Toxic Effects of Microplastics on Culture Scenedesmus quadricauda: Interactions between Microplastics and Algae

The number of microplastic particles in the environment is constantly increasing as a result of the decay of plastic waste, the incineration of which is associated with air emissions and the concentration of toxic combustion products in ash residues. Although numerous researchers have studied the effects of MPs on living organisms, only a small part of the published data is devoted to the study of the long-term toxic effects that MPs and combustion products of plastic have on phytoplankton organisms. The effect of different types of MPs and plastic incineration ash on the structural and functional growth parameters of a green microalga Scenedesmus quadricauda culture used as a test object was studied in a chronic experiment lasting 21 days. The development of the species was studied with the addition of five types of weathered MPs samples, obtained from macroplastics, collected in the supralittoral of the Barents Sea and one unweathered control sample at a concentration of 3 mg/L. In terms of changes in the number of Scenedesmus quadricauda cells, the following toxicity series was obtained in descending order: PU (polyurethane foam, weathered) > HDPE (food package, white, weathered) > HDPE (food package, red, weathered) > EPS (packaging material, weathered) > EPS (packaging material, unweathered) > PP (ship rope, weathered). In terms of the efficiency of photosynthesis (maximum quantum yield of PSII photochemistry (FV/FM)), polyurethane foam was found to be nontoxic, while other samples of MPs had a weak toxic effect. The effect of MPs on the culture caused a mosaic response, assessed by different parameters of the test object state: a strong inhibition of culture growth (with the addition of polyurethane foam) can be accompanied by a significant increase in thiobarbituric acid reactive substances (TBARS) in microalgal cells, while photosynthesis efficiency may not change. The toxicity of the residual ash obtained from the incineration of a mixture of weathered macroplastics was significantly higher than the toxicity of microplastics. Residual ash was studied at concentrations of 0.01, 0.1, 1, 10, 100, and 1000 mg/L and the toxicity was detected in terms of the change in the cell number only at a concentration of 1000 mg/L, at 0.01 mg/L in terms of the photosynthesis efficiency, and at 0.1 mg/L and above by the change in the amount of TBARS in microalgal cells.