Luis et al. showed that synthesized PCL nanoparticles (mean diameter 329 nm) were acutely toxic to zebrafish embryos with LC50 of 168.9 µg/mL at 96 hpf. Based on these data in the literature, assuming the consumer-grade PCL pellets used in our study released comparable quantities of material, the estimated concentrations of potentially shed nanoplastics, small microplastics, and oligomers at the LC50 for consumer-grade PCL were ~50 µg/mL (~610 7 particles/mL), ~20 µg/mL, and ~10 µg/mL, respectively. The value of 50 µg/mL (~610 7 particles/mL) is comparable to the LC50 for PCL nanoparticles established by Luis et al. and is likely an underestimate because our exposure conditions were saltier and slightly more basic than those of Tamayo-Belda et al., which can increase PCL degradation. Additionally, nanoparticle biological activity generally increases with decreasing particle size, suggesting that the LC50