Assessment of the water quality of the Ruisseau des Marais

In the Ruisseau des Marais stream in the canton of Geneva, an unexplained decline in the brown trout and minnow populations was observed in autumn 2022. Potential causes include rainwater overflows, contaminated sites, pesticides and contamination with nonylphenol. Chemical analyses revealed contamination with the insecticide pirimicarb, the drug azithromycin, copper, zinc and nitrate. In order to determine possible toxicity to fish or their food, macrozoobenthos and biofilms, the ecotoxicological water and sediment quality in the Ruisseau des Marais is determined using biotests and biomarkers. The following test systems are used:

Effects on vertebrates

• CALUX® panel (Cytotox-, PXR-, Nrf2-, ER-, anti-AR-, and PAH-CALUX®) for the evaluation of cytotoxicity, pollutant metabolism, oxidative stress, oestrogenic and anti-androgenic activity, cell response to PAH (Biodetection Systems)
• Toxicity on gill cells of rainbow trout (RTgill-W1)
• Measurement of molecular biomarkers in brown trout

Macrozoobenthos

• Effects on mortality, reproduction, feeding behaviour and neurotoxicity of freshwater amphipods (Gammarus fossarum)
• Sediment contact test with ostracods (Heterocypris incongruens)
• Chronic toxicity to midge larvae (Chironomus riparius)
• Analysis of the species community of oligochaetes (genetic oligochaete index)

Biofilms

• Combined algae test with unicellular green algae: Effects on photosynthesis and growth
• Luminescent bacteria test: non-specific toxicity, demonstrated by effects on energy metabolism