A Method to Assess the Relevance of Nanomaterial Dissolution during Reactivity Testing

Abstract

The reactivity of particle surfaces can be used as a criterion to group nanoforms (NFs) based on similar potential hazard. Since NFs may partially or completely dissolve over the duration of the assays, with the ions themselves inducing a response, reactivity assays commonly measure the additive reactivity of the particles and ions combined. Here, we determine the concentration of ions released over the course of particle testing, and determine the relative contributions of the released ions to the total reactivity measured. We differentiate three classes of reactivity, defined as being (A) dominated by particles, (B) additive of particles and ions, or (C) dominated by ions. We provide examples for each class by analyzing the NF reactivity of Fe2O3, ZnO, CuO, Ag using the ferric reduction ability of serum (FRAS) assay. Furthermore, another two reactivity tests were performed: Dichlorodihydrofluorescin diacetate (DCFH2-DA) assay and electron paramagnetic resonance (EPR) spectroscopy. We compare assays and demonstrate that the dose-response may be almost entirely assigned to ions in one assay (CuO in DCFH2-DA), but to particles in others (CuO in EPR and FRAS). When considering this data, we conclude that one cannot specify the contribution of ions to NF toxicity for a certain NF, but only for a certain NF in a specific assay, medium and dose. The extent of dissolution depends on the buffer used, particle concentration applied, and duration of exposure. This culminates in the DCFH2-DA, EPR, FRAS assays being performed under different ion-to-particle ratios, and differing in their sensitivity towards reactions induced by either ions or particles. If applied for grouping, read-across, or other concepts based on the similarity of partially soluble NFs, results on reactivity should only be compared if measured by the same assay, incubation time, and dose range.

Comparison of Metal-Based Nanoparticles and Nanowires: Solubility, Reactivity, Bioavailability and Cellular Toxicity

“…While all Cu-based materials (NP/NW and CuO NP) exerted very high reactivity at low concentrations around and above 0.1 g/L, about 100-fold higher concentrations were required in case of TiO 2 NP/NW, Ni NP/NW, and CeO 2 NP to exert some but still low reactivity. With regard to the respective NP, the results confirm those obtained previously [ 20 , 39 ]. No such studies have been conducted for the NW analyzed within this study.…”

“…Second, the materials themselves are able to catalyze the formation of ROS, due to their specific surface reactivity. Recent studies already demonstrated a high oxidative reactivity of different metal-based nanoparticles [ 20 ].…”

Toxicity screening and ranking of diverse engineered nanomaterials using established hierarchical testing approaches with a complementary in vivo zebrafish model

“…These results are in good agreement with earlier work, which documented that CuO, ZnO and TiO 2 -A cause higher oxidative damage relative to other ENMs. 2,3,16,40,41 Furthermore, consistent with Pal et al's findings, crystalline SiO 2 did not induce BOD in human serum, which may be a reflection of an aged crystal surface. Similarly, the rutile form of TiO 2 has been observed to have lower BOD as compared to the anatase form, which is consistent with our earlier findings.…”

An Integrated Approach to Testing and Assessment to Support Grouping and Read-Across of Nanomaterials After Inhalation Exposure

“…38 For NFs that are considered either gradually or quickly dissolving based on their dissolution rate, the relative contribution of the ion and particle components to the toxicity observed during hazard testing will need to be determined. 78 Also, the potential for the particle and ion to interact to enhance toxicity should be considered. 75…”