L-15ex medium is a minimal medium based on Leibovitz L-15 basal cell culture medium. This medium, which was developed by Schirmer, et al. for studying the photocytotoxicity of polycyclic aromatic hydrodcarbons (PAHs) to the rainbow trout gill cell line, RTgill-W1 contains only salts, pyruvate and galactose. The simplicity of the medium favors expression of cellular responses to toxicants because protective molecules such as anti-oxidants are absent.