# Did the 2019 Notre-Dame Cathedral Fire impact the lead contamination of sediment in the Seine River in Paris, France?

Olivier Evrard, Rémi Bizeul, Yangjunjie Xu-Yang, Sylvain Huon, Laurence Le Callonnec, Anthony Foucher, Sophie Ayrault

► To cite this version:

Olivier Evrard, Rémi Bizeul, Yangjunjie Xu-Yang, Sylvain Huon, Laurence Le Callonnec, et al.  
Did the 2019 Notre-Dame Cathedral Fire impact the lead contamination of sediment in the  
Seine River in Paris, France?. Journal of Hazardous Materials Advances, 2026, 21, pp.101072.  
10.1016/j.hazadv.2026.101072. cea-05507162

HAL Id: cea-05507162

https://cea.hal.science/cea-05507162v1

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# Did the 2019 notre-dame cathedral fire impact the lead contamination of sediment in the Seine River in Paris, France?

Olivier Evrard<sup>a,∗</sup>, Rémi Bizeul<sup>a,†</sup>, Yangjunjie Xu-Yang<sup>a,‡</sup>, Sylvain Huon<sup>b</sup>, Laurence Le Callonnec<sup>c</sup>, Anthony Foucher<sup>a</sup>, Sophie Ayrault<sup>a,‡</sup>

## ARTICLE INFO

### Keywords:

- Fallout radionuclides

- Trace elements

- Lead isotopes

- Fingerprinting

- Source-to-sink

## ABSTRACT

The fire that affected Notre-Dame Cathedral in Paris in 2019 has reignited concerns about metal contamination including lead (Pb) in the city. The current research investigated the potential contribution of this event to the contamination of sediment transiting the Seine River. To this end, sediment deposits were collected in Paris just after floods in 2016 (i.e. before the fire), as well as in 2020 and 2021 (i.e. after the fire). They were analysed for fallout radionuclides, organic matter, metal concentrations and Pb isotopic ratios. Results showed that the material deposited by the flood exhibited contrasted characteristics and contamination levels depending on the flood. The major flood event that took place in June 2016 mainly consisted of surface recent material from the upper reaches of the river. This likely explains the large homogeneity of sediment across Paris and the relatively low metal contamination. Then, the occurrence of a lower magnitude flood event in 2020 led to the deposition of a large majority of older subsurface material, likely resuspended from the channel or eroded from the banks. This material showed higher contamination levels than in 2016. Pb levels were particularly significantly higher around Notre-Dame Cathedral. Some samples displayed Pb isotopic signatures that may coincide with those of dust from the Notre-Dame Fire ($^{206}$Pb/$^{207}$Pb: 1.1669–1.1685). Finally, in 2021, another winter flood depositing a majority of subsurface material occurred. Overall, the metal contamination levels measured in the material deposited in 2021 were lower than in 2020, except for the sample collected near the Eiffel Tower. These results demonstrate the negligible impact of the Notre-Dame fire on the Pb contamination. In the future, sediment should continue to be monitored to avoid any potential mistrust from the general public, as three bathing sites have been reopened to the public in summer 2025.

## Introduction

The fire that affected the Notre-Dame Cathedral in Paris on April 15, 2019 led to the burning of large quantities of lead, which was a significant component of the roof and the spire of the historic building. It is estimated that 460 tonnes of lead (Pb) covered the building, and that between 138 and 1000 kg of Pb may have been emitted into the atmosphere during the fire (Tognet and Truchot, 2019; Van Geen et al., 2020). Elevated Pb levels (0.002–0.077 µg g⁻¹ after the fire compared to 0.009 µg g⁻¹ before 2019) were also measured in honey samples collected in beehives across Paris City (Smith et al., 2020). These levels remained below the maximum Pb content (< 0.10 µg g⁻¹) permitted by

the European Union legislation. Although it was demonstrated that the lead found in honey did not originate from the fire (Briard et al., 2023) and that no health impact was to be expected (Vallée et al., 2021), this situation has raised concerns among the local Parisian population regarding the environmental and health impacts of this sudden and potentially substantial release of contamination, as the air, the streets and the local products may have been contaminated by these emissions and their fallout (Bouguerra, 2019).

