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Systematic assessment of the water-matrix effect on the photo-Fenton oxidation of polystyrene micro-nanoplastics
Summary
Scientists tested a water treatment method that uses light, iron, and hydrogen peroxide (called photo-Fenton oxidation) to break down microscopic plastic particles in water, and found it can fully destroy these plastics even in real-world water sources like tap water, bottled water, and treated wastewater—though minerals and organic matter naturally found in water slow the process down. This matters because it shows a practical path toward removing tiny plastic particles from our drinking water and water recycling systems, which could reduce human exposure to microplastics linked to health concerns.
This study systematically evaluates the impact of water-matrix complexity on the photo-Fenton oxidation of polystyrene (PS) nanoplastics (NPs), using operating conditions previously optimized for ultrapure water ([PS NPs] 0 = 20 mg L −1 , [Fe 3+ ] = 1 mg L −1 , pH 0 = 3, and [H 2 O 2 ] 0 = 130 mg L −1 with sequential dosing). Degradation kinetics followed the Prout-Tompkins model, revealing an anionic inhibition trend (H 2 PO 4 − ≫ NO 3 − ≈ SO 4 2− > Cl − ). Phosphate was the main bottleneck due to iron complexation, whereas counter-cations showed negligible effects. The full inorganic matrix reduced the reaction rate by 45% through catalyst complexation and radical scavenging. Dissolved organic matter (DOM) further decreased the kinetic rate constant by 38–44%. Ultimately, the full complex matrix (ions + DOM) induced a 68% reduction in the reaction rate. Despite these constraints, complete mineralization of PS NPs was achieved within 40–140 min. Proof-of-concept applications in real matrices (bottled, tap, reclaimed water, and wastewater effluent) confirmed organic load as the primary kinetic driver, reducing the rate constant by up to 49%. Additionally, expanded polystyrene microplastics (MPs) removal in different real matrices exhibited significant weight loss (50–74%) with negligible final total organic carbon, indicating effective mineralization despite lower specific surface areas. SEM and TEM analyses confirmed a surface-driven degradation pathway for both NPs and MPs, progressing from the particle surface toward the core. Overall, these findings demonstrate the viability of the photo-Fenton process for removing persistent plastic contaminants in water reuse schemes.