Transport and retention of differently coated CeO2 nanoparticles in saturated sediment columns under laboratory and near-natural conditions

Abstract

Where surface-functionalized engineered nanoparticles (NP) occur in drinking water catchments, understanding their transport within and between environmental compartments such as surface water and groundwater is crucial for risk assessment of drinking water resources. The transport of NP is mainly controlled by (i) their surface properties, (ii) water chemistry, and (iii) surface properties of the stationary phase. Therefore, functionalization of NP surfaces by organic coatings may change their fate in the environment. In laboratory columns, we compared the mobility of CeO 2 NP coated by the synthetic polymer polyacrylic acid (PAA) with CeO 2 NP coated by natural organic matter (NOM) and humic acid (HA), respectively. The effect of ionic strength on transport in sand columns was investigated using deionized (DI) water and natural surface water with 2.2 mM Ca 2+ (soft) and 4.5 mM Ca 2+ (hard), respectively. Furthermore, the relevance of these findings was validated in a near-natural bank filtration experiment using HA-CeO 2 NP. PAA-CeO 2 NP were mobile under all tested water conditions, showing a breakthrough of 60% irrespective of the Ca 2+ concentration. In contrast, NOM-CeO 2 NP showed a lower mobility with a breakthrough of 27% in DI and < 10% in soft surface water. In hard surface water, NOM-CeO 2 NP were completely retained in the first 2 cm of the column. The transport of HA-CeO 2 NP in laboratory columns in soft surface water was lower compared to NOM-CeO 2 NP with a strong accumulation of CeO 2 NP in the first few centimeters of the column. Natural coatings were generally less stabilizing and more susceptible to increasing Ca 2+ concentrations than the synthetic coating. The outdoor column experiment confirmed the low mobility of HA-CeO 2 NP under more complex environmental conditions. From our experiments, we conclude that the synthetic polymer is more efficient in facilitating NP transport than natural coatings and hence, CeO 2 NP mobility may vary significantly depending on the surface coating. Electronic supplementary material The online version of this article (10.1007/s11356-019-04965-x) contains supplementary material, which is available to authorized users.

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