High concentrations in Pb (210–799 mg kg⁻¹) had already been documented in soils (Gasperi et al., 2018), in nearby buildings in Paris, as well as in sediment core samples (36–460 mg kg⁻¹) collected in the Seine River before the 2019 fire (Ayrault et al., 2012). Analysis of

<footnote><sup>a</sup> Laboratoire des Sciences du Climat et de l'Environnement (LSCE/IPSL), Unité Mixte de Recherche 8212 (CEA/CNRS/UVSQ), Université Paris-Saclay, Gif-sur-Yvette, France</footnote>

<footnote><sup>b</sup> Sorbonne Université, Institut d'Ecologie et des Sciences de l'Environnement de Paris (IEES), Paris, France</footnote>

<footnote><sup>c</sup> Sorbonne Université, CY Cergy Paris Université, CNRS-INSU, Institut des Sciences de la Terre Paris, ISTE>P, F-75252 Paris, France</footnote>

<footnote>* Corresponding author.</footnote>

<footnote>E-mail address: olivier.evrard@lsce.ipsl.fr (O. Evrard).</footnote>
sediment archives collected in the floodplains along the lower reaches of the river revealed that peak contamination levels of Pb and other metals were reached in the 1960s (Ayrault et al., 2014b; Meybeck et al., 2007; Vrel et al., 2013). Over the following decades, these concentrations decreased, primarily due to the deindustrialization observed in the Paris Metropolitan area (Lestel et al., 2023). The occurrence of a widespread flood in June 2016 and the analysis of the metal contamination in flood sediment deposits during this event confirmed this downward trend (Le Gall et al., 2018), despite the remobilisation of older contaminated material in several Seine tributaries upstream of Paris. The analysis of material deposited by the 2016 flood with fallout radionuclides (including ⁷Be, ²¹⁰Pbₓs and ¹³⁷Cs) demonstrated the different age and origin of this older contaminated sediment, contributing to a better contextualisation of the nature and the quality of the material mobilised by the flood in the Seine River's different tributaries. The 2016 flood was the largest event that occurred since the removal of the mills and dams from these upper tributaries in order to comply with the European Union Water Framework Directive's requirement for the restoration of the ecological continuity. Consequently, this flood remobilised old – contaminated material that had likely been stored in these river reaches for several decades, which explains why the sediment deposited in these locations was found to be the most contaminated in the basin. Nevertheless, due to the dilution of this sediment with less polluted material originating from other tributaries including the Marne River, the metal levels including Pb found in sediment deposited by the 2016 flood in Paris remained at relatively low levels (48–69 mg kg⁻¹) (Le Gall et al., 2018).

However, the occurrence of the Notre-Dame Cathedral fire in April 2019 may have interrupted the downward trend in metal/Pb contamination trend observed in sediment archives collected along the Seine River since the peak recorded in the 1960s (Ayrault et al., 2012). Indeed, atmospheric modelling studies showed that the wind plume may have disseminated Pb contamination up to 50 km from Paris (Tognet and Truchot, 2019). The fire Pb isotopic signature was identified 15 km from Paris (Le Roux et al., 2019). Furthermore, van Geen et al. (2020) estimated that most of the fallout occurred within 1 km from the fire and that the main source of exposure would be the dust deposited during and immediately after the fire. Nevertheless, the potential impact of the fire on Pb concentrations in sediment transiting the Seine River has yet to be investigated, as the river has always been the main outlet for exporting contaminants produced in the city (Meybeck et al., 2007).

Following the fire, two significant winter flood events occurred in 2020 and in 2021, leading to substantial bank overflow along the Seine. Accordingly, the objective of the current research is to analyse the fine sediment material deposited by these floods along a transect in downstream direction in order to determine whether the 2019 fire impacted the metal contamination of sediment transiting the Seine. Due to the widespread use of Pb in Paris, analysing Pb concentrations alone is insufficient and should be complemented by data on the Pb isotopic composition to detect a potential change in Pb sources after the fire (Briard et al., 2023). The contextualisation of sediment deposits in terms of organic matter composition and source/age derived from fallout radionuclide measurements will also be conducted based on the multi-proxy analysis of samples.

## Materials and methods

### Study area

The Seine River drains a basin with a surface area of 75,000 km², accounting for 18 % of metropolitan France. In this area, sedimentary carbonate rocks make up most of the basin's lithology (~93 % according to Meybeck et al. (1998)). However, the uppermost part of the basin, in the Morvan area, is also composed of crystalline igneous rocks. The Seine's main tributary is the Marne River (drainage area: 13,160 km²). The two rivers converge a few kilometres upstream of Paris. Cropland

and grassland are the main land uses in the upper areas (Fig. 1.A). The Seine Basin has a population of 18.3 million, which is unevenly distributed, with population densities ranging from 15 inh. km⁻² in the most rural areas to 27,000 inh. km⁻² in Paris City (Tockner et al., 2021).

The current research focused on a 7826-m long section of the Seine River across Paris, starting from the Pont de Tolbiac bridge (Lat.: 48°49'57.468"; Long.: 2°22'46.952") and ending at the Eiffel Tower (Lat.: 48°51'35.388"; Long.: 2°17'36.106")). Along this transect, flood deposits were collected to reflect the characteristics of sediment transported in the Seine River across Paris.

