Flood-induced mobilization of organic pollutants in Valencia after the 2024 DANA event: an integrated environmental risk assessment.

The occurrence and distribution of organic contaminants mobilized by the October 2024 cut-off low (DANA) event that severely affected the province of Valencia (Spain) were analyzed by use of LC-HRMS and GC-MS/MS. Extreme rainfall generated approximately over 800,000 tonnes of sludge, much of which was redistributed across urban and peri-urban areas or transported to sensitive ecosystems such as Albufera Natural Park. Sludge and dust were analyzed for a broad spectrum of legacy and emerging organic pollutants, including pesticides, legacy and emerging brominated flame retardants, short-chain chlorinated paraffins, plastic additives, and personal care products. All contaminant classes were detected in both matrices, with particularly high concentrations of phthalates and certain pesticides. Legacy compounds such as lindane, DDT metabolites, and PBDEs were frequently identified, indicating remobilization of historically contaminated sediments. Dust samples generally exhibited higher total contaminant loads than sludge, dominated by plasticizers (notably DEHP and DINP). Environmental risk was assessed using the hazard quotient (HQ) approach based on sediment PNECs. Several pesticides (e.g., cypermethrin, heptachlor epoxide, lindane) and plastic additives (notably DEHP) showed HQ values exceeding 1, with worst-case scenarios indicating substantial ecological risk. These estimates reflect a screening-level assessment and are subject to uncertainties in exposure and toxicity data, and should therefore be interpreted as indicators of potential risk. Considering the large volume of sludge generated, the event may have mobilized significant quantities of pollutants posing potential threats to downstream aquatic systems, although the magnitude cannot be fully determined without baseline data. While dust inhalation may represent a secondary human exposure pathway, current evidence suggests limited immediate public health risk. These findings underline the role of extreme climatic events as vectors of diffuse chemical contamination and underscore the need for integrated post-disaster environmental monitoring and risk management strategies.