Background The Bovine Corneal Opacity and Permeability (BCOP) assay is an ex vivo test used to evaluate ocular irritation. According to the OECD Test Guideline (TG) 437, the BCOP assay can be used to identify chemicals which induce severe/corrosive eye irritation and those that do not require classification. However, BCOP has historically under-predicted certain anionic surfactants, when tested according to the standard liquid protocol. TG 437 specifies that liquid and solid surfactants may be tested as 10% aqueous dilutions for 10 minutes (although alternate dilutions and exposure times may be conducted with scientific rationale). The relevant guidance document (GD) No. 160 suggests that solid and concentrated liquid surfactants may be diluted to 10% for testing. However, GD No. 160 further directs that surfactant-based formulations are usually tested neat, but could be diluted with justification, imparting some confusion in identifying the most appropriate test methods. Additionally, as part of the EPA classification of ocular irritation, the BCOP assay may be used to assess anti-microbial products with cleaning claims. Such products may contain surfactants and are generally tested neat for classification purposes.
Methods Since neither the basis for selecting the appropriate surfactant test methods, nor the justification for modifications are clearly presented in TG 437 or GD No. 160, we present on the testing of a few common surfactant ingredients, including sodium lauryl sulfate (SLS), Triton X-100, and benzalkonium chloride, and surfactant based formulations in the BCOP assay using standard and modified dilutions and exposures to elucidate the impact of these variables on eye irritation prediction.
Results and Discussion As examples, in vitro scores of 20.7, 28.4, and 28.3 were obtained when testing SLS at concentrations of 50, 20, and 10% for 10 minutes, showing that irritation responses were not fully concentration-dependent. As a complement to the BCOP assay, histopathology was performed to assess the surfactant-induced corneal changes. Based upon these results, a framework for testing surfactant ingredients and surfactant-based formulations is proposed.