### Flood characteristics

The current research investigated three main floods, including the exceptional event of June 2016 (Le Gall et al., 2018), which occurred before the Notre-Dame Cathedral fire in April 2019, and the subsequent winter floods that occurred in March 2020 and in February 2021. River flow rates are being continuously measured at the Paris-Austerlitz hydrographic station (Fig. 1.B), and Table 1 compares the maximum flow rates recorded for the three floods along with the average flow rate values calculated for the 1985–2011 period.

### Sample collection

Recent and fine sediment deposited during the recession stage of the last flood were collected rapidly after the floods at six to thirteen locations on the channel bank roads (with deposits showing a thickness between 1 and 5 cm) along the Seine River in Paris. The samples were collected using a plastic spatula to avoid metal contamination. Five to ten subsamples were collected at each location and placed in a plastic bag. These were then thoroughly mixed to provide a homogeneous sample of the material deposited at each location. Due to logistical and security reasons, it was not possible to conduct sampling systematically at the exact same locations after the three flood events. However, care was taken to cover the entire transect along the Seine River, including sites located both upstream and downstream of the Île-de-la-Cité where the Notre-Dame Cathedral is situated (Fig. 1.B).

Samples were oven-dried at 40 °C for ~2 days, then dry-sieved to 2 mm and wet-sieved to 63 µm in order to minimize any potential issues associated with changes in particle size (Laceby et al., 2017).

### Sediment organic matter composition

Previous studies showed that the Seine River sediment mainly consist of quartz (~30 %), calcite (~50 %) and clay minerals such as kaolinite and montmorillonite (up to ~20 %) (Chen et al., 2014; Roy et al., 1999). All Ca-carbonates (including limestone and shells fragments) were removed from the <63 µm size fractions to characterize their total organic matter and clay-bound organic matter content, through total organic carbon (TOC) and total nitrogen (TN) concentration and δ¹³C - δ¹⁵N stable isotope measurements. Sediments were carefully treated by the drop-to-drop addition of a 1 N HCl solution under constant agitation to prevent leaching effects on sedimentary organic matter. The dissolution process was carried out at room temperature with repeated pH control measurements so that the value never fell below 3.0 (Huon et al., 2002). After pH stabilization at 3.0 during 2 to 3 days, a value corresponding to the full dissolution of carbonates, all samples were rinsed six times in deionized water to remove dissolved salts. The solid residues were recovered by high velocity centrifugation (2500 rounds.mn⁻¹) for 15 min. each and dried at 40 °C. The EA-IRMS analyses were conducted on finely ground aliquots of these decarbonized samples. All measurements were performed with a continuous flow Elementar VarioPyro Cube Elemental Analyzer (EA) coupled to a Micromass Isoprime Isotope Ratios Mass Spectrometer (IRMS) facility at the Institut d'Ecologie et des Sciences de l'Environnement in Paris, France. Oxygen for combustion was injected during 70 s (30 ml.min⁻¹) and temperatures were set at 850 °C.
<figure><img src="image_3.png" /><figcaption>**Fig. 1.** (A) Location of the Seine River Basin in France and main land uses, (B) sampling locations of flood deposits along the Seine River in Paris City after the floods that took place in 2016, 2020 and 2021.</figcaption></figure>

<table><caption>**Table 1**
Maximum flow rate for the three studied floods and average monthly flow rate calculated for long term records (Source: http://www.hydro.eaufrance.fr/).</caption><thead><tr><td>Event/period under consideration</td><td>Flow rate (m<sup>3</sup>.s<sup>-1</sup>)</td></tr></thead><tbody><tr><td>June 2016 (peak)</td><td>1750</td></tr><tr><td>March 2020 (peak)</td><td>570</td></tr><tr><td>February 2021 (peak)</td><td>1300</td></tr><tr><td>Monthly mean in February (1985-2021)</td><td>811</td></tr><tr><td>Monthly mean in June (1985-2021)</td><td>336</td></tr></tbody></table>

and 1120 °C, for the reduction and combustion furnaces, respectively (Agnihotri et al., 2014). Analytical precision and repeatability were controlled with tyrosine samples calibrated against international standards (Coplen et al., 1983). In the current research, the mean uncertainties were 0.2 mgN.g⁻¹ for TN, 0.18 mgC.g⁻¹ for TOC, 0.1 ‰ for δ¹³C and 0.3 ‰ for δ¹⁵N.

## Geochemical analyses

Approximately 100 mg of sediment was successively digested by adding HF (4 mL, 47–51 %) and HClO₄ (2 mL, 65–71 %) at a first step, HCl (3.75 mL, 34–37 %) and HNO₃ (67 %, 1.25 mL) at a second step, in a closed Teflon vessel on hot plates (Digiprep, SCP Science). Samples were evaporated near to dryness between each step. Ultrapure reagents were used, and a reference material (IAEA lake sediment SL1) and a chemical blank were digested in the same way as the sediment samples in order to control mineralization efficiency and evaluate the potential contamination during digestion and analysis. The major, minor and trace elements concentrations (in mg.kg⁻¹) were determined using inductively coupled plasma mass spectrometry instrument (i.e., ICP-MS, X Series, CCT II+ Thermoelectron, France (2016 flood samples), Le Gall et al. (2018); iCAP™ TQ ICP-MS, Thermo Scientific™, France (2020 and 2021 flood samples; Briard et al., 2023). The stable radiogenic lead isotope (²⁰⁶Pb, ²⁰⁷Pb, ²⁰⁸Pb) ratios were determined in the solutions prepared for the elemental concentration analysis using the same

instrument, following the protocol detailed by Le Gall et al. (2018) and Briard et al. (2023).

