to the cognitive development of the child. By their ability to sneak deep into the body, these nanoparticles increase the risk that toxic substances they can carry to attach to a body organ, causing respiratory diseases and cardiovascular.

Ignored air quality measurements

These dangerous micro-powders are particularly abundant along major highways and in the metro. One of the reasons for this is that they "form during the braking of vehicles, so that the highest concentrations are found in the metro stations, where the lack of ventilation does not allow to evacuate the particles ultrafine created when stopping trains, "says Marco Daturi. Another culprit designated by Jean-Baptiste Renard is the diesel car: "The filters installed by the manufacturers block the largest particles, but not the ultrafine", notes this specialist. In this case, it is carbon soot. Worse, the filters "fragment the particles at the exit of the exhaust pipes, which makes them tend to multiply these nanoparticles", explained to the World Thomas Bourdel, radiologist doctor in Strasbourg and specialist in this pollution of the air.

These ultrafine particles know, moreover, to be very discrete: they are not taken into account by the measurements of the quality of the air. Because of their very small size, "they weigh little or nothing, and thus escape the main measuring tools that take into account the mass," says Jean-Baptiste Renard. There are sensors capable of tracking them, but "they are very expensive, and it would take a real political will to equip the measuring centers of these devices," notes the physicist.

It is for this reason that he considers ANSES's call for vigilance to be very important: it highlights the shortcomings of the current system, which ignores part of the problem of air pollution. Moreover, as the awareness of the harmfulness of these micropusts is only relatively recent, there is no normative framework. For example, although the WHO established thresholds for exposure to fine particles in the early 2000s, there is currently no equivalent for nanoparticles.