Βραχυχρόνια έκθεση των μικροφυκών Scenedesmus rubescens και Dunaliella tertiolecta σε σφαιρίδια πολυστυρενίου

Environmental pollution with plastics is increasing in modern times. Excessive consumption of plastic products coupled with the problematic management of plastic waste results in the latter accumulating in the environment, posing a threat to biodiversity, with the seas being particularly burdened. The effect of small-sized plastic particles on aquatic organisms is considered to be quite alarming, and there is serious evidence that they are transported through the food chain to senior consumers. Particles smaller than 5 mm in size are called microplastics and their concentration in seas, lakes and rivers has been particularly high in recent years. The impact of microplastics on microalgae is of great importance for the whole aquatic ecosystem, as microalgae constitute the largest percentage of primary production in such an ecosystem, but also the basis of the food chain. At the same time, many micronutrients or derivatives are used by humans as food, drug ingredients, etc., and microbes are particularly important in wastewater treatment plants and in the production of biofuels. The present thesis investigates the effects of short-term exposure (72 or 96 h) to the freshwater microalgae Scenedesmus rubsecens and the marine microalgae Dunaliella tertiolecta on polystyrene beads. These beads are synthetic and fluorescent, and particles 28 and 160 nm in diameter, 0.6 and 1 µm were used, at concentrations of 10^4 to 10^10 particles / mL. The effect of their size and concentration of polystyrene beads on population growth and photosynthesis of the two species was studied (160 nm beads were used in the experiments to study photosynthesis). According to the results of the present work, polystyrene beads smaller than 1 µm in diameter, especially at high concentrations, are toxic to the growth of S. rubescesns and D. tertiolecta at least for a short period (72 to 96 h). The highest growth rate values ​​recorded were 1.221 d^-1 for Scenedesmus rubescens, which corresponds to day 2 control culture and 1.337 d^-1 for Dunaliella tertiolecta, which corresponds to day 2 control culture. For S. rubescens, the highest rate of inhibition of growth (88.89%) was observed in cultures exposed to 0.6 μm PS beads at concentrations of 10^5 and 10^6 particles / mL at day 2. For D. tertiolecta the corresponding percentage is 95.12%, in culture in the presence of 160 nm PS beads, at a concentration of 10^8 particles / mL.For inhibitory values ​​(IC50), for S. rubescens the lowest value corresponds to 5.37,10‧2 particles / mL (culture under exposure to 28 nm polystyrene beads at 48 h), whereas for D. tertiolecta the lowest value is 33.11 particles / mL (culture under exposure to 1 µm polystyrene beads at 48 h). For S. rubescens cultures the maximum chlorophyll a (4th day) concentration values ​​are: 647, 651 and 429 mg / m3 for the control culture and the 10^7 and 10^8 particle / mL PS concentrations, respectively (160 nm diameter). For D. tertiolecta cultures the corresponding values ​​are: 801, 706 and 536 mg / m3. It is further concluded that the size of the PS beads that were used, as well as the particular morphological characteristics of each microalgae, are important in the magnitude of the effects.