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

• Public concerns regarding metal contamination in Paris following Notre-Dame Fire • Sediment deposits collected after floods of the Seine River in 2016, 2020 and 2021 • Analysis of fallout radionuclides, elemental geochemistry and lead (Pb) isotopes • Pb contamination in sediment was the highest in 2020 after Notre Dame Fire • Notre Dame Fire is only a minor source of Pb compared to other urban sources 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.