Pharmaceuticals and personal care products: Sources, occurrences, toxicities, and degradation by advanced oxidation and reduction processes- a review

Pharmaceuticals and personal care products (PPCPs) are emerging contaminants and widely detected in water bodies and hence, attracted the attention of researchers across the globe. The presence of these emerging contaminants (i.e., PPCPs) in water bodies has raised considerable health and environmental issues owing to their toxic, bio-accumulative, and persistent nature. These pollutants originate from different sources, such as agricultural runoff, hospital effluents, and domestic wastewater. Conventional wastewater treatment technologies are inefficient to effectively degrade and completely mineralize these pollutants, thereby necessitating the adoption of alternative advanced technologies for their effective treatment. The advanced oxidation-reduction processes (AORPs), driven by generating highly reactive oxidizing and reducing species, are found to decompose these emerging water pollutants into less/non-toxic degradation products. This review provides a comprehensive and up-to-date overview of the sources, environmental occurrences, and toxicities of PPCPs. Furthermore, it provides an in-depth evaluation of different AORPs, elucidating the mechanism, efficiencies and key roles of oxidizing species such as hydroxyl radicals (^•OH), sulfate radicals (SO₄^•–), carbonate radicals (CO₃^•–), singlet oxygen (¹O₂), superoxide radical anions (O₂^•–), and hydroperoxyl radicals (HO₂^•), and reducing species including aqueous electrons (e_aq⁻) and atomic hydrogen (H^•). Special emphasis is placed on hybrid processes (containing both oxidizing and reducing species) (i.e., AORPs) such as UV photolysis (< 187 nm), gamma-ray irradiation, and ultrasound irradiation. Finally, the review outlines current challenges and future perspectives to promote the development of more effective, sustainable, and scalable treatment technologies for water purification and environmental protection.