Seasonal ice cover regulates the environmental fate and retention of nano-TiO2 in freshwater lakes.

Abstract

Seasonal ice cover alters aquatic physicochemical conditions, but its effects on engineered nanoparticle stability and retention in seasonally frozen lakes remain poorly understood. A combined experimental approach integrating in situ under-ice sampling and laboratory-scale ice-cover simulations were employed to investigate the environmental behavior of nano-TiO2. Scanning electron microscopy, X-ray diffraction, and Fourier-transform infrared spectroscopy were used to characterize particle aggregation, crystalline structure, and surface-bound species, respectively. Concentrations were (1.80 ± 0.06) × 106 particles L-1 in lake water and (1.75 ± 0.05) × 106 particles g-1 dry weight in surface sediments. Sediment-associated particles were smaller than those in the water column, indicating differences in particle size distributions between the two compartments. With increasing simulated ice thickness, the hydrodynamic diameter decreased from 605.37 ± 64.25 to 577.14 ± 58.76 nm, while the zeta potential shifted from -14.10 ± 5.80 to -17.32 ± 6.13 mV, consistent with enhanced colloidal stability and reduced apparent sedimentation. Dissolved organic carbon increased from 65 to 192.4 mg L-1 during ice-cover development. Further experiments showed that Ca2+ promoted aggregation more strongly than Mg2+ and Na+, whereas humic acid enhanced colloidal stability. FTIR and XPS analyses results suggested that dissolved organic matter interacted with nano-TiO2 through coordination and hydrogen bonding, while divalent cations promoted charge neutralization and have induced cation bridging. Overall, ice-cover related changes in dissolved organic matter and electrolyte composition influenced the balance between colloidal stabilization and aggregation, thereby affecting nano-TiO2 retention in the water column and transfer to sediments.

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