Effects of polyethylene-type microplastics on the growth and primary production of the freshwater phytoplankton species Scenedesmus armatus and Microcystis aeruginosa

[Display omitted] •28-days PE-MP exposure alters the cell growth of freshwater primary producers.•M. aeruginosa reversed the adverse effects of PE-MPs on cell growth after 3–7 days of exposure.•After 28 days of PE-MP exposure, primary producers exhibited decreased gross photosynthesis.•PE-MPs mainly altered the cell respiration of freshwater primary producers.•28-days PE-MP exposure decreased MC release without modifying MC synthesis. The ecological impacts of microplastic particles are primary environmental concerns. In this study, we selected three polyethylene particles (white, blue and fluorescent-blue microspheres, PE-MPs) and tested their effects on the growth and photosynthetic activity of the green algae Scenedesmus armatus and the cyanobacterium Microcystis aeruginosa after 28 days of exposure to 250, 500 and 1000 μg mL−1 concentrations. The white or fluorescent blue microspheres induced significant decrease on S. armatus cell growth in a concentration- and time-dependent manner, while blue microspheres did not induce significant differences in cell growth relative to that in the control. Although the M. aeruginosa strain initially underwent a reduction in exponential growth, the growth was able to recover and reach the value in the control group after the seventh day of exposure. In the same way, the three polyethylene-type microspheres had the ability to alter the photosynthetic activity of the S. armatus and M. aeruginosa strains after 28 days of exposure, mainly altering between 50–85 % of the light respiration depending on the strain and type of microplastic. Additionally, in all cases, microcystin release from M. aeruginosa after 28 days of exposure showed a moderate reduction of approximately 15 % compared to that in the control group, without the cellular synthesis of microcystin being altered. The interspecies differences in the magnitude of the effect produced by each type of microplastic highlight the need for further research on different chemical PE-MP compositions with additional test organisms to comprehensively understand MP pollution in aquatic-exposed organisms.