Aggregation and ecotoxicity of CeO2 nanoparticles in synthetic and natural waters with variable pH, organic matter concentration and ionic strength

The influence of pH (6.0–9.0), natural organic matter (NOM) (0–10 mg C/L) and ionic strength (IS) (1.7–40 mM) on 14 nm CeO2 NP aggregation and ecotoxicity towards the alga Pseudokirchneriella subcapitata was assessed following a central composite design. Mean NP aggregate sizes ranged between 200 and 10000 nm. Increasing pH and IS enhanced aggregation, while increasing NOM decreased mean aggregate sizes. The 48 h-ErC20s ranged between 4.7 and 395.8 mg CeO2/L. An equation for predicting the 48 h-ErC20 (48 h-ErC20 = −1626.4 × (pH) + 109.45 × (pH)2 + 116.49 × ([NOM]) − 14.317 × (pH) × ([NOM]) + 6007.2) was developed. In a validation study with natural waters the predicted 48 h-ErC20 was a factor 1.08–2.57 lower compared to the experimental values.

Research highlights
► Algal ecotoxicity of CeO2 nanoparticles (NPs) depends on pH and NOM concentration.
► Increasing pH and ionic strength enhanced CeO2 nanoparticle aggregation.
► Increasing NOM concentration decreased mean CeO2 aggregate size.
► An empirical model to predict 48 h-ErC20 values of CeO2 NPs was developed.
► The model was validated using natural surface waters with various characteristics.