The lead of Notre-Dame
The fire of Notre-Dame de Paris on April 15, 2019 not only almost destroyed forever one of the most beautiful jewels of medieval Gothic art, but its consequences raise an important environmental problem: lead poisoning.
The spire inaugurated in 1859 by Eugène Viollet-le-Duc was built of oak wood and contained 250 tonnes of lead. As for the framework made of century-old oak wood, it was covered with 1326 sheets or lead tiles for a total weight of 210 tons.
Why lead?
Lead is a metal that has been known for a very long time since it was already used as pigments in prehistoric tombs. Grey in colour, it quickly becomes covered with a layer of greyish-white oxide. Its low melting point, corrosion resistance and malleability made it suitable for making everyday objects such as plates, glasses and other decanters. It was also used to make water supply pipes, as hydraulic distribution by means of Roman aqueducts was very developed at the time.
Lead exists in different forms:
– Metal: fusion 327°C, boiling 1740°C, volatilized from 500°C. They are found in old pipes, channels and balconies of historic monuments, battery accumulator plates, tin-lead solder alloy. It should be recalled that the lead shield has still not found a substitute to protect against gamma rays;
– Inorganic lead: pigments for paints, varnishes, enamels, ceramics,
Oxides and hydroxide (Pb tetraoxide (“minium”) sometimes still used
Pb salts (chromates, silicochromates, sulfochromates….
Hydrocarbonate (ceruse = colouring agent for oil paints)
– Organic derivatives: Pb tetraethyl, Pb tetramethyl (anti-knockers in gasoline to increase octane number). Now we only use unleaded petrol.
Currently, the sectors of activity exposed to lead are those of industry (manufacture and recycling of batteries, recycling of electronic products, plasturgy, manufacture of special glass…), crafts (manufacture and repair of stained glass, pottery, art foundry, jewellery…), shooting ranges (hunting pellets are made of lead alloyed with arsenic and antimony).
Lead toxicity
The toxicity of lead is partly responsible for the fall of the Roman Empire due to the poisoning and decay of the Roman elites by lead from water pipes. On the other hand, these same lead pipes were highly desired by the barbarians who stole them, depriving the Roman populations of water at the same time.
Lead is toxic to the body, even in low doses: it binds to the nervous system, bone marrow and kidneys. It gives a disease called “Saturnim” in reference to the planet Saturn, the symbol of lead in alchemy. Exposure to lead is particularly severe in children and pregnant women whose foetuses are severely affected.
Lead enters the digestive and respiratory tract, skin, mucous membranes, and placenta. Ninety per cent is stored in bone with a half-life of 20 to 30 years and is sometimes released long after exposure, which explains why the effects of intoxication may be delayed. Lead poisoning is measured by “lead levels” which should not exceed 50 micrograms per litre of blood in children and adolescents under 18 years of age. But this threshold is discussed because beyond the quantity it is also the duration of exposure that matters. The presence of lead in the blood shows recent contamination, while old contamination is measured by the presence of lead in the bones.
The symptoms
Acute intoxication is rare because it corresponds to a blood lead level above 1000 µg per litre.
Chronic intoxication is responsible for significant neurological effects such as encephalopathies, mental disorders, behavioural disorders, hearing and visual disorders and peripheral neuropathies. It also manifests itself in abdominal pain syndrome, kidney disease, cardiovascular, hepatic and metabolic effects. Hematologic toxicity results in anaemia. It also affects reproduction by reducing fertility in men. In the foetus, it causes abortions, premature deliveries and in children, psychomotor and mental development delays.
Lead is reported to be carcinogenic (Group 2A for IARC).
The treatment
It always begins with stopping the exposure (renovation of old homes) where children ingest chipped paint or drink water from lead pipes).
Dispose of clay, tin, soldered silver or decorative dishes, pottery and crockery. Avoid kohl type cosmetics. A chelating treatment (EDTA for example) can be implemented, accompanied by an infusion of hyperhydration.
Back to Notre Dame
The fire was of rare violence and the yellow smoke plumes may have reflected the formation of lead oxide particles. As they fell, these particles contaminated areas well located around the cathedral: very high lead levels in the grounds of the square and the surrounding public gardens as well as in the grounds of the schoolyard of the Saint-Benoît Street school complex. Residents in areas where lead concentrations have been measured high were asked to clean their homes with wet wipes to remove deposited lead particles to avoid repeated contact with lead that could lead to lead poisoning. A one-time exposure under these conditions cannot lead to lead poisoning.
Out of 175 children living around Notre Dame, only 2 had a blood lead level above 50 µg/L, one of them living in a family environment with many sources of lead. These children will be followed up but no treatment has been prescribed.
The City of Paris has undertaken clean-up work either by applying a gel that absorbs lead to contaminated soil, which must be removed three days later after drying, or by cleaning with high-pressure jets containing surfactants.
Workers working on the building consolidation site had their blood lead levels checked and none of them was contaminated. It is now important to protect them themselves but also to ensure that no particles can escape from the site: this is why drastic measures have been put in place, such as the presence of foot baths, decontamination showers, the wearing of disposable clothing, and the implementation of strict entry and exit protocols.
Two other concerns remain, however:
– What happened to the particles projected into the atmosphere far from Notre-Dame?
– If the vaults were to collapse, the effect would be comparable to that of the twin towers in New York with the formation of a huge amalgam of dust and the release of a number of lead particles that could be multiplied by 1000 compared to what was emitted during the fire!
Photo by Mathieu Perrier on Unsplash
Autor: Prof. François Renaud