Effects of chronic exposure to environmentally realistic microplastics on Daphnia magna: importance of particle size and morphology and implications for risk assessments.

Most ecotoxicity research with microplastics (MPs) in laboratories uses primary MPs, such as plastic microbeads. The present study aimed to determine the effects of three environmentally representative MPs: nylon and Kevlar microfibers and polystyrene cup fragments on Daphnia magna. The organisms were exposed to each MP type at five test concentrations (0.0064, 0.064, 0.25, 2.5, and 25 mg/L) for 21 days to investigate MP uptake and effects on survivorship, growth, and reproduction. Daphnia magna ingested all MP types and the uptake concentration increased logarithmically with exposure concentration. Microplastics did not significantly affect survival. However, reproduction was significantly reduced at high nylon microfibers concentrations (2.5 and 25 mg/L). Dry weights of D. magna were also significantly lower than the control when exposed to nylon microfibers at 0.064, 2.5, and 25 mg/L. Ingested MPs exhibited a strong and positive correlation with MPs concentration in water. Significant negative correlations were found between body size and ingested MPs and MPs in water of cup MP experiments. Particle size distribution analysis indicated a size-selective ingestion by D. magna. The effects of MPs on D. magna appeared to be influenced by particle size and surface morphology. Results of the present study are useful for ecological risk assessment for MPs. More studies across species are needed to further understand how MP type and uptake relate to biological effects, which is necessary for ecological risk assessment and management of MP pollution.