Characterizing the effects of a complex contamination by pesticides: Preliminary results on the Cleurie River (France), a pilot site for an interdisciplinary approach based on phototrophic biofilms

In France, many rivers face complex cocktails of contaminants at concentrations sometimes close to environmental quality standards (EQS). This type of complex pollution is typically encountered in the case of pesticides, and is usually poorly reflected by the bioindicators currently implemented within the European Water Framework Directive (WFD). In fact these indicators are not always able to reveal the subtle effects of this type of pollution, i.e. direct episodic and chronic or indirect (via trophic transfer, etc.) effects. It is therefore essential to develop indicators able to detect early signs of changes in water quality under natural conditions, but also to assess the possible associated indirect effects (e.g. propagation of effects in the food chain, and from upstream to downstream) and their consequences on the functioning of ecosystems. For this purpose, phototrophic biofilms present a wide range of structural and functional descriptors that could be of interest. The contamination that has been observed for several years in the Cleurie River (Eastern France, Vosges) appears to be an ideal case study site for testing such descriptors. Due to industrial activities (textiles), this small headwater forested stream exhibit a complex cocktail of molecules, chronic and episodic (from daily to seasonal basis) but below EQS. This cocktail is characterized by high concentrations of glyphosate and AMPA as well as a high load of dissolved organic matter (OM) dominated by optical brighteners/dyes. The current media coverage of glyphosate associated to frequent changes in the color of the water feed a local environmental controversy, which is part of the more general and old one on the toxicity of pesticides. In this context, an in situ monitoring, solicited by stakeholders, has been recently initiated in order to identify global indicators allowing studying this contamination. Our objectives are to fingerprint the chemical signature of the toxic pressure (e.g. using integrative passive sampling and spectrometry) and to characterize its effects on biofilms, a pivotal ecological player in these ecosystems. This presentation will focus on the first results: traditional biofilm-based descriptors (primary production, biodiversity) will be compared to others currently under development, either structural (the occurrence of deformities displayed by diatoms) or functional (acquisition of tolerance to glyphosate via a PICT-Pollution Induced Community Tolerance approach). These results will be further used within the framework of a broader interdisciplinary approach aiming at studying the circulation of scientific knowledge between the different actors (researchers, end-users, stakeholders…) involved in this controversy.