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

Microplastic pollution and its ecological impact on the aquatic environment are a current focus of research in the scientific community. These microplastics may adsorb contaminants discharged into the aquatic environment, thereby serving as a sink and source for the dissemination of these associated chemical contaminants. However, knowledge about the potential risks of microplastics and associated chemical contaminants on aquatic biota, especially on primary freshwater producers, remains to be explored. In this study, the impact of a polyethylene microplastic type (MP) associated with amoxicillin, ibuprofen, sertraline and simazine (OCs) on the cell growth and photosynthetic activity of the green algae Scenedesmus armatus and the cyanobacteria Microcystis aeruginosa was evaluated after 28 days of exposure. The results show that all the organic contaminants and their respective MP-OC complexes induced stress on cell growth after 28 days of exposure, except when the cyanobacterial strain was exposed to amoxicillin and ibuprofen. Similarly, photosynthetic activity was affected by exposure to MP-OC complexes, with the most evident effect on cellular respiration in the cyanobacterial strain and on net photosynthesis in the green algae strain. Additionally, the ability of the M. aeruginosa strain to synthesize microcystin was significantly reduced. These results show that the formation of MP-OC complexes could reduce their adverse effects, although there is wide variability depending on both the type of organic contaminant and the photosynthetic organisms involved, so further studies are needed to better understand the interactions between these aquatic contaminants.