Influence of the quality of dissolved organic matter on the toxicity of pesticides on micro-algae along a freshwater - marine water continuum (supervised by Soizic Morin of the IRSTEA Bordeaux in partnership with IFREMER Nantes and the UMR EPOC).
The likely impact of global change on the susceptibility of micro-algal communities to chemical contamination must be characterised to understand and grasp future vulnerability. This project proposes to extend the evaluation of toxic substance effects on phytoplankton communities to include their interaction with dissolved organic matter (DOM) for species from both types of major aquatic ecosystems: freshwater and marine water. Initially, the influence of the chemical variability of DOM on trapping toxic substances will be studied according to different sources and solar radiation to evaluate the influence of photo-degradation. Four species of micro-algae (freshwater and marine) will be cultured and exposed to various toxic substances, alone and mixed, with and without DOM collected in situ, and irradiated or not. Changes in growth, photosynthetic activity, pigment concentration, and the presence of oxidative stress will be studied based on these factors indicating foreseeable changes to aquatic environments. Species responses will be compared in terms of their origin (freshwater / marine) and lifestyle (planktonic and benthic). By performing these original experiments in controlled laboratory conditions using field material (MOD and some species of micro-algae), the project will determine whether interactions between chemical contaminants and DOM, including the effect of photo-degradation, have a significant impact on the toxicity of these contaminants in inland and coastal aquatic compartments. This project confirms the interest of considering "multi-stress" situations in ecotoxicological bioassays.