Microplastic-mediated transfer of parabens and its ecotoxicological impact on Chlorella vulgaris

Microplastics (MPs) are pervasive contaminants in aquatic systems and wastewater (WW), with polystyrene microplastics (PS-MPs) posing remarkable ecotoxicological risks and acting as potential carriers for other emerging contaminants (ECs), such as parabens - widely used preservatives and frequently detected in WW. The co-occurrence of MPs and ECs raises concerns regarding their combined effects on WW treatment efficiency and ecosystem health. This study evaluated the individual and combined effects of PS-MPs and methylparaben (MetP) on the physiological responses and bioremediation capacity of the microalga Chlorella vulgaris in synthetic wastewater (SWW). Short-term exposure (72 h) to PS-MPs and MetP impaired microalgal metabolism and induced reactive oxygen species (ROS) accumulation. After 168 h, C. vulgaris recovered metabolic activity, indicating activation of adaptive defense mechanisms. PS-MPs caused moderate growth inhibition (14%), whereas MetP alone or combined with PS-MPs did not significantly affect microalgal growth. Despite these stress responses, nutrient removal remained high, with nitrogen (N) removal reaching 80% and phosphorus (P) removal between 63 and 70%. Regarding contaminant fate, C. vulgaris removed 21.34 ± 1.12% of MetP, a process significantly enhanced by PS-MPs (26.20 ± 4.44%), which is consistent with a potential carrier role. Adsorption assays confirmed that PS-MPs retained 0.61 ± 0.05 mg MetP per gram, demonstrating their capacity to sorb MetP and potentially modify its partitioning under the tested conditions, while no significant PS-MPs degradation occurred within 168 h. Overall, C. vulgaris exhibited resilience under combined contaminant exposure, maintaining WW polishing performance and partially eliminating organic micropollutants. These findings highlight the potential of microalgal systems as eco-efficient solutions for managing MPs and co-contaminants in WW treatment.