Chosing the caging sites
November 2025 saw a field prospecting campaign. Researchers from the ORION project criss-crossed the Meuse river basin to identify the most suitable sites for caging sentinel species in the Meuse, Sambre and Chiers rivers. This stage of exposing the animals to their natural environment will enable the assessment of bioaccumulated pollutant concentrations and their impact on the animals' health. Combined with concentration measurements taken directly in the water, these original tools will enable the assessment of water quality in the Meuse. We met with Mélissa Palos-Ladeiro (URCA), researcher and leader of the ORION project, and Omayma Missawi (UNamur), researcher in ecotoxicology, to answer our questions.
How were the sites initially identified? Based on what data?
The consortium pooled its expertise to identify sites of interest. It all started with the selection of the families of contaminants to be studied in the environment. The ISSeP (public laboratory) chose PFAS (forever chemicals), PAHs (harmful combustion products) and phthalates (toxic additives that make plastic flexible). This choice was influenced in particular by the environmental issues posed by these families, the technical possibilities for analysis and the ability of sentinel species to accumulate them in their tissues (bioaccumulation). ACTALIA (an agri-food institute) focused on selecting bathing sites with high microbiological pressures. The PEGIRE Unit at the University of Liège (water resource planning and management) produced maps, known as ‘pressure maps’, showing the most sensitive sites for studying the three families of pollutants selected for the project. These maps made it possible to identify a series of ‘candidate areas’ where active biomonitoring made the most sense: either because they are affected by known pollution or because they are subject to specific uses such as bathing, for example. Finally, teams from SEBIO (biomonitoring unit, URCA), URBE (environmental biology, UNamur) and INERIS (risk management) finalised the prospecting by considering the parameters of the sites and the organisms caged.
What additional parameters are involved in the choice of sites, beyond the data? (Such as tranquillity, distance from human traffic, etc.)
The maps give us an initial indication of areas of interest, but the final choice of sites is really decided in the field. The first criterion is always the welfare of the caged animals: we check the water depth, current speed, temperature, pH, oxygenation and sunlight to ensure that the animals can be caged there for three weeks with minimal stress. We also check the stability of the bottom and the possibility of securely anchoring the cages to prevent them from being torn away. Next come logistical and safety criteria, such as site accessibility, tranquillity to limit the risk of damage, and compatibility with other sentinel species, ideally located in the same area. In summary, prospecting serves to validate in the field that the sites proposed by the maps are truly suitable, safe and respectful of animal welfare.
What did the prospecting teach us about the potential sites?
Field prospecting confirmed that several sites identified using pressure maps were indeed suitable for caging, but it also revealed significant constraints that could only be anticipated through on-site visits. Some locations had insufficient water levels, while others had steep banks that prevented safe access and made it very difficult to anchor the cages. Thanks to these observations, the teams were able to adjust their strategy, select truly suitable locations, sometimes only a few metres from the initial points, and validate the final GPS coordinates for referencing the caging campaign.
Will each of the sentinel species be caged at all sites? If not, won't this skew the research results?
The sentinel species chosen for the project are complementary and will provide different levels of information depending on their capabilities (bioaccumulation rates, biological effects, etc.). In this sense, their simultaneous presence is not mandatory. However, there will be common periods for caging at all six study sites.
Which sites will ultimately be caged?
The team selected four river sites: on the Sambre in Jeumont and Floreffe, on the Meuse in Namur and on the Chiers in Sedan. Two recreational lakes on either side of the border will also be investigated: Lake Eau d'Heure in Belgium and a second lake on the French side, which has yet to be confirmed. The first French lake site chosen, Lac des Vieilles Forges, had been partially emptied on 1 September by EDF to supply the reservoir of a nearby hydroelectric power station, whose water had been used during the summer droughts. It was therefore necessary to choose another body of fresh water.
