Interactive effect of nanoplastic particles and phototoxicant on microalgae

The purpose of the research was to study the combined effect of nanoparticles (NP) of pristine polystyrene and methylene blue (MB) on the cultures of phytoplankton organisms Scenedesmus quadricauda and Chlorella vulgaris (thermophilic strain). A series of experiments was conducted to study the combined effect of 100 nm NP of polystyrene at low concentrations of 10 and 50 mg l−1, in the presence of toxic concentrations 0.1 and 0.5 mg l−1 of MB on S. quadricauda and C. vulgaris. We used different approaches to quantitatively assess the toxicity of polystyrene NP and MB when they are present together in the algae cultivation medium. Synergistic, additive and antagonistic effects of MB and polystyrene NP paired combinations were shown depending on toxicants concentrations and duration of action. A decrease in the toxicity of the medium in a mixture of toxicants was observed for both cultures in terms of cell number. We attribute this decrease to the toxicants’ interaction with the type of antagonism towards all combinations of NP and MB for most observation periods. The efficiency of cell photosynthesis during the growth of the S. quadricauda culture was also investigated as a second criterion of the state of the culture during the experiment. Long-term effects of increased toxicity were found with the combined presence of 0.5 mg l−1 MB and 50 mg l−1 polystyrene NP, characterized by a synergistic type of their interaction. In contrast, binary combinations of their low concentrations of 0.1 mg l−1 MB and 10 mg l−1 polystyrene NP led to increased toxicity of the medium over time.