Seasonal variability of natural water chemistry affects the fate and behaviour of silver nanoparticles

Understanding the environmental behaviour of nanoparticles (NPs) after release into aquatic systems is essential to predict the environmental implications of nanotechnology. Silver nanoparticles (AgNPs) represent a major class of engineered NPs with a significant potential for environmental impact. Therefore, investigating their transformations in natural waters will help predict their long term environmental fate and behaviour. AgNPs were characterized in natural lake water collected seasonally from the same freshwater source, using column microcosms to assess their behaviour and transport at different depths. Building on our previous work using similar systems with synthetic waters, the influence of water chemistry and NP surface modifications on colloidal stability and dissolution in natural lake water over time was investigated. A simple sedimentation-diffusion model parameterized by the particle properties and total Ag concentration was successfully used to understand AgNPs transport behaviour. PVP coated AgNPs remained colloidally stable, with their transport in the water column dominated by diffusion, and exhibited no significant or substantial changes in data or model parameters for different seasons. Citrate coated AgNPs were susceptible to rapid aggregation, sedimentation, dissolution and reprecipitation; their transport in the water column was determined by both diffusion and sedimentation.