Effect of natural organic matter on cerium dioxide nanoparticles settling in model fresh water

The ecological risk assessment of chemicals including nanoparticles is based on the determination of adverse effects on organisms and on the environmental concentrations to which biota are exposed. The aim of this work was to better understand the behavior of nanoparticles in the environment, with the ultimate goal of predicting future exposure concentrations in water. We measured the concentrations and particle size distributions of CeO2 nanoparticles in algae growth medium and deionized water in the presence of various concentrations and two types of natural organic matter (NOM). The presence of natural organic matter stabilizes the CeO2 nanoparticles in suspension. In presence of NOM, up to 88% of the initially added CeO2 nanoparticles remained suspended in deionized water and 41% in algae growth medium after 12 d of settling. The adsorbed organic matter decreases the zeta potential from about −15 mV to −55 mV. This reduces aggregation by increased electrostatic repulsion. The particle diameter, pH, electric conductivity and NOM content shows significant correlation with the fraction of CeO2 nanoparticles remaining in suspension.