Experimental and theoretical studies on the photoinduced acute toxicity of a series of anthraquinone derivatives towards the water flea (Daphnia magna)

The photoinduced acute toxicity of fourteen anthraquinone derivatives to Daphnia magna was investigated. Whilst in the dark, all of dyes exhibited no observable toxicity at the maximum test concentration used, in the presence of visible light, all of the colorants, with the exception of three nitroanthraquinones, were acutely toxic towards the water flea over a wide range of medium effective concentrations (4.3–4186.7 nmol L−1). Generally, the acute toxicity of the dyes was higher in the presence of full-spectrum simulated solar radiation compared with visible light; in addition, the photoinduced toxicity of the dyes increased with increase in their hydrophobicity. The energy gap between the lowest unoccupied molecular orbital and the highest occupied molecular orbital was found to indicate the relative photoinduced toxicity of the dyes. Time-dependent density functional theory calculations revealed that singlet oxygen and the superoxide anion could be generated through direct energy transfer or autoionization of the excited state of the dyes.