An In Vitro Dosimetry Tool for the Numerical Transport Modeling of Engineered Nanomaterials Powered by the Enalos RiskGONE Cloud Platform

Dispersion and Dosimetric Challenges of Hydrophobic Carbon-Based Nanoparticles in In Vitro Cellular Studies

Methodologies across the dispersion preparation, characterization, and cellular dosimetry of hydrophilic nanoparticles (NPs) have been developed and used extensively in the field of nanotoxicology. However, hydrophobic NPs pose a challenge for dispersion in aqueous culture media using conventional methods that include sonication followed by mixing in the culture medium of interest and cellular dosimetry. In this study, a robust methodology for the preparation of stable dispersions of hydrophobic NPs for cellular studies is developed by introducing continuous energy over time via stirring in the culture medium followed by dispersion characterization and cellular dosimetry. The stirring energy and the presence of proteins in the culture medium result in the formation of a protein corona around the NPs, stabilizing their dispersion, which can be used for in vitro cellular studies. The identification of the optimal stirring time is crucial for achieving dispersion and stability. This is assessed through a comprehensive stability testing protocol employing dynamic light scattering to evaluate the particle size distribution stability and polydispersity. Additionally, the effective density of the NPs is obtained for the stable NP dispersions using the volumetric centrifugation method, while cellular dosimetry calculations are done using available cellular computational modeling, mirroring approaches used for hydrophilic NPs. The robustness of the proposed dispersion approach is showcased using a highly hydrophobic NP model (black carbon NPs) and two culture media, RPMI medium and SABM, that are widely used in cellular studies. The proposed approach for the dispersion of hydrophobic NPs results in stable dispersions in both culture media used here. The NP effective density of 1.03-1.07 g/cm3 measured here for black carbon NPs is close to the culture media density, resulting in slow deposition on the cells over time. So, the present methodology for dispersion and dosimetry of hydrophobic NPs is essential for the design of dose-response studies and overcoming the challenges imposed by slow particle deposition.

Fish acute toxicity of nine nanomaterials: Need of pre-tests to ensure comparability and reuse of data

Fish acute toxicity tests are commonly used in aquatic environmental risk assessments, being required in different international substances regulations. A general trend in the toxicity testing of nanomaterials (NMs) has been to use standardized aquatic toxicity tests. However, as these tests were primarily developed for soluble chemical, issues regarding particle dissolution, agglomeration or sedimentation during the time of exposure are not considered when reporting the toxicity of NMs. The aim of this study was to characterize the NM behaviour throughout the fish acute test and to provide criteria to assay the toxicity of nine NMs based on TiO2, ZnO, SiO2, BaSO4, bentonite, and carbon nanotubes, on rainbow trout following OECD Test Guideline (TG) nº203. Our results showed the importance of conducting a preliminary test (without fish) when working with NMs. They provide valuable information on, sample monitoring, agglomeration, sedimentation, dissolution, actual concentrations of NMs, needed to design the test. Among the NMs tested, only bentonite nanoparticles were stable during the 96-h pre-test and test in aquarium water. In contrast, the remaining NMs exhibited considerable loss and sedimentation within the first 24 h. The high sedimentation observed for almost all NMs highlights the need of consistently measuring the concentrations throughout the entire duration of the fish acute toxicity test to make reliable concentration-response relationships. Notable differences emerged in LC50 values when using actual concentrations as nominal concentrations overestimated concentrations by up to 85.6%. Among all NMs tested, only ZnO NMs were toxic to rainbow trout. A flow chart was specifically developed for OECD TG 203, aiding users in making informed decisions regarding the selection of test systems and necessary modifications to ensure accurate, reliable, and reusable toxicity data. Our findings might contribute to the harmonization of TG 203 improving result reproducibility and interpretability and supporting the development of read-across and QSAR models.