Impact of water composition on association of Ag and CeO2 nanoparticles with aquatic macrophyte Elodea canadensis

In this study, the potential association of (citrate-stabilized) Ag (14.1 ± 1.0 nm) and CeO₂ (6.7 ± 1.2 nm) engineered nanoparticles (ENPs), or their ionic counterparts, with the submerged aquatic plant Elodea canadensis, was examined and, in particular, parameters affecting the distribution of the nanoparticles (or metal ions) between plant biomass and the water phase were assessed using five distinct aqueous matrices (i.e. tap water, 10 % Hoagland’s solution and three natural surface water samples). Individual plants were exposed to varying concentrations of Ag and CeO₂ ENPs or Ag⁺ and Ce³⁺ ions during 72-h-lasting batch experiments. A dose-dependent increase of silver or cerium in plant biomass was observed for both the nanoparticles and the ions, whereby exposure to the latter systematically resulted in significantly higher biomass concentrations. Furthermore, the apparent plant uptake of CeO₂ ENPs appeared to be higher than that for Ag ENPs when comparing similar exposure concentrations. These findings suggest that association with E. canadensis might be affected by particle characteristics such as size, composition, surface charge or surface coating. Moreover, the stability of the ENPs or ions in suspension/solution may be another important aspect affecting plant exposure and uptake. The association of the nanoparticles or ions with E. canadensis was affected by the physicochemical characteristics of the water sample. The silver biomass concentration was found to correlate significantly with the electrical conductivity (EC), dry residue (DR) and Cl⁻, K, Na and Mg content in the case of Ag ENPs or with the EC, inorganic carbon (IC) and Cl⁻, NO₃⁻, Na and Mg content in the case of Ag⁺ ions, whereas significant relationships between the cerium biomass concentration and the EC, DR, IC and Ca content or the pH, EC, DR, IC and Cl⁻, Ca and Mg content were obtained for CeO₂ ENPs or Ce³⁺ ions, respectively. Results also indicated that the Ag ENPs and Ag⁺ ions might potentially be toxic towards E. canadensis whereas no evidence of phytotoxicity was noted in the case of CeO₂ ENPs or Ce³⁺ ions.