Effects of polystyrene microplastic particles on the morphological and functional parameters of Daphnia magna
Based on the results of laboratory modeling, the article evaluates the biological impact of microplastics on freshwater organisms using the example of the effect of polystyrene microparticles on the morphological and functional parameters (survival rate, size characteristics, locomotor and trophic activity) of freshwater crustaceans Daphnia magna Straus. The studied particles of polystyrene microplastics had homogeneous fractional composition in the experiments: < 10 µm (≈ 5%), < 50 µm (≈ 40%) and < 100 µm (≈ 75%). The median lethal concentration LC50 for polystyrene microparticles, determined in an acute toxicological experiment, was 197.35 mg/L (95% confidence interval: 163.10-259.98 mg/L). At 48 h of exposure in the entire range of the studied concentrations of microplastics (0 (control), 10, 50, 125 and 200 mg/L), no effect on the morphometric parameters of D. magna was found, the average size of individuals was 1.75±0.01 mm. After 24 h of exposure, the swimming speed of D. magna was maximal under control conditions (mean 0.87±0.10 cm/s). The addition of polystyrene microparticles into the medium at concentrations of 50, 125, and 200 mg/L significantly reduced (by about 44%) the swimming speed. The trophic activity of D. magna, estimated by the chlorophyll fluorescence of the alga Chlorella vulgaris Beijerinck and amounting to 96% under control conditions, decreased when microplastics were added to the medium, reaching 19% at the maximum concentration of microplastics (200 mg/L). It has been shown by microscopy that Chlorella cells that fill the gut of Daphnia under control conditions are replaced mainly by polystyrene particles when microplastics are added to the algae suspension at a concentration of 200 mg/L. The results obtained indicate the impact of polystyrene microplastic particles on freshwater organisms.