Reactive Oxygen Species Assay (OECD 495)

The Reactive Oxygen Species (ROS) Assay for Photoreactivity is an in chemico test method that is used to evaluate photoreactivity potential of a test substance by measuring ROS generated after exposure to simulated sunlight. This high throughput screening assay incorporates two reaction mixtures to detect the generation of singlet oxygen (SO) and superoxide anion (SA). Each test substance is evaluated in the two reaction mixtures in triplicate, followed by exposure to simulated sunlight, which includes UVB, UVA, and visible light. The amount of SO and SA produced are a result of the bleaching of p-nitrosodimethylaniline (RNO) and the reduction of nitroblue tetrazolium (NBT), respectively, and determined by photometric measurements. Photoreactivity potential is determined using the SO and SA thresholds presented in OECD TG 495. This test method is considered early in the assessment of photosafety to determine if further evaluation may be needed.