Toxicokinetics and Toxicodynamics of Nanoplastics in Daphnia magna are Polymer-Type Dependent

Diverse polymer types of nanoplastics (NPs) pose significant
ecological
risks in aquatic ecosystems. However, current research has largely
centered on polystyrene NPs (PS NPs), which constitute only a minor
portion of total NPs in freshwater environments. In this study, we
applied a toxicokinetic-toxicodynamic (TK-TD) modeling framework to
comparatively assess the accumulation, elimination, and toxicity of
four polymer types of NPs (PS, polyvinyl chloride [PVC], poly(methyl
methacrylate) [PMMA], and polycarbonate [PC]; all ∼ 80 nm)
in Daphnia magna. Aggregation-induced-emission fluorogen
labeling enabled precise tracking of NPs. Our findings revealed clear
polymer-type-dependent differences: D. magna accumulated
and eliminated PMMA and PC NPs more efficiently than PS and PVC NPs.
Toxicity followed the order: PS > PVC > PMMA > PC. Transcriptomic
analyses indicated that NPs disrupt nutrient digestion, oxidative
stress responses, and nervous system function. Using TK-TD modeling,
we further predicted the time-dependent median lethal concentrations
(LC50) and no-effect concentrations (NEC) for the NPs.
The 48-h LC50 values for PS, PVC, PMMA, and PC NPs were
15.0, 43.1, 66.5, and 389.7 mg L–1, respectively,
while the corresponding NECs were 4.5, 7.0, 13.5, and 60.0 mg L–1. Our study provides a comprehensive ecological risk
assessment of NPs from different polymer types, offering quantitative
thresholds to inform the development of polymer-specific water quality
criteria for NPs in aquatic environments.