Impact of parabens on microalgae bioremediation of wastewaters: A mechanistic study

The rising concerns from environmental contamination by emerging contaminants (ECs) pushes the need to develop efficient removal technologies in wastewater (WW) treatment plants. Parabens are synthetic estrogens belonging to the ECs group of endocrine disrupting chemicals. Microalgae-based bioremediation is gaining attention as a compelling solution for a cost-effective and sustainable WW treatment. However, there is a lack of scientific data regarding the capacity of microalgae for the removal of parabens at different concentrations as well as the removal mechanisms involved. This work aims to study the effects from methylparaben (MetP) exposure at 0.796 and 7.96 mg/L (10 and 100 × higher than the maximum found in a WW influent) on the ability of Chlorella vulgaris to remove MetP and nutrients from a WW. This mechanistic study was undertaken using different physiological endpoints: cellular hydrophobicity (as extracellular interaction), metabolic activity, intracellular reactive oxygen species (ROS) accumulation and photosynthetic efficiency. The presence of MetP did not alter the hydrophobicity of C. vulgaris cells, which suggests that bioadsorption did not occur. Moreover, for 0.796 mg MetP/L no effects were observed in the metabolism or biomass production. However, for 7.96 mg/L, a decrease in the esterase activity and photosynthetic pigments production was observed, linking these metabolic effects with a decrease in cellular growth. After 168 h, MetP was partly removed: 33.16% and 14.10%, for initial concentrations of 0.796 and 7.96 mg/L, respectively. For the lower concentration, removal was achieved through biodegradation and photodegradation, however, for the extreme concentration, C. vulgaris was not capable to biodegrade MetP, being photodegradation the main removal mechanism. Furthermore, C. vulgaris showed satisfactory growth and removal of the main nutrients (≥73%), which were not affected by the presence of MetP at the lower concentration, highlighting the ability of this microalga for the treatment of WW contaminated with parabens, even with extreme concentrations.