ROCCH is the French monitoring network for the chemical contamination in coastal and transition water bodies. This network meets two objectives: assessing levels and trends of the chemical contamination of the French coastline and answering both environmental objectives of the Water Framework Directive (WFD) and obligations of marine regional conventions (OSPAR and Barcelona). For this purpose, bivalve mollusks are used as quantitative biological indicators for their properties to concentrate and accumulate pollutants in their soft tissues with a relationship to the ambient level; this characteristic makes the measurement of chemical contaminants technically simpler than in the water column. Furthermore, chemical monitoring in sediment is also performed. This sediment matrix remains also interesting for the monitoring of substances with significant accumulation potential.

In the Adour-Garonne district, extending from the Pertuis charentais to the Bidassoa estuary (Spain border), the chemistry monitoring on bivalves is performed on nine coastal and five transition (estuaries) water bodies. The chemical contamination of marine sediments is studied in six coastal and five transition water bodies.

According to different frequencies, the 25 hydrophobic and bioaccumulative substances of the WFD and OSPAR lists have been studied during the last decade. This poster presents the main results about chemical pollutants in the coastal and transition water bodies of the Adour-Garonne district, acquired in sediments and shellfish between 1999 and 2017.

Finally, in this district a good chemical quality of the coastal and transitional water bodies is observed, with nevertheless some critical sectors such as

• Gironde estuary, where the persistent Cadmium contamination in confirmed by the recent results;
• Arcachon Bay showing high concentrations of PAHs ;
• Bidassoa estuary, with high concentrations of TBT.

Thanks to these results, an assessment of the chemical quality of the Adour-Garonne coastline has been established and can be used to plan the environmental public policies.