T. japonicus was exposed to 10 nitro-PAHs and low-intensity light irradiation. The toxicity of 9 nitro-PAHs was induced by the light irradiation. The toxicity of 1-nitropyrene was induced >1000 times higher than that in darkness. The toxicity of 1-nitropyrene increased with generation of ROS. Ascorbic acid suppressed generation of ROS and the toxicity of 1-nitropyrene.