Acute Toxic Effects and Toxicity-Source Analysis of CuO, ZnO, and SiO2 Nanoparticles in River–Lake Water Bodies

Engineered nano-metal oxides discharged into river–lake systems interact with water chemistry before reaching biota, yet the fraction of their acute toxicity that derives from the particles themselves, rather than from dissolved ions, remains unresolved in authentic natural waters. This study determined the acute toxic effects of CuO, ZnO, and SiO2 nanoparticles at a concentration of 100 mg/L dispersed in water samples from Taihu Lake and Suzhou River (two representative and polluted water bodies in eastern China) on Vibrio fischeri (V. fischeri), and partitioned each measured inhibition E(total) into an ion-attributed component E(ion) and a particle-attributed component E(particle) using paired assays of the whole suspension and of its 0.02 µm filtrate. Aggregation, surface charge, and dissolution kinetics were followed for 72 h (15 d for SiO2). CuO nanoparticles aggregated moderately in both natural waters and released at most 0.087 mg/L Cu2+, so that the persistent suspension inhibition of 0.09–0.64% coexisted with a mildly stimulatory ion fraction (−0.19% to 0.01%), leaving the particle component to account for 81.1–94.0% of the measured effect. ZnO nanoparticles released up to 7.15 mg/L Zn2+ in Suzhou River water, where inhibition rose in step with the dissolved fraction and the ion component contributed 56.8–95.6% of the effect; in Taihu Lake water, both the suspension and the ion fraction remained stimulatory. SiO2 nanoparticles and the released reactive silicate induced no acute inhibition over 15 d (mean −0.024% and −0.013% in the two waters, both significantly below zero) despite the net dissolution solubility reaching up to 32.4% of the nominal dose. The toxicity source therefore differs by material within the same water matrix, indicating that risk-management measures for CuO should target particle transport and settling, whereas measures for ZnO should suppress dissolution.