## Calculation of enrichment factors

In order to compare metal concentrations measured in sediment samples collected during different campaigns and at contrasting sites, metal enrichment factors were calculated to quantify metal enrichment relative to the local geochemical background. Metal concentrations were normalized to Al to minimize potential residual differences in particle size between samples (Le Cloarec et al., 2011), and enrichment factors were calculated according to Eq. (1):

$$EF = \frac{\left(\frac{M}{Al}\right)_{sample}}{\left(\frac{M}{Al}\right)_{background}} \qquad (1)$$

Where EF is the enrichment factor for the metal of interest, M is the metal concentration measured in the sediment sample, (M/Al)sample the elementary ratio for the sample and (M/Al)background the elementary ratio for geochemical background. Geochemical background data for the Seine River basin were taken from Le Cloarec et al. (2011).

## Geochemical compositional data

For compositional data, the centered log-ratio(clr) transformation was calculated before applying multivariate techniques based on the following equation where D is the number of elements and gm(x) is the geometric mean of the D parts:clr(x) = [ln x₁ gm(x),...,ln xₚ gm(x)]

Principal components analysis was then computed on the TQ-ICP-MS clr transformed data, using the “acomp” (closure operation) and “princomp” (principal components analysis projection) functions provided by the “compositions” package, which has been specifically designed to analyze compositional data in R software (Van den Boogaart
and Tolosana-Delgado, 2013).

## Fallout radionuclides

Fallout radionuclide ($^{137}$Cs, $^{7}$Be, $^{210}$Pb) activities were also analysed at the Laboratoire des Sciences du Climat et de l'Environnement, Gif-sur-Yvette, France. The activities of $^{210}$Pb (46.5 keV), $^{7}$Be (477.6 keV) and $^{137}$Cs (661.7 keV) were determined by gamma spectrometry using the low background Germanium Hyper Pure detectors available at the laboratory. The $^{210}$Pb$_{xs}$ activities were calculated by subtracting the supported $^{210}$Pb activity (determined using two $^{226}$Ra daughters, $^{214}$Pb (average count number at 295.2 and 351.9 keV) and $^{214}$Bi (609.3 keV)) from the total $^{210}$Pb activity. For each sample, 15 to 80 g of material sieved to 63 µm was analysed depending on the quantity of sediment available, and the measured activities were decay-corrected to the sampling date. Counting efficiencies and reliability were conducted using certified International Atomic Energy Agency (IAEA) standards (IAEA-444, 135, 375, RGU-1 and RGTh-1) prepared in containers identical to those used for the samples.

## Modelling approach

Fallout radionuclide activities ($^{7}$Be, $^{210}$Pb$_{xs}$, $^{137}$Cs) may be used to distinguish between the contributions of four contrasted sources in each sediment sample (Table 2): re-suspended surface and subsurface material and recently eroded surface and subsurface material. The source database from the upper Seine Basin is described in Le Gall et al. (2018). Due to their differing half-lives (54 days for $^{7}$Be, 22 years for $^{210}$Pb and 30 years for $^{137}$Cs) and fallout chronology ($^{7}$Be and $^{210}$Pb are continuously supplied by rainfall, whereas $^{137}$Cs was only supplied during atmospheric tests in the 1960s and after the Chernobyl accident in 1986), surface sources (i.e. topsoil from agricultural land or urban parks) are considered to be enriched in $^{137}$Cs compared to subsurface sources (i.e., gullies, channel banks)(Evrard et al., 2020). Furthermore, particles that have been recently eroded are labelled with $^{7}$Be by rainfall during the erosion episode, while particles that were stored in the river channel and then remobilised during the flood are depleted in $^{7}$Be (Evrard et al., 2016) due to the lack of tagging by rainfall. An un-mixing model (Evrard et al., 2016) was used to estimate the relative contributions of these four sources to each target sediment sample collected during the three sampling campaigns.

## Results and discussion

All the data analysed in the current research is available on Zenodo (https://doi.org/10.5281/zenodo.16948966).

