As part of a multi-year scientific project, researchers have identified dozens of “contaminants of interest” scattered along the coastline of metropolitan France. This unprecedented inventory highlights the need to monitor these substances in marine environments to better protect ecosystems.
Studying the presence of chemical contaminants along the coastline
The French Office for Biodiversity (OFB) commissioned a broad study—the Emergent’Sea project—through a team of scientists from the National Centre for Scientific Research (CNRS), the French Institute for the Exploitation of the Sea (Ifremer), and the University of Bordeaux. The aim? To search for contaminants present in samples collected across the entire coastline of metropolitan France (from the Channel to the Mediterranean), mainly at sites affected by urban, industrial, agricultural, or port-related inputs. The final project report was published on the Archimer platform in March 2026.
To carry out their sampling, the researchers used passive samplers directly in the water, that is, non-biological devices capable of capturing contamination over a long period (26 monitoring sites). These samplers complemented a more traditional method, namely samples from molluscs (34 monitoring sites). According to the scientists, they were looking for no fewer than 102 organic substances and 21 metallic compounds.
“This project thus allowed, across the entire French coastline, the collection of data as homogeneous as possible: acquisition period, sampling, analyses, data processing.”, the report notes.
Identifying the most relevant substances to monitor
Following the analysis of the water samples, around 77% of the substances were detected, primarily herbicides (atrazine, metolachlor) and pharmaceutical residues such as paracetamol. In the mollusk samples, the bulk of contamination also came from herbicides but also from antifouling biocides (antifouling paints) used to prevent hulls from being covered by marine organisms. The results also demonstrated a notable presence of chemical contaminants (pesticides and medicines) in locations fairly distant from pollution sources and thus apparently preserved. The authors cite Ouessant Island off the coast of Brittany as an example.
For specialists, these are “contaminants of interest” that it would be wise to include in the French surveillance framework under the Water Framework Directive (WFD). A proposal to regard these substances as Specific Pollutants of Ecological Status (PSEE) is currently under evaluation. The aim of this proposal is to better assess the ecological state of coastal waters by identifying the most relevant components to monitor at the coastline. However, this is not a matter of health surveillance, since that responsibility largely lies with the Regional Health Agencies (ARS).
Moreover, the study demonstrated that pairing passive samplers with traditional mollusk monitoring helped optimize the surveillance of contaminants of interest. The project also revealed gaps in ecotoxicological thresholds that would effectively assess risks to marine ecosystems. Such thresholds are being determined, depending on the substances chosen as PSEE. In the meantime, the risks to marine ecosystems remain difficult to evaluate.
