Heteroaggregation and sedimentation rates for nanomaterials in natural waters

•A novel method to estimate heteroaggregation rates from sedimentation is presented.•Sedimentation of nanoparticles was studied in presence of natural colloids.•Water type and nanoparticle characteristics affect these removal rates.•Parameters obtained can be used in applied water quality models for nanoparticles.

Exposure modeling of engineered nanomaterials requires input parameters such as sedimentation rates and heteroaggregation rates. Here, we estimate these rates using quiescent settling experiments under environmentally relevant conditions. We investigated 4 different nanomaterials (C60, CeO2, SiO2-Ag and PVP-Ag) in 6 different water types ranging from a small stream to seawater. In the presence of natural colloids, sedimentation rates ranged from 0.0001 m d−1 for SiO2-Ag to 0.14 m d−1 for C60. The apparent rates of heteroaggregation between nanomaterials and natural colloids were estimated using a novel method that separates heteroaggregation from homoaggregation using a simplified Smoluchowski-based aggregation-settling equation applied to data from unfiltered and filtered waters. The heteroaggregation rates ranged between 0.007 and 0.6 L mg−1 day−1, with the highest values observed in seawater. We argue that such system specific parameters are key to the development of dedicated water quality models for ENMs.

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