## Fallout radionuclide activities and sources of sediment

Fallout radionuclide activities varied significantly in the deposits collected during the three floods investigated, reflecting changes in the main type of material transported by the river. $^{137}$Cs activity levels were highest during the 2016 flood (mean: 4.3 Bq kg$^{-1}$; range: 2.5–5.2 Bq kg$^{-1}$), and lowest during the 2020 event (mean: 1.8 Bq kg$^{-1}$; range: 0.6–3.5 Bq kg$^{-1}$). Intermediate values for $^{137}$Cs were obtained for the most recent

<table><caption>**Table 2**
Table showing the contrasting activities in fallout radionuclides ($^{7}$Be, $^{210}$Pb$_{xs}$, $^{137}$Cs) in the modelled sediment source contributions.</caption><thead><tr><th rowspan="2">Material type</th><th colspan="3">Fallout radionuclide concentration</th></tr><tr><th>Be-7</th><th>Cs-137</th><th>Pb-210</th></tr></thead><tbody><tr><td>Old subsurface</td><td>Depleted</td><td>Depleted</td><td>Depleted</td></tr><tr><td>Old surface</td><td>Depleted</td><td>Enriched</td><td>Medium</td></tr><tr><td>Recent subsurface</td><td>Enriched</td><td>Depleted</td><td>Medium</td></tr><tr><td>Recent surface</td><td>Enriched</td><td>Enriched</td><td>Enriched</td></tr></tbody></table>

flood in 2021 (mean: 2.9 Bq kg$^{-1}$; range: 1.7–4.9 Bq kg$^{-1}$). These variations suggest that the sediment deposited during these events consisted of different mixtures of surface material (enriched in $^{137}$Cs) and subsoil (depleted in $^{137}$Cs). The three floods investigated exhibited relatively stable $^{210}$Pb$_{xs}$ activities, with mean values of 49 Bq kg$^{-1}$ (2016), 43 Bq kg$^{-1}$ (2020) and 48 Bq kg$^{-1}$ (2021), respectively. This stability in $^{210}$Pb$_{xs}$ activities is likely due to the continuous supply of this radionuclide through precipitation and its relatively homogeneous tagging of sediment over the medium term. Regarding the $^{7}$Be tagging of sediment, material deposited during the floods that took place in 2016 (mean: 124 Bq kg$^{-1}$) and 2020 (mean: 148 Bq kg$^{-1}$) was found to be enriched in this radionuclide, compared to material deposited in 2021 (mean: 62 Bq kg$^{-1}$). This differentiated tagging of sediment with short-lived $^{7}$Be likely reflects the more rapid transfer of eroded material in the river system in 2016 and 2020, compared to 2021.

Based on the contrasting fallout radionuclide activities observed, the model calculated very different sediment source contributions between campaigns (Fig. 2). During the 2016 flood, the main source of sediment was recently eroded surface material (43 ± 14 %). Conversely, older resuspended subsurface material was the main sediment source during the 2020 event (62 ± 28 %) and, to a lesser extent, during the 2021 flood (49 ± 22 %). These differences in sediment source contributions can be explained by floods triggered by different rainfall conditions. These different genesis mechanisms explain why different types of material were mobilized preferentially. In 2016, the flood occurred in June, in response to a heavy storm after a very rainy spring. Therefore, saturated soils led to intense runoff and erosion of surface soils (Le Gall et al., 2018). In 2020 and 2021, the floods occurred in March and February, respectively, and were caused by winter rainfall. This was less intense than the spring storm in 2016, but occurred over a longer period. These winter rainfall episodes led to runoff, but were not intense enough to cause extensive erosion connected to the river. Conversely, the increase in water level led to the resuspension of older subsurface sediments that were stored in the channel as well as significant erosion of the channel banks.

## Total organic matter composition

The carbonate-free <63 µm size fractions of flood sediment deposits collected in 2016, 2020 and 2021 display a low scattering pattern for TOC concentrations (Fig. A2) at all deposition sites (average ± standard deviation – SD: 3.5 ± 1.4 %, range: 1.8 to 5.8 %), TN concentrations (0.32 ± 0.12 %, range: 0.17 to 0.56 %, with one outlier at 0.07 %), $\delta^{13}$C (–28.4 ± 0.5 ‰, range: –27.0 to –29.7 ‰) and $\delta^{15}$N (6.9 ± 0.6 ‰, range: 6.2 to 6.8 ‰). As the carbonate minerals were removed by acid treatment, the TN concentrations, as determined by a ponderal method, increased slightly (by an average of 0.03 %). Some leaching of labile organic matter occurred, resulting in an average $\delta^{15}$N shift of 0.5 ‰, close to the analytical uncertainty of 0.3 ‰. The low TOC:TN ratios, ranging from 9.2 to 12.3 with an average of 11.1 ± 0.9), and the high $\delta^{15}$N values are typical of mineral-bound organic matter in soil-derived sediments, and correspond to soil organic matter with ratios of around 10 and enriched $^{15}$N isotopic values (Huon et al., 2018). The $^{13}$C-depleted values correspond to soil organic matter derived from C3 photosynthetic plants, which provide the main vegetation cover in the upper catchment. However, these values do not allow any further source discrimination. Due to possible overlaps in source organic matter signatures (Lamb et al., 2006), a minor contribution of aquatic biomass cannot be excluded. No evident correlation between TOC or TN concentration values vs. $\delta^{13}$C or $\delta^{15}$N that could discriminate between contrasting soil-derived sources of sediment mixed during transport and deposition has been identified (Laceby et al., 2016). Accordingly, the composition of the fine sedimentary organic matter was found to be homogenous along the Seine River in Paris, likely reflecting an “average” organic matter signature of the contributing soil-derived sources in the upper catchment.
<figure><img src="image_4.png" /><figcaption>**Fig. 2.** Sediment source contributions (%) in flood sediment deposits collected during the flood events investigated in 2016, 2020 and 2021 along the Seine River within Paris City.</figcaption></figure>

