Photoinduced toxicity of retene to Daphnia magna under enhanced UV-B radiation

The effects of UV radiation on the acute toxicity of retene (7-isopropyl-1- methylphenanthrene) to Daphnia magna Straus were studied, Dehydroabietic ac id (DHAA) from which retene is formed in the vicinity of pulp and paper ind ustry was also studied. Pyrene, anthracene, and phenanthrene were used as m odel PAH compounds. The time taken for immobilization (ET50) was monitored under biologically effective UV-B dose rates of 240, 365, 565, and 650 mW m (-2) (UV-A and visible light also present). Median effective concentrations (EC50) were determined after a 15-min UV exposure (565 mW m(-2)) followed by 24 h in the dark. Retene (10-320 mug l(-1)) was not acutely toxic in the dark. The induction of phototoxicity was in agreement with the absorption properties of the compounds (absorption peak of retene at around 300 nm). P hotoinduced toxicity followed an order pyrene > anthracene > retene. Phenan threne and DHAA were not acutely phototoxic. Accumulation of the compound i n Daphnia before UV exposure was essential. Some changes in the absorption spectra of the compounds were seen after a 5-h UV irradiation (565 mW m(-2) ), but none of the irradiated compounds were acutely toxic without further UV exposure. Therefore, the enhanced acute toxicity was primarily due to in ternal photosensitization reactions rather than photomodification. The diss olved fraction of 25% pulp and paper mill effluent reduced phototoxicity by attenuating UV radiation. The phototoxicity of retene was a function of bo th the exposure concentration and the UV-B dose rate, but relatively high U V-B dose rates and concentrations were needed for the acute photoinduced to xicity. (C) 2001 Elsevier Science Ltd. All rights reserved.