A comparative study of the physical and chemical properties of nano-sized ZnO particles from multiple batches of three commercial products

Given the broad commercial applications for ZnO nanomaterials, accurate attribution of physicochemical characteristics that induce toxic effects is particularly important. We report on the physicochemical properties of three commercial nano-ZnO products: Z-COTE and Z-COTE HP1 from BASF, and Nanosun from Micronisers, and, for reference, “bulk” ZnO from Sigma-Aldrich. Z-COTE, Nanosun and “bulk” consist of uncoated particles with different sizes, while Z-COTE HP1 consists of nanoparticles with a hydrophobic coating. Specific batches of these ZnO products were included in the OECD Sponsorship Programme to test manufactured nanomaterials. In order to identify properties potentially susceptible to variations between production runs, three additional batches of Z-COTE and Nanosun and two additional batches of Z-COTE HP1 were also investigated here. In general, all products showed little variation between batches for properties measured from powdered samples, but batch variations in the amount of surface coating were evident for the coated Z-COTE HP1. Properties measured with samples dispersed in liquids (agglomeration, photocatalytic activity, dissolution) were highly dependent on dispersion protocols, and this made it difficult to differentiate between differences due to dispersion and due to batches. However, batch-sensitive properties did appear to be present in Z-COTE and Z-COTE HP1 (photocatalytic activity), and Nanosun (dissolution). Intra-batch time and/or storage-dependent changes in the applied surface coating, noted specifically for the OECD batch of Z-COTE HP1, highlight the need for best practice when storing and accessing stocks of nano products. Awareness of inter-batch and intra-batch variability is essential for commercial applications and for nanotoxicological studies aimed at identifying links between physicochemical properties and any adverse effects in biological systems.