Transformation and toxicity evolution of amlodipine mediated by cobalt ferrite activated peroxymonosulfate: Effect of oxidant concentration

Amlodipine (AML), an antihypertensive drug, has raised great environmental concerns due to the widespread occurrence in wastewater for its extensive use. In this study, we introduced an effective approach for AML removal via an oxidation reaction with peroxymonosulfate (PMS) activated by magnetic cobalt ferrite (CoFe 2 O 4 ), and highlighted the governing role of PMS concentration in the degradation process. Nearly complete removal of 10 μM AML (92.5%) was achieved in 30 min with 25 μM PMS and 40 mg/L CoFe 2 O 4 at neutral condition (pH 7.0), while the mineralization was negligible. To enhance the mineralization of AML, PMS concentration was further increased to 10 mM with the mineralization of 70.2%. A total of eight intermediates were identified using liquid chromatography-time-of-flight-mass spectrometry analysis in combination with frontier electron densities calculations, and two major transformation pathways including hydroxylation and dehydrogenation were proposed. Temporal evolution of the intermediates was monitored, of which the differences were tracked as PMS concentration increased from 25 μM to 1.2 mM. Toxicity changes throughout the degradation process were assessed on ECOSAR program, indicating that higher PMS concentration of 1.2 mM led to further reduction of potential threats, although the toxicity of some intermediates with pyridine structure needs to be further validated. Based on the findings in this study, CoFe 2 O 4 /PMS appears to be a promising alternative to remove AML from aquatic environment when appropriate PMS concentration is selected for more pronounced performance.