Metal concentrations, composition and enrichment factors (EF)

Elemental concentrations for 24 elements including Al, Ca, Cu, Zn, Ag, Sb and Pb and the values of enrichment factors (EF) are provided in the Zenodo dataset. The covariance compositional biplot and centered log-ratio transformed data were used to explore this data (Figure A3). The first two principal components explained 57 % of the total variance.

As Figure A3 shows, samples collected in 2016 exhibited fewer compositional variations than samples collected in 2020 and 2021, and are constrained within a smaller area of the plot. In contrast, samples collected in 2020 and 2021 exhibited greater variations. The most significant compositional variation in the sediment can be explained by the loads of Sb, Mo, Pb, Cu and Zn on the first component axis and positively correlated, and by Ag on the second. Elements on the first axis (Sb, Mo,

<figure><img src="image_5.png" /><figcaption>**Fig. 3.** Metal enrichment factor in sediment flood deposits collected during the 2016 (Le Gall et al., 2018), 2020 and 2021 floods. Sample locations are given in distance from Pont de Tolbiac (in meters).</figcaption></figure>
Pb, Cu and Zn) are found in high concentrations in most samples collected in 2020 and in one sample collected in 2021. Two samples collected in 2021 are highly enriched in Ag compared to the other samples. Upstream samples (in yellow) are generally depleted in Sb, Mo, Pb, Cu and Zn, except for two upstream samples collected in 2020.

The elemental concentrations vary considerably from one flood to the next, and from one site to another. To capture the spatial and temporal trends, the contamination will be discussed in more detail based on the enrichment factors. Flood sediment deposits collected during the 2020 flood were more enriched in metals than those samples collected in 2016 and 2021 (Fig. 3 and Figure A3). The enrichment factors show a significant increase during the 2020 flood, followed by a gradual return to 2016 levels during the 2021 flood. This general observation can be related to the transport of material originating from contrasting sources during the three floods. In 2020, the transported sediment was mainly composed of re-suspended subsurface material. This resuspension of older sediment during the flood has likely led to the flushing of ancient metal contamination stored in the channel or in its close vicinity. In 2021, there was a decrease in the contribution of old subsurface material, alongside a general decrease in metal enrichment. The sample collected near the Eiffel Tower in 2021 showed high levels of metal enrichment, including Cu (~9), Zn (6) and Pb (~8) (Fig. 3). This may be related to the ongoing restoration of the monument's paintwork.

Lead isotope ratio, sediment sources and Notre-Dame signature

Before the Notre-Dame Cathedral Fire in 2019, anthropogenic Pb sources in Paris included the widespread Pb present in the Parisian area, which is often referred to as ‘urban’ lead (²⁰⁶Pb/²⁰⁷Pb ~1.155) and the Pb used intensively during the Haussmann reconstruction of Paris (Ayrault et al., 2012). The latter, known as ‘historical’ lead, is characterized by a ²⁰⁶Pb/²⁰⁷Pb ratio ranging from 1.163 ± 0.003 to 1.166 ± 0.003 (Ayrault et al., 2014a). An input of Pb from gasoline additives was also found during the second half of the 20th century, culminating in 1986 as shown by Seine River sediment core records (Ayrault et al., 2012). Although this third source of Pb may still be present in street dust, it has been found to have decreased to negligible levels in the Seine River sediment in the early 2000s (Ayrault et al., 2014a). The Notre-Dame Cathedral Fire in April 2019 was then potentially expected to supply an additional source of Pb. Based on fire dust collection (Briard et al., 2023), the ²⁰⁶Pb/²⁰⁷Pb signature of these emissions was estimated to vary between 1.1669–1.1685 (average: 1.1676 ± 0.0006). Le Roux et al. (2023) determined a very similar Pb isotope signature (²⁰⁶Pb/²⁰⁷Pb = 1.1697 ± 1.10⁻⁵) in particles from the fire plume sampled at Le Vésinet (~15 km west of Paris, in the main fire plume). Therefore, the Notre-Dame fire signature is significantly distinct from the aforementioned urban signature, although it remains close to the historical Pb signature, which makes it difficult to distinguish

<figure><img src="image_6.png" /><figcaption>**Fig. 4.** Variations in ²⁰⁶Pb/²⁰⁷Pb signatures in sediment flood deposits collected during the 2016, 2020 and 2021 floods, compared to those of potential sources, over the 1/ER ratio. Upper panel: distance of sediment samples from 'Pont de Tolbiac' bridge in downstream direction. Lower panel: distribution of the sediment samples according to the sampling campaign.</figcaption></figure>
unambiguously both sources of Pb.

