UV-B radiation induces DEHP degradation and their combined toxicological effects on Scenedesmus acuminatus

The co-contamination discharge of Phthalate esters (PAEs) by human activities and the increased UV radiation is increasing in aquatic ecosystems. However, little information is available about the combined detrimental effects of UV and PAEs on phytoplankton. In this study, the combined effects of UV-B irradiation and di-(2-ethylhexyl) phthalate (DEHP) on photosynthesis and antioxidant system of Scenedesmus acuminatus, and the DEHP degradation were investigated. Results showed that UV-B radiation decreased the chlorophyll a fluorescence yield, photosynthetic activity (Fv/Fm), pigment content and superoxide dismutase activity. This radiation also increased the reactive oxygen species (ROS) production and soluble protein and malondialdehyde contents. UV-B radiation with 10 mg L-1 DEHP improved the Fv/Fm and alleviated the cell damage of S. acuminatus, and the addition of high DEHP concentration (>= 50 mg L-1) aggravated cell damage. The ROS generation also decreased with the increased DEHP concentration. UV-B radiation can effectively promote the DEHP degradation, with the highest degradation rate of 89.9% at an initial DEHP concentration of 10 mg L-1 within 6 h. This result may be attributed to that UV-B irradiance induced DEHP degradation under the regulation of ROS generated by S. acuminatus. Our findings will contribute to the understanding of the combined toxic mechanisms of UV-B and DEHP and in the evaluation of ecological environment risks for primary producers in aquatic ecosystems.