Ferrate-mediated degradation of ambroxol in water: Kinetics, reaction mechanism, and simultaneous phosphorus removal

Ambroxol (AMB), a widely used medicine for bronchitis and other respiratory and lung diseases, is an emerging aquatic pollutant whose removal has been insufficiently studied. In this work, we investigated the kinetics, products, and reaction mechanism of AMB by ferrate (Fe(VI)) in aqueous solutions. Experiments showed that Fe(VI) reacts efficiently with AMB under neutral conditions (pH=7), with an apparent second-order rate constant of (5.840.22)× 10 2 M −1 s −1 , degradation efficiency increased with Fe(VI) concentration across the tested range (10–200 μM). At a [Fe(VI)]:[AMB] molar ratio of 10:1, complete removal of AMB was achieved within 300 s. The degradation process proved robust, showing minimal influence from common inorganic ions, although slight inhibition was observed in the presence of Ca 2+ and humic acid. We identified seven intermediates and proposed four reaction pathways. Notably, the feasibility of this process was further confirmed in real water matrices. In addition, Fe(VI) application enabled simultaneous removal of both phosphorus and AMB, achieving a 46% reduction in total phosphorus (initial 5 mg L − 1 ) at 2 mM Fe(VI), attributable to the coagulation by in situ-formed iron hydrolysis products. However, ecological risk assessment of the transformation products formed under the studied conditions indicated that several transformation products may present potential hazards due to their persistence and predicted toxicity. Several products pose non-negligible risks to aquatic ecosystems and public health owing to their acute/chronic toxicity, environmental persistence, and endocrine-disrupting potential. This study demonstrates that Fe(VI) is a promising technology for the co-removal of AMB and phosphorus from water, while underscoring the necessity to manage the environmental risks associated with the resulting transformation products.