Differential impact of toxic twins, anthracene and phenanthrene, on photosynthetic performance, oxidative stress, and bioremediation potential of microalgae.

This study compares the physiological and biochemical effects of 3-ring polycyclic aromatic hydrocarbons (PAHs), Anthracene (ANT, linear arrangement) and Phenanthrene (PHE, angular arrangement), on microalgae Chlorella vulgaris and Scenedesmus acutus. The findings revealed that PHE exerted significant toxic effects on algal growth and photosynthetic parameters, including electron transport rate of PSII [ETR(II)] and quantum yield of PSII [Y(II)], in both species. Additionally, it significantly influenced the regulation of the non-photochemical quenching mechanism [Y(NPQ) and Y(NO)], which was responsible for the energy distribution. Moreover, it altered the photosynthetic pigments content, biomolecules profile, and non-enzymatic antioxidants in both microalgae. On the other hand, ANT exposure showed noticeable positive changes in the measured parameters. Both microalgae exhibited a slight increase in chlorophyll content, biochemical compounds, and PSII activity, with the more pronounced effects observed in S. acutus, indicating its higher resistance to ANT. Furthermore, our findings also reveal that both species effectively removed ANT and PHE from the medium within 7 days of cultivation. These findings suggest that PAH toxicity is not only influenced by molecular weight and the number of benzene rings but also by the structural arrangement of their rings. Importantly, this study highlights that both microalgae can tolerate ANT and are suitable candidates for ANT bioremediation, but not for PHE.