Influence of microplastic exposure on nutrient uptake and growth performance of Chlorella vulgaris

Background: Microplastics (MPs) are persistent emerging contaminants frequently detected in wastewater (WW), where conventional treatment systems often fail to remove them, posing environmental and Human health risks [1]. Microalgae-based systems have emerged as sustainable alternatives for WW remediation due to their capacity for contaminants and nutrient removal [2]. However, the effects of MPs on microalgal performance and treatment efficiency under different WW operational conditions remain poorly understood. Objective: This study evaluated the physiological responses and bioremediation performance of Chlorella vulgaris exposed to different types of MPs under varying WW conditions. Methods: C. vulgaris was exposed to 100 mg/L [3] of five commonly detected MPs: polypropylene (PP), polystyrene (PS), polyamide (PA), low-density polyethylene (LDPE), and high-density polyethylene (HDPE). Experiments were conducted under different WW conditions: variations in nitrogen (N) availability, organic carbon concentration, and photoperiod regimes (12:12 h light/dark cycle versus continuous light). Microalgal growth, metabolic activity, and bioremediation efficiency were assessed. Results: MPs induced heterogeneous metabolic responses depending on the MPs’ type and environmental conditions. HDPE and LDPE consistently reduced esterase activity, whereas PS increased esterase activity under N-limited conditions. LDPE also induced intracellular oxidative stress specifically under N limitation. Despite these effects, C. vulgaris maintained growth and biomass production in most scenarios. Growth inhibition (13-27%) occurred only under combined nutrient starvation and a 12:12 h photoperiod. Heterotrophic metabolism partially compensated for reduced photosynthetic activity during dark phases. Under N-limited conditions, C. vulgaris achieved high bioremediation efficiency, removing up to 94 % of N and >97.5 % of glucose even in the presence of MPs. In contrast, limited organic carbon impaired nutrient removal due to energy constraints. Conclusions: Overall, WW conditions strongly modulated the physiological stress induced by MPs. Nutrient limitation and light/dark cycles intensified metabolic disturbances, whereas N-limited environments promoted adaptive responses that supported microalgal resilience. C. vulgaris maintained high bioremediation capacity in most conditions, highlighting its potential as a robust and eco-friendly tool for polishing MP-contaminated wastewater. Figure 1. Wastewater bioremediation performance by exposing Chlorella vulgaris to different types of MPs, at 100 mg/L, under varying wastewater operational conditions.