The Pb isotopic signature of sediment collected after the 2016 flood shows relatively low scatter (with $^{206}\text{Pb}/^{207}\text{Pb}$ values comprised between 1.169–1.175) compared to the larger dispersion of values found in 2020 (range: 1.152–1.177) and 2021 (range: 1.157–1.187). Overall, the $^{206}\text{Pb}/^{207}\text{Pb}$ ratios in samples collected in 2016 are closer to the Notre-Dame fire signature (Fig. 4) than in most samples collected in 2020 and 2021. However, when combining the examination of several Pb isotope ratios (i.e., $^{206}\text{Pb}/^{207}\text{Pb}$ vs. $^{208}\text{Pb}/^{206}\text{Pb}$), a clear distinction can be made between the signature attributed to Notre-Dame fire and that of the 2016 flood sediment (Fig. 5). This observation highlights the need to combine several indicators when using the Pb isotope ratios for investigating potential sources of contamination to avoid drawing potential misleading conclusions (Briard et al., 2024).

Interestingly, the sediment collected during the floods of 2020 and 2021 showed much more heterogeneous signatures than the material collected in 2016, which is consistent with the results of the compositional biplot analysis (Figure A3). Indeed, the 2020 sediment signature covered a wide range of variations of lead isotope ratio ($^{206}\text{Pb}/^{207}\text{Pb}$:

1.152 – 1.177) and elemental composition (Figure A3). Samples collected downstream of Notre-Dame (at Pont Neuf, Musée d'Orsay and Eiffel Tower) in 2020 have signatures that coincide with the expected Notre-Dame fire signature (Fig. 5). This may be attributed to Pb fallout and/or transport with runoff that may have occurred shortly after the fire. Most probably, this proximity is due to an unfortunate coincidence. Indeed, regardless of the year, samples of Seine floodplain sediment are plotting along a mixing line between Pb gasoline additives ($^{206}\text{Pb}/^{207}\text{Pb}$: 1.08–1.11; Véron et al. (1999)) at one end and the Seine River Pb geochemical background at the other ($^{206}\text{Pb}/^{207}\text{Pb}$: 1.201; Elbaz-Poulichet et al. (1986)). In contrast, the Pb ratios of the 2020 flood sediment are close to the urban Pb signature (Fig. 5). This is corroborated by the sediment's higher enrichment in other urban metals (e.g. Cu, Zn; Fig. 3).

The sediment material collected in 2021 showed even more heterogeneous characteristics. Most of the samples had $^{206}\text{Pb}/^{207}\text{Pb}$ signatures comprised between 1.156 and 1.187. Additionally, only the sample collected at Pont-Saint-Michel exhibited values (1.167 ± 0.006) that coincided with the Notre-Dame signature. Accordingly, these results did not highlight any widespread impact of the cathedral reconstruction

<figure><img src="image_7.png" /><figcaption>Fig. 5. Lead isotopic signatures ($^{206}\text{Pb}/^{207}\text{Pb}$ against $^{208}\text{Pb}/^{206}\text{Pb}$) of potential Pb sources in Paris and corresponding values found in sediment samples collected during the 2016, 2020 and 2021 flood events. Upper panel: distance of sediment samples from 'Pont de Tolbiac' bridge in downstream direction. Lower panel: distribution of the sediment samples according to the sampling campaign. Sediment from Bouafles and Muids were collected along a Seine River section downstream of Paris.</figcaption></figure>
works on the further dissemination of Pb contamination. Instead, the signatures of the 2021 flood sediments demonstrate a relatively high contribution from the natural Pb background (Fig. 5).

Among the samples collected in 2021, two samples showed distinct low $^{206}$Pb/$^{207}$Pb signatures. These were collected near the Pont-de-la-Tournelle and the Eiffel Tower. In the latter case, this distinct signature is most likely due to the ongoing repainting of the monument. However, the signature (1.157) of this sample differs significantly from that of the street dust collected near the Tower in 1997 (1.174), instead being similar to the signature of dust collected from other Parisian streets (1.151) during the same period (Nageotte and Day, 1998). Furthermore, this sediment's signature coincides with the so-called Pb 'urban signature' (Ayrault et al., 2012). This suggests that the high concentrations of Pb, Cu, Zn, As, Ag and Sb recorded at the Eiffel Tower (Figure A3) in 2021 may be due to runoff from nearby streets rather than the ongoing painting works.

