Diffuse and accidental industrial sources and fluxes of targeted and untargeted organic contaminants in rivers of an anthropized basin in France

Rouen, a densely populated city, is subject to anthropogenic pressure on its aquatic systems, resulting from both diffuse urban and industrial activities. In September 2019, a major fire at a chemical plant released 9500 tons of chemicals, generating a massive smoke plume. To assess its medium- and long-term impact on water bodies, sampling campaigns were carried out at three surface waters and two groundwater sites. Between 2021 and 2023, water and suspended particulate matter (SPM) were collected using passive samplers. Targeted analyses were performed to determine the concentrations and exported fluxes of selected regulated contaminants, including polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), and dioxins/furans. In parallel, untargeted analyses were conducted using chromatography coupled with high-resolution mass spectrometry (GC-HRMS, LC-HRMS) and ultra-high-resolution Fourier-transform ion cyclotron resonance mass spectrometry (FTICR-MS). Chromatogram reprocessing enabled the annotation of dozens of organic compounds, which were compared with an in-house database. The targeted analyses revealed a strong anthropogenic influence on surface and groundwater quality. The surface rivers located near the city center and the plant area were the most impacted, showing relatively elevated specific particulate PAH fluxes and the highest dioxin concentrations in SPM. But no direct causal link could be established between the targeted contaminants and the fire incident. In contrast, untargeted analyses identified non-regulated organic molecules potentially associated with the fire, in both dissolved and particulate phases, suggesting that the accident left a persistent chemical signature in the aquatic environment. SPM collected at sites closest to the plant exhibited the strongest presence of these potential fire markers.