Low-concentration PVC microplastics alleviate the physiological toxicity of nortriptyline to Chlorella vulgaris and enhance its drug removal capacity

Antidepressant drugs and microplastics are extensively found in environmental media, and their combined pollution effects may lead to potential ecological risks in a synergistic manner. The study investigates the combined effects of microplastics and nortriptyline, with particular emphasis on how microplastics influence the toxic mechanisms of nortriptyline in Chlorella vulgaris and its removal efficiency. Key physiological parameters were monitored, including dry weight, photosynthetic pigments contents, chlorophyll fluorescence parameters (Fv/Fm, ΦPSII, ETRmax, α, Ik), antioxidant enzyme activities, malondialdehyde (MDA), and total protein contents. The results showed that PVC microplastic could reduce the toxicity of nortriptyline to C. vulgaris and enhance the alga's removal efficiency of nortriptyline from water. After 6-day exposed to 5 and 25 mg/L nortriptyline, Photosynthetic pigment contents in the co-exposure group were elevated relative to those in the microalgae exposed to nortriptyline alone, accompanied by reduced antioxidant enzyme activities and malondialdehyde levels. Low concentration of PVC microplastic enhanced the removal efficiency of 5 mg/L nortriptyline by 29.98% and that of 25 mg/L nortriptyline by 40.46%. These findings provide a scientific basis for the development of management and remediation strategies in aquatic systems co-contaminated with nortriptyline and microplastics.