Influence of NOM on the Stability of Zinc Oxide Nanoparticles in Ecotoxicity Tests

Abstract

Nanomaterials are known to aggregate in the presence of ions. Similarly, the aggregation of zinc oxide nanoparticles (ZnO NPs) exposed to various ions such as sodium chloride and calcium chloride in water systems increases with the ionic strength. Therefore, for accurate toxicity studies, it is necessary to conduct a test using natural organic matters (NOMs) as additional dispersants that strengthen stability with increased repulsive forces. The three types of ecotoxicity tests based on the dispersion stability test using NOM showed that the toxicities of the three test samples decreased in the presence of NOM. To determine how NOM improved dispersion and reduced toxicities, we analyzed the ionization degree of ZnO NPs with and without NOM and found that the solubility was below 2 mg/L with a negligible change over time, implying that the ionization effect was low. The absolute value of the surface charge of particles increased in the presence of NOM, resulting in increased repulsive electrostatic forces and steric hindrance, causing less aggregation and more dispersion. Additionally, although the NOM used in the test is considered an effective dispersant that does not have a toxicological effect on aquatic organisms, the presence of NOM resulted in reduced toxicities and should be further investigated to establish it as a standard test method.

Behaviour of advanced materials in environmental aquatic media – dissolution kinetics and dispersion stability of perovskite automotive catalysts

“…5A). This theory is confirmed by the experimental evidence provided by Lee et al 22 They performed dispersion stability studies on ZnO NPs following TG318 and observed that ZnO is highly stable in low IS media and low hardness media (comparable to EPA soft) without NOM addition. They monitored stability higher than 90% for more than 48 h. In contrast to a mid IS medium with increased hardness, comparable to M7, complete sedimentation was achieved already in the first 6 h; upon NOM addition, a drastic increase in the stability was observed, up to 90% of particles were in dispersion for more than 48 h. This is in line with the significant increase in dissolution observed for ZnO in M7 media, shown in Fig.…”

“…All experiments were performed on LaCoNi, given that previous studies already addressed the stability in dispersion of the reference materials selected. 22 Based on the dissolution studies, the doping of Pd or Pt was not relevant enough to account for differences in the perovskites' behaviour in dispersion. The concentration of LaCoNi stock suspension was in the range recommended by the OECD guideline to achieve comparable results among materials with different sizes, i.e., 0.5 × 10 12 to 5 × 10 12 particles L −1 .…”

ZnO Nanomaterials and Ionic Zn Partition within Wastewater Sludge Investigated by Isotopic Labeling

“…, the authors show that the presence of NOM reduces the toxicity of ZnO NPs in terms of algal‐growth inhibition, where the reported EC 50 concentrations are on the order of 100s of µg g −1 . [ 32 ] For 10 µg g −1 or less, there is a negligible difference in the growth inhibition with and without the presence of NOM. In the same study, decreased toxicity was reported in a Daphnia magna immobilization test for µg g −1 level of ZnO NPs due to the presence of NOM.…”

Influence of Humic Acid on the Transport of Two Types of Synthesized Zinc Oxide Nanoparticles in Quartz Sand

“…#2S101H, International Humic Substances Society), which is used frequently in colloid transport studies, was used as a humic substance. The SRHA stock solution was prepared according to a method reported previously [15,19]. First, 25 mg of dried SRHA was placed into 50 mL Milli-Q water (Q-Gard) and was stirred for 24 h. The solution was filtered using a 0.22 μm filter, and its pH was adjusted to 8.0 using 0.1 M NaOH.…”

“…In particular, zinc oxide nanoparticles (ZnO-NPs) are used widely in the fields of cosmetics, optics, and the chemical industry [5,6] due to their multifunctional properties, and also for nanocomposite development [7]. Adverse effects of ZnO-NPs on living organisms have been reported frequently, e.g., [8][9][10][11][12][13][14][15]. For example, the toxicity of ZnO-NPs in plants [10,11], bacteria [8,16], and rodents [17] has been reported.…”