Table 2.

Grouping of MeOx ENMs and their bulk analogues based on dissolution results in water and DMEM (48 h of incubation, 100 mg/L initial concentration) using screening criteria from OECD ENV/JM/MONO (2015)44. Results from the current study (MnO₂, ZnO, CeO₂, Al₂O₃, Fe₂O₃) combined with results from Avramescu et al. [2020] (CuO, NiO, TiO₂). In blue are the ones that fall in a different category (“negligible”) at 24 h than at 48 h. Red boxes show nano falling in a different category than bulk (nd = not detected; <LOD = below the limit of detection); * 24 h results (48 h not available).

Media	Form (Initial Concentration)	MeOx	High (>70%)	Moderate (10–70%)	Low (1–10%)	Negligible (<1%)
Water	Nano (100 ppm)	ZnO			ZnO, 2.83% (2.28 mg/L)
		MnO2				MnO2, 0.03% (0.02 mg/L)
		CeO2			CeO2, 1.07% (0.87 mg/L)
		Al2O3			Al2O3, 1.38% (0.73 mg/L)
		Fe2O3				Fe2O3, <0.01% (<10 ug/L)
		CuO *				CuO, 0.99% (0.79 mg/L)
		NiO			NiO, 1.22% (0.96 mg/L)
		TiO2 *				TiO2, <0.01% (<10 ug/L)
	Bulk (100 ppm)	ZnO				ZnO, 0.87% (0.70 mg/L)
		MnO2				MnO2, 0.11% (0.08 mg/L)
		CeO2				CeO2, nd
		Al2O3				Al2O3, <0.01% (<10 ug/L)
		Fe2O3				Fe2O3, <LOD
		CuO *				CuO, 0.17% (0.19 mg/L)
		NiO				NiO, 0.05% (0.05 mg/L)
		TiO2 *				TiO2, <0.01% (<1 ug/L)
DMEM	Nano (100 ppm)	ZnO		ZnO, 19.3% (15.5 mg/L)
		MnO2			MnO2, 3.87% (2.44 mg/L)
		CeO2				CeO2, 0.42% (0.34 mg/L)
		Al2O3				Al2O3, 0.73% (0.39 mg/L)
		Fe2O3				Fe2O3, nd
		CuO		CuO, 51.5% (41.1 mg/L)
		NiO			NiO, 1.81% (1.42 mg/L)
		TiO2 *				TiO2, 0.04% (0.03 mg/L)
	Bulk (100 ppm)	ZnO		ZnO, 11.8% (9.8 mg/L)
		MnO2			MnO2, 1.37% (0.94 mg/L)
		CeO2				CeO2, nd
		Al2O3				Al2O3, 0.02% (0.01 mg/L)
		Fe2O3				Fe2O3, nd
		CuO			CuO, 1.51% (1.39 mg/L)
		NiO				NiO, 0.07% (0.06 mg/L)
		TiO2 *				TiO2, <0.01% (<1 ug/L)

* 24 h results (48 h not available).