## Sources and contamination of sediment

Overall, the sediment deposits collected in 2016 contained a higher proportion of upland surface sources (70±17 %) than those sampled in 2020 (19±14 %) and 2021 (33±15 %). Consequently, the material collected in 2016 was therefore found to be less contaminated in Pb, and characterised by a $^{206}$Pb/$^{207}$Pb signature of ~1.18. This signature has been widely found in agricultural soils in the Paris Region and has been attributed to coal combustion. Half of the Pb deposits in these soils are expected to have occurred prior to 1928 when coal was the dominant fuel (Semlali et al., 2004). Upland soils have the potential to retain an imprint of ancient contamination for extended periods (e.g. up to 1840 years for PAHs stored in an upstream subcatchment of the Seine Basin) (Gateuille et al., 2014). The flood that occurred in 2016 transported ~50 % of recently eroded sediment and a similar proportion of remobilized material (Le Gall et al., 2018). In contrast, samples from 2020 to 2021 mainly consisted (on average: 71–73 %) of remobilized material. This likely explains why samples collected during both years exhibited much more heterogeneous Pb contamination levels and sources than those from 2016. In 2020, the samples showing the most pronounced urban signature were modelled to originate almost exclusively from 'old sub-surface material' and were all found in the vicinity of the *Île-de-la-Cité* where Notre-Dame is located (with the exception of the samples collected in Austerlitz). However, this pattern is no longer observed in 2021 with the two most urban outliers found near the Pont de la Tournelle and the Eiffel Tower. These results demonstrate the strong impact of local contamination sources such as street dust and historical monuments on Pb contamination of Seine River sediment during medium floods (i.e., those of 2020 and 2021). Conversely, during periods of extreme flooding (e.g., 2016), material from upper catchment areas will provide the primary source of sediment. The results also demonstrate the rapid turnover of sediment in the absence of large deposition areas across Paris City as the contamination levels and signatures vary significantly from one flood to the next. This result is consistent with previous estimations of sediment residence times in the Seine River (115–307 days) as modelled based on their fallout radionuclide activities (Le Cloarec et al., 2007). Overall, these results emphasize that the Pb signature overlap of different sources complicates the unambiguous attribution of Pb contamination origin and highlights the limitations of relying on isotopic tools alone in this context.

## Conclusions

In recent years, several flooding events have resulted in significant overflow and sediment deposition on the quays of the Seine River across Paris, France. The sediment was found to originate from a variety of sources, depending on the event and the rainfall conditions that triggered it. Multi-proxy sediment fingerprinting is essential for disentangling local urban Pb sources from exceptional contamination events.

The current research suggests that the Notre-Dame Cathedral Fire had a very limited impact of on Pb contamination in Paris, likely due to the relatively small quantity of Pb emitted by the fire compared to the large and widespread sources of Pb found across the city, and its monuments and infrastructures. In the future, sediment in the Seine River in Paris should continue to be monitored, especially in the context of the reopening of bathing sites in the river to the general public from July 2025 onwards.

## Funding

This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

## CRediT authorship contribution statement

**Olivier Evrard:** Writing – original draft, Supervision, Methodology, Investigation, Funding acquisition, Formal analysis, Data curation, Conceptualization. **Rémi Bizeul:** Writing – review & editing, Visualization, Methodology, Investigation, Formal analysis, Data curation. **Yangjunjie Xu-Yang:** Writing – review & editing, Investigation, Data curation. **Sylvain Huon:** Writing – review & editing, Investigation, Formal analysis. **Laurence Le Callonnec:** Writing – review & editing, Investigation, Formal analysis. **Anthony Foucher:** Writing – review & editing, Visualization, Investigation. **Sophie Ayrault:** Writing – review & editing, Supervision, Methodology, Investigation, Funding acquisition, Formal analysis, Conceptualization.

## Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

## Acknowledgements

This work was made possible thanks to the financial support of the PIREN-Seine programme, the Chantier Scientifique Notre-Dame (CNRS/ INEE, Ministry of Culture) and the INTERPOL project (INTERcomparison of sediment POLLution on the main French rivers), which was funded by OFB (French Agency for Biodiversity). The authors are also grateful to Louise Bordier and Justine Briard for their contribution to geochemical analyses, to Irène Lefèvre for gamma spectrometry analyses and to our late friend and colleague Prof. Matthieu Roy-Barman for his previous work and collaboration on the Pb contamination in the Seine basin.

## Supplementary materials

Supplementary material associated with this article can be found, in the online version, at doi:10.1016/j.hazadv.2026.101072.

## Data availability

Data has already been uploaded on Zenodo and is accessible in open access.

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