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Effect of microplastic particles on viability of the selected ciliated protozoa
Summary
Researchers exposed three species of freshwater ciliates to polystyrene microbeads (1 and 2 µm) at two concentrations and found species-specific, concentration-dependent effects on population growth and ingestion rates. Ciliates are a key component of the microbial food web, and their ingestion of microplastics means these particles can be transferred to higher trophic levels even through microscopic organisms. The variable responses across species underscore the need for multi-species assessments when evaluating microplastic ecotoxicity.
Abstract Microplastics (MPs) due to their microsize, which overlaps with the typical food size of various aquatic organisms, can be ingested and move up the food chain, accumulating in the bodies of organisms at higher trophic levels. Few studies have focused on the uptake of MPs by ciliates, which are an important element of the microbial cycle. Three different ciliate species were used in the study: Blepharisma japonicum, Euplotes sp. and Spirostomum teres, and two types of polystyrene beads with a diameters of 1 and 2 µm in two concentrations (106 and 107 beads × mL− 1). The results of the experiments showed that microplastics have a variable, species-specific effect on the population growth rate of ciliates, which is directly dependent on their density in the environment (p < 0.01). It was also observed that the number of MPs ingested changed over time, depending on their density and size. On average, the highest number of ingested MPs (883.11 ± 521.47) was recorded after 60 min exposure to a low concentration of smaller beads in B. japonicum. The lowest number of beads was observed after 5 min exposure to a low concentration of larger beads in the same species. The rate of uptake of MPs by ciliate species was significantly dependent on their density, exposure time and size (p < 0.001). The highest clearance rate was observed in ciliates shortly after the start of the experiments in the environment with the lowest density of MPs.