COMBINED EXPERIMENTAL AND THEORETICAL STUDY ON PHOTOINDUCED TOXICITY OF AN ANTHRAQUINONE DYE INTERMEDIATE TO DAPHNIA MAGNA

The toxicity of chemicals can be enhanced by light through two photochemical pathways: Photomodification to more toxic substances and photosensitization. In the present study, the reactive oxygen species (ROS) mechanism for photoinduced acute toxicity of 1-amino-2,4-dibromoanthraquinone (ADBAQ) to Daphnia magna was clarified by experiment and theoretical calculation. The results of the present study show that ADBAQ exhibited high toxicity to D. magna under simulated solar radiation (SSR), with a median effective concentration of 1.23 +/- 0.19 nM (mean +/- standard deviation). The photomodified ADBAQ (mixtures of ADBAQ and its photoproducts) was less phototoxic than the intact ADBAQ. The SSR-only or ADBAQ-only treatments did not affect the ROS level in D. magna, whereas increased ROS levels were observed in the presence of SSR and ADBAQ. The ROS in vivo were determined by measuring the fluorescence of 2 ', 7'-dichlorofluorescein, which is a useful technique to assess toxicity of chemicals to aquatic organisms. The antioxidants, including vitamin C, vitamin E, and beta-carotene, decreased the photoinduced oxidative damage to D. magna, probably by scavenging ROS. These experimental results demonstrate that photosensitization is the potential mechanism of photoinduced toxicity of ADBAQ to D. magna. Proposed phototoxic pathways of ADBAQ were elucidated by means of time-dependent density functional theory. The theoretical calculation indicates that superoxide anion and singlet oxygen are able to be generated through electron transfer or energy transfer in the photosensitization reactions.