In the present study, the uptake and toxicity of two poly(methylmethacrylate)-based plastic nanoparticles (PNPs) with different surface chemistries (medium and hydrophobic) was assessed using aquatic organisms selected for their relevance based on the environmental behaviour of the PNPs. Pure poly(methylmethacrylate) (medium; PMMA) PNPs and poly(methylmethacrylate-co-stearylmethacrylate) copolymer (hydrophobic; PMMA-PSMA) PNPs of 86-125 nm were synthesised using a mini emulsion polymerisation method (Figure 1 A-B). Fluorescent analogues of each PNP (FPNPs) were also synthesised using monomer 7-[4-(trifluoromethyl)coumarin]acrylamide and studied (Figure 1 C-E). Daphnia magna, Corophium volutator and Vibrio fischeri were employed in a series of standard acute ecotoxicity tests, being exposed to the PNPs at three different environmentally realistic concentrations (0.01, 0.1, and 1.0 mg L-1) and a high concentration 500-1000 mg L-1. In addition, sublethal effects of PNPs in C. volutator were determined using a sediment reburial test whilst the uptake and depuration of FPNPs was studied in D. magna. The PNPs and FPNPs did not exhibit any observable toxicity at concentrations up to 500-1000 mg L-1 in any of the tests except for PMMA-PSMA PNPs and FPNPs following 48 h exposure to D. magna (EC50 values of 879 and 887 mg L-1, respectively). No significant differences were observed between labelled and non-labelled PNPs, indicating the suitability of using fluorescent labelling for tracing of the NPs. Significant uptake and rapid excretion of the FPNPs was observed in D. magna.