Interaction of High-Density Polyethylene Microplastics with Freshwater Microalgae Chlorella vulgaris and Scenedesmus quadricauda

The objective of the present study was to evaluate the impact of high-density polyethylene (HDPE) used in two particle sizes (40 and 125 µm) on selected biochemical parameters in two species of green algae: Chlorella vulgaris and Scenedesmus quadricauda. Exposure to microplastics resulted in decreased cell numbers (up to 43%) and reductions in protein (up to 42%), monosaccharide, and chlorophyll contents in both algal species. Oxidative stress, as reflected by increased hydrogen peroxide levels (up to 120%) and enhanced lipid peroxidation, was observed in HDPE-treated cells. This was accompanied by elevated antioxidant enzyme activity, changes in ascorbate and proline content, and alterations in carotenoid composition. Thus, toxicity of HDPE and the induction of defense mechanisms involved in adaptation to environmental pollutants were confirmed in both microalgae. Changes in the physicochemical properties of the tested polymer surface were investigated using Fourier-Transform Infrared Spectroscopy, scanning electron microscopy (SEM), and porosimetry analysis. The presence of biofilm, hydroxyl groups, higher total pore volume, and maximum pore width on the surface of the microplastic confirmed that green algae may be responsible for the first step in HDPE structure modifications. Understanding the interactions between such micropollutants and green algae, key primary producers in aquatic food webs, is therefore essential.