Microplastics pervade the hydrosphere and inevitably come into contact with aquatic organisms. The study reports quantitative data on absorption and excretion of polystyrene microspheres 2 and 10 µm in diameter by zooplankton and fish larvae on the example of Artemia salina L. and Acipenser rithenus L. At the initial concentration of 500 µg/L, A. salina accumulated 2 and 10 µm particles in amounts up to 0.103 and 0.151 ng/individual, respectively, at a similar rate. The mass content of large-sized particles in A. salina was significantly higher (p < 0.01) compared to small-sized particles throughout the experiment. Artemia salina and A. rithenus larvae did not accumulate microplastics in the gastrointestinal tract over a period of 96 and 72 h, respectively. Consumption of microplastics by A. ruthenus larvae with A. salina through the food chain was slower and less pronounced in mass than their direct absorption from water. The rates of absorption of 2 and 10 μm particles by fish attained 0.9 and 8.22 ng/individual/h from water, and 0.06 and 0.23 ng/individual/h with food, respectively. In the models of water pollution and food chain transfer, A. ruthenus larvae consumed more 10 µm particles in mass compared to 2 µm particles (p < 0.05) and at a higher rate. For 2 µm particles, the excretion time for 50% of particles from the gastrointestinal tract of fish (T50) was 32–33 h, whereas for 10 µm particles, the excretion of particles consumed with food was slower (T50=45 h) compared to that of particles absorbed directly from water (T50=25 h). The data obtained can be used to simulate transport and circulation of microplastics of different sizes in the environment.

Microplastics pervade the hydrosphere and inevitably come into contact with aquatic organisms. The study reports quantitative data on absorption and excretion of polystyrene microspheres 2 and 10 µm in diameter by zooplankton and fish larvae on the example of Artemia salina L. and Acipenser rithenus L. At the initial concentration of 500 µg/L, A. salina accumulated 2 and 10 µm particles in amounts up to 0.103 and 0.151 ng/individual, respectively, at a similar rate. The mass content of large-sized particles in A. salina was significantly higher (p &lt; 0.01) compared to small-sized particles throughout the experiment. Artemia salina and A. rithenus larvae did not accumulate microplastics in the gastrointestinal tract over a period of 96 and 72 h, respectively. Consumption of microplastics by A. ruthenus larvae with A. salina through the food chain was slower and less pronounced in mass than their direct absorption from water. The rates of absorption of 2 and 10 μm particles by fish attained 0.9 and 8.22 ng/individual/h from water, and 0.06 and 0.23 ng/individual/h with food, respectively. In the models of water pollution and food chain transfer, A. ruthenus larvae consumed more 10 µm particles in mass compared to 2 µm particles (p &lt; 0.05) and at a higher rate. For 2 µm particles, the excretion time for 50% of particles from the gastrointestinal tract of fish (T50) was 32–33 h, whereas for 10 µm particles, the excretion of particles consumed with food was slower (T50=45 h) compared to that of particles&nbsp;absorbed directly from water (T50=25 h). The data obtained can be used to simulate transport and circulation of microplastics of different sizes in the environment.