The National Health Security Agency (Anses) was commissioned in 2019 by the public authorities to carry out a study on the feasibility of developing "guide values for indoor air (VGAI)" in "underground railway enclosures".
Seven cities in France have underground metros: Lille, Lyon, Marseille, Paris, Rennes, Rouen and Toulouse.
The rate of particles in the air is "on average three times higher than in urban outdoor air" notes ANSES, mainly due to friction with the tracks, especially when braking.
The dust is also regularly resuspended as the trains pass.
But after reviewing the available data, ANSES considers that it cannot define such "VGAI", based solely on health criteria, for lack of a sufficient number of studies.
It therefore proposes instead air quality "indicators", determined in particular according to the respective durations of journeys on the various networks and which "integrate exposures over a day in different environments - at home, at work and in the transports".
The accumulation of these particle concentrations should comply with the exposure standards set by a 2008 European directive on air quality and if possible those of the WHO, stricter than EU regulations and tightened in 2021 to take into account account the most recent knowledge on health impacts.
In addition, the agency recommends strengthening air quality measurements in these underground networks, which are far from being generalized.
The available measurements suggest that European regulations are "generally respected," explains Marion Keirsbulck of ANSES, who stresses that "this is much less the case" for WHO values.
To improve the situation, it is necessary to continue the measures taken by the operators and "to tackle the emission of these particles, by replacing rolling stock, changing braking systems and improving ventilation", reports his side Eric Vial, director of risk assessment at ANSES.
According to the authorities, air pollution is responsible for some 40,000 premature deaths per year in France.
© 2022 AFP