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The Notre-Dame fire: how has it contributed to lead pollution in the Parisian environment?

​The Métal du Chantier Notre-Dame group, which includes researchers from the LSCE (CEA-CNRS-UVSQ), has been using the isotopic signatures of lead to reveal that the Notre-Dame fire released this metal into the atmosphere. This event caused, on the very day, a sudden peak in pollution reaching up to one hundred times the normal value.
Published on 25 November 2020

On the evening of the Notre-Dame de Paris fire, the lead in the roofing either melted or was dispersed in an aerosol form, depending on the temperature it reached. So, what was the extent of this dispersal?

Even before that fateful day, the lead contained in the roofing and spire of Notre-Dame, estimated at about 450 tons, was already a source of pollution through the leaching of rainwater, which is just one source among many others (i.e., the waterproofing joints of roofs and balconies). In Paris, this neurotoxic metal is in fact present everywhere: in runoff on pavements and facades, in atmospheric particles emitted by urban waste incinerators, and in the soil and wastewater. And even if many uses have been stopped or banned (drinking water pipes, printing type, paints or gasoline additives, etc.), lead still persists in the environment.

How can the impact of the Notre-Dame fire on the Parisian environment be determined? By using the isotopic signature of lead! This genuine geological mark is preserved all the way from the mine to the finished manufactured object, making it possible to trace the origin of the metal, even if it has been recycled.

This approach requires a good knowledge of supply routes to find all of the possible sources of lead at a given period of time. Thanks to an interdisciplinary approach applied for more than ten years in the study of the Seine basin, the researchers were able to identify the Rio Tinto mine in Andalusia (Spain) as the most probable main source of lead in the construction of Haussmannian-era Paris (1852-1870).

The isotopic signature of the lead emitted by the Notre-Dame de Paris fire was measured from samples of dust from the fire, free of any other pollution. It is close to that of lead from Rio Tinto – which is consistent with imports at the time of the last restoration of Notre-Dame in the 19th century – but also appears to contain medieval lead, such as those of Chartres Cathedral and the Sainte-Chapelle (Paris). This mixture could be explained by the recycling, in the 19th century, of the earlier roofs. Since the signatures are preserved when lead is mixed, the lead emitted by the fire was found to be derived from old lead (18%) as well as "new" lead from the Rio Tinto mine (82%). This evaluation is compatible with the archives of the Viollet-le-Duc construction site.

To study the atmospheric lead plume, the researchers analyzed samples from air quality monitoring programs (IRSN OPERA sites, complementary to those of Air Parif). These measurements show an increase – clear, but brief, and only on the day of the fire – in atmospheric lead concentrations, up to one hundred times higher than usual. The isotopic signature on that day is totally different from that of the filters before and after the fire: indeed, it superimposes exactly with that of the Notre-Dame dust.

Although the fire had a real and very short impact on the quality of air under the plume in the proximity of Paris, there is no indication at this stage that it had a lasting and overall environmental impact. Studies are continuing, particularly on sediments from the Seine River and dust from the interior of Parisian residences.

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