Antioxidant collapse and microbial metabolic shift underlie perfluorooctanoic acid toxicity in constructed wetlands

With the increasing accumulation of emerging pollutants in environment, their associated ecological risks have drawn growing attention. Perfluorooctanoic acid (PFOA), a typical persistent pollutant, is widely distributed in wastewater treatment processes and lacks effective removal methods, posing potential threats to the ecological functions of constructed wetland (CW) systems. This study constructed four vertical subsurface flow CWs, which were continuously operated for 100 days under low (0.1 mg/L), medium (1 mg/L), and high (10 mg/L) PFOA concentrations to systematically investigate their ecological effects on wetland performance. Results demonstrated that low-concentration PFOA caused no significant inhibition on total phosphorus, and nitrogen removal efficiency of CWs, while medium and high-concentration of PFOA significantly inhibited all contaminations efficiency. Plant physiological responses revealed that although Iris pseudacorus L. have the ability to absorb PFOA, PFOA can reduce their photosynthetic capacity, and damage to the plant cell membrane. Meanwhile PFOA induced an imbalance in plant antioxidant enzyme activities, specifically characterized by increased activities of superoxide dismutase and catalase coupled with decreased peroxidase activity. This was further evidenced by elevated malondialdehyde content, which ultimately resulted in oxidative damage to the plants. Besides, the content of tryptophan secreted by microorganisms increased significantly with PFOA. The specialist taxa in the community structure changed more obvious than the generalist taxa. Nitrogen metabolism tends to transform into sulfur-coupled nitrogen transformation. This study elucidates the multidimensional impacts of PFOA on CW functionality and provides a theoretical foundation for ecological risk management and restoration strategies in PFOA-containing wastewater treatment systems.