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. The authors studied the apparent sedimentation rates of selected ENPs (cerium dioxide [CeO2 ], polyvinylpyrrolidone-capped silver [PVP-Ag], and silica-coated silver [SiO2 -Ag]) in agitated sediment-water systems resembling fresh, estuarine, and marine waters.

Estimation of in situ sediment-to-water fluxes of polycyclic aromatic hydrocarbons, polychlorobiphenyls and polybrominated diphenylethers.

Sediment-water fluxes of hydrophobic organic chemicals (HOC) may affect the quality of surface waters. Here, we present an approach to derive such fluxes from (a) in situ HOC concentration gradients measured with passive samplers and (b) mass transfer coefficients measured with a novel flux method using Empore disks. For eight undisturbed sediments, this method identified whether the sediment acted as a source or as a sink for HOCs.

Aquatic ecotoxicity tests of some nanomaterials.

Nanoparticles of TiO2, ZrO2, AL2O3, CeO2, fullerene (C60), single-walled carbon nanotubes, and polymethylmethacrylate were tested for ecotoxic effects using one or more ecotoxicity endpoints: Microtox (bacteria), pulse-amplitude modulation (algae), Chydotox (crustaceans), and Biolog (soil enzymes). No appreciable effects were observed at nominal concentrations of up to 100 mg/L. Dilution of nanoparticle suspensions, either in ultrapure (Milli-Q) water or in natural (pond) water, led to formation of larger particles, which settled easily.