Employing spICP-MS to measure ingestion and uptake of a polydispersion of nano-microplastics in Daphnia magna and zebrafish embryo-larvae

Abstract

In the environment, plastics undergo chemical (weathering) and physical (abrasion) aging, forming vast polydispersions of irregularly shaped nano- (1–1000 nm) and microplastic (1000 nm–5 µm) particles (NMPs), complicating assessments of ingestion, uptake, and bioaccumulation of environmentally relevant NMP mixtures. Thus, we employed a novel cryomilling approach to produce metal-tagged (Ta), fluorescently dyed (Fl) non-spherical polymethyl methacrylate (PMMA) NMPs with environmentally realistic size distributions (~150–2,000 nm), that could be analyzed using single particle inductively coupled plasma quadrupole mass spectrometry (spICP-MS). This allowed for quantification of particle number across size range ingestion in individual Daphnia magna and zebrafish, representing both active (adult D. magna, zebrafish >6 days post-fertilization [dpf]) and passive (zebrafish 0–5 dpf) uptake routes. D. magna exposed to 50 and 0.5 µg/L Ta-Fl-PMMA for 24 h ingested an average of 66,420 and 850 particles per organism, predominantly <1 µm. Surprisingly, zebrafish embryos (0–5 dpf) showed no passive uptake, with or without their chorion intact. Similarly, no active ingestion or uptake was observed in zebrafish larvae (6–11 dpf) unless paramecia were introduced as a food source, resulting in an average ingestion of 204 particles at 50 µg/L Ta-Fl-PMMA. These findings demonstrate the effectiveness of metal-tagged NMPs and spICP-MS in quantifying NMP ingestion, and potential uptake in aquatic organisms at environmentally relevant particle number concentrations. Moreover, these results raise important questions about the mechanisms of NMP ingestion and potential uptake, indicating that there is limited passive uptake of particles >150 nm in early-life-stage zebrafish.