Résumé
The ROCCHSED 2023 campaign analysed 140 historical (metals, PAHs, etc.) and emerging chemical contaminants (PBDEs, PFASs, etc.), as well as nitrogen, phosphorus and, for the first time, micro-plastics in surface sediments at around sixty points in 21 lagoons in Occitanie, Bouches-du-Rhône and Corsica. The study revealed marked chemical contamination of sediments in the Bolmon, Méjean-Pérols and La Peyrade lagoons, with an east-west contamination gradient for Thau lagoon, both for metals and organic contaminants. In contrast, Ayrolle, Leucate, Canet and Palu lagoons sediments have a good chemical quality for metals by 2023. Two areas appear to be more contaminated: ‘petit étang’ in Thau lagoon (metals, PCBs, PAHs, DDT and TBT) and at the arrival of the Lez river, impacted by inputs from Montpellier and Palavas towns (metals, DDT and PCBs). The central point of Berre lagoon and Bolmon lagoon are still very marked by industrial and urban contamination (PCBs, lindane metabolites, brominated flame retardants, phthalates) and Canet lagoon by the presence of DDT. The PFAS, newly measured in 2023, show contamination of the Vaccarès lagoon, the south of the Biguglia lagoon and the north of the Bages lagoon.. Since 1996, there has been a general decline in levels of sedimentary chemical contamination, except for nickel and copper, which have remained high overall since 2006. Some points remain contaminated with mercury and lead (in the Thau-Palavasiens complex), DDT (Canet and Prévost lagoons), or PAHs and PCBs (Canet, Leucate, Bages, Palu...) but without exceeding ecotoxicological thresholds. For nitrogen and phosphorus, 42% and 28% respectively of the stations are in good or very good condition. Points in the Ayrolle, Gruissan and Bolmon lagoons and most points in the Bages lagoon are in good or very good condition for both parameters, while those in Or, La Peyrade, Arnel, Prévost, Méjean, Thau (eastern stations) and Biguglia lagoons are in poor or mediocre condition. Compared with 2017, the situation in 2023 has deteriorated at the Palu (PT, NT and MO) and Urbino (PT and MO) points, and has improved for Bolmon (PT, NT and MO) and Gruissan (NT). The search for micro-plastics showed that the Corsican lagoons (Diana and Biguglia) seem to be the most affected by this problem.