Eye irritation testing of nanomaterials using the EpiOcular™ eye irritation test and the bovine corneal opacity and permeability assay

Background: Assessment of eye irritation hazard has long been a core requirement in any chemical legislation. Nevertheless, publications focussing on the eye damaging potential of nanomaterials are scarce. Traditionally, eye irritation testing was performed using rabbits. The OECD Test Guideline 437 Bovine Corneal Opacity and Permeability (BCOP) test method allows determining severely irritating substances without animals, and the recently adopted OECD Test Guideline 492 Reconstructed human cornea-like epithelium test method allows identifying chemicals that neither induce eye irritation nor serious eye damage. For substances applicable to these tests, huge progress has been made in replacing animal testing. Methods: The in vitro eye irritation potential of 20 nanosized and 3 non-nanosized materials was investigated in a 2-tier EpiOcular (TM) Eye Irritation Test (EpiOcular (TM)-EIT) and BCOP testing strategy including histopathology of the bovine corneas. Furthermore, applicability of the testing strategy for nanomaterials was assessed. Test materials encompassed OECD representative nanomaterials (metals (Ag), metal oxides (ZnO, TiO2, CeO2), amorphous SiO2 and MWCNTs), three organic pigments, quartz, and talc. Results: None of the dry-powder nanomaterials elicited eye irritation in either the EpiOcular (TM)-EIT or the BCOP assay. Likewise, an amorphous SiO2 nanomaterial that was supplied as suspension was tested negative in both assays. By contrast, in the EpiOcular (TM)-EIT, the silver nanomaterial that was supplied as dispersion was tested positive, whereas its surfactant-containing dispersant was borderline to negative. In the BCOP assay, the silver nanomaterial elicited highly variable results and dark-brown patches remained on the corneal surface, whereas the results for its dispersant alone were borderline to positive, which was assessed as inconclusive due to high inter-assay variability. Conclusion: The present study points to the low eye irritation potential of a spectrum of nanomaterials, which is consistent with available in vivo data for the same test materials or for nanosized or bulk materials of the same composition.