John Wiley & Sons, Ltd.

Rapid settling of nanoparticles due to heteroaggregation with suspended sediment

Sedimentation of engineered nanoparticles (ENPs) has been studied mainly in artificial media and stagnant systems mimicking natural waters. This neglects the role of turbulence and heteroaggregation with sediment. We studied the apparent sedimentation rates of selected ENPs (CeO2, PVP‐Ag and SiO2‐Ag) in agitated sediment‐water systems resembling fresh, estuarine and marine waters. Experiments were designed to mimic low energy and periodically resuspended sediment water systems (14 days), followed by a long term aging, resuspension and settling phase (6 months), as would occur in receiving shallow lakes. ENPs in systems with periodical resuspension of sediment were removed with sedimentation rates between 0.14 and 0.50 m/d. The sedimentation rates did not vary much among ENP type, salinity and aging time, which is attributed to the capture of ENPs in sediment flocks. The sedimentation rates were one to two orders of magnitude higher than those reported for aggregation‐sedimentation in stagnant systems without suspended sediment. Heteroaggregation rates were estimated and ranged between 0.151 and 0.547 L/mg/d, which is up to 29 times higher than those reported for natural colloids under quiescent settling conditions. We conclude that rapid scavenging and sedimentation drives removal of ENPs from the water column. Environ Toxicol Chem © 2014 SETAC

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