Effects of tritium pollution on photosynthesis, respiration and redox of microalgae under rising temperature

Due to rising sea surface temperatures and thermal emissions from nuclear power plants, temperature has been recognized as a significant factor in evaluating the potential biological effect of tritium. In this work, tritium pollution in a freshwater system was simulated, and the dynamic changes of microalgal growth in semi-natural state were monitored in real time. The effects of tritium exposure on photosynthesis and respiration of Chlamydomonas reinhardtii (C. reinhardtii) were further analyzed in the context of rising temperatures. It was found that under tritium exposure (3.7 × 10⁶ Bq/L, 12.17 μGy/h, resulting in a dose for 96 h of exposure is about 1 mGy), elevated temperature promoted the accumulation of organically bound tritium (OBT) and reactive oxygen species (ROS), which damaged the cell structure, reduced the photosynthetic performance and photosynthetic energy transfer efficiency, and interfered with the energy levels and redox states in C. reinhardtii. At the transcriptional level, elevated temperature exacerbated the inhibition of tritium exposure on key metabolic pathways related to photosynthetic system and respiratory metabolism of C. reinhardtii, while simultaneously causing double-stranded DNA damage in algal cells. Under the low-dose of tritium exposure with elevated temperature, the accumulation of ROS may lead to the disruption of algae's defense mechanisms, subsequently reducing their ability to resist genetic damage. This study provides insights for reassessing the potential risks to aquatic ecosystem considering the discharge of low-level tritium-containing wastewater in the context of global warming.