Bioavailability and toxicity of micropollutant mixtures to freshwater microalgae
In natural waters, aquatic organisms are exposed to numerous inorganic and organic micropollutants (defined as synthetic and natural trace contaminants present in water at low to very low concentrations, from pg/liter to ng/liter).
Metals (inorganic micropollutants) are natural components of aquatic systems and some of them are essential for life. However, human need for energy (e.g., burning of fossil fuels) and minerals (e.g., smelting of metallic ores) provoke an increase in the concentrations of essential metals, but also of toxic ones such as cadmium, mercury or lead. All metals can be considered toxic at relatively high concentrations. Organic micropollutants, which are almost exclusively man-made, are also present in natural waters. Their sources are diverse, from discharge of wastewaters and industrial installations to pesticide runoff water from agricultural lands. Aquatic organisms are thus exposed to a mixture of numerous contaminants originating from industrial, agricultural and domestic activities. In response to the increasing amounts of various micropollutants entering the environment, international ambient water quality guidelines have been established to protect aquatic organisms from their adverse effects. In most cases, the water quality standards are defined as the concentration (e.g., of dissolved metals) in natural waters above which ecological damage can be expected. However, these guidelines are mostly derived from single-species toxicity data of one individual chemical compound, merely testing exposure to one toxicant at a time and rarely to toxicant mixtures. The present project aims to fill this gap with the study of the interactions between metals and organic compounds at the biochemical and physiological level in the unicellular green alga Chlamydomonas reinhardtii, a representative aquatic microorganism.
Three key questions are addressed: (i) How do organic micropollutants modify metal uptake by microorganisms? (ii) Do organic micropollutants change the intracellular fate of metals? and (iii) To what extent does the impact of organic micropollutant on metal accumulation and intracellular distribution induce toxicity in microorganisms?
The project contributes to a more profound comprehension of mixture stressor effects on natural communities with the aim to enable a more realistic and reliable risk assessment for natural waters.