Sub-lethal effects of nanoplastics upon chronic exposure to Daphnia magna

Studies of microplastic and nanoplastic toxicity on aquatic invertebrates predominantly focus on short-term effects such as mortality and immobility. This study investigated sublethal effects on Daphnia magna when exposed to dialyzed 20 nm and 200 nm carboxylated polystyrene nanoplastics for 21 days. The study tested the effects of 50 mg/L of both particle sizes and 0.1 mg/L of the 20 nm particles. Data results between the 50 mg/L for both particle sizes, which maintains the particle mass concentration constant, and between the 50 mg/L 200 nm and 0.1 mg/L 20 nm treatments, which maintains particle number concentration constant, allowed comparison of dose metrics. Exposures of Daphnia magna to 0.1 mg/L and 50 mg/L of 20 nm particles enabled the evaluation of the effects of particle mass concentration on the toxicity of the smaller particles. Chronic exposure to polystyrene nanoplastics impacted growth, molting and reproduction of Daphnia magna at both tested sizes, and at particle concentrations as low as 0.1 mg/L. Overall, the results of this study showed similar trends in several measured endpoints whether using the mass concentration or particle counts as dose metrics and change in particle concentration did not result in a significant difference in the observed endpoints for 20 nm particles.