Polystyrene microplastics induce mortality through acute cell stress and inhibition of cholinergic activity in a brine shrimp

The environmental impacts of microplastics (MPs) are increasingly of concern, particularly for their sources, global distribution, and persistency in aquatic ecosystems. Although the ubiquitous and persistent nature of MPs in waterbodies is evident, their effects and health implications for aquatic animals are still open to debate. The brine shrimp, Artemia franciscana was exposed to different concentrations (1–1000 particles mL−1) of four sizes (1, 3, 6, and 10 μm) of non-functionalized polystyrene microbeads. To measure MPs effects, several physiological and biochemical parameters such as ingestion and egestion, stress biomarkers [e.g., heat shock protein 70 (hsp70) family, enzymatic activities of catalase (CAT) and superoxide dismutase (SOD)], acetylcholinesterase (AChE) activity, and survival rate for 30 days were analyzed. Exposure to waterborne MPs showed clear ingestion and egestion in A. franciscana. Exposure to relatively larger sizes of 1000 particles mL−1 MPs dose–dependently increased mRNA expression of hsp70 families and enzymatic activities of CAT and SOD within 96 h. Significant inhibitory effects on AChE activity were observed in response to 1000 particles mL−1 with increases in mortality for 30 days. Thirty-day survival of juveniles was dose-dependently affected, with greater effects seen at 1000 particles mL−1 of MPs. Our results suggest that MPs exposure to the early stages of brine shrimp could be detrimental for population maintenance through inhibition of cholinergic system and the induction of acute cell stress, including oxidative stress.