Exploring the degradation mechanism of bisphenol-A with low Fe2+&H2O2 content and the toxicity evolution of oxidation intermediates

Efficient and cost-effective removal of emerging contaminants from water bodies has become a global priority. This study assessed the degradation efficiency of bisphenol-A (BPA) at varying Fe²⁺&H₂O₂ (molar ratio 1:1) concentrations. In addition, the degradation mechanism of BPA by Fe²⁺&H₂O₂ and the evolution of toxicity in intermediates were examined. The results indicated that, no additional acid is needed, with a Fe²⁺&H₂O₂ concentration at 0.15 mM and a reaction time of 20 min, and the degradation efficiency of BPA exceeded 90%; this is primarily because the oxidation still occurred when Fe²⁺&H₂O₂ was added to neutral BPA solutions, possibly leading to the conversion of the active functional groups of BPA into carboxyl groups. The deprotonation of these carboxyl groups provided the acidic conditions necessary for Fenton oxidation, thereby possibly facilitating further degradation of BPA and the formation of more carboxyl-rich intermediates, replenishing acidity for Fenton reactions and promoting continuous oxidation. Moreover, highly toxic intermediates are likely to form during the degradation of BPA at a 0.05–0.1 mM Fe²⁺&H₂O₂ concentrations, but this tendency decreases substantially with increasing Fe²⁺&H₂O₂ concentrations. At a Fe²⁺&H₂O₂ concentration of 0.2 mM, the intermediates were predominantly low-toxicity or even nontoxic. These findings highlight the importance of monitoring toxicity evolution and the conditions favorable for the formation of low-toxic or nontoxic intermediates in the removal of emerging contaminants. To further validate the applicability of this method, p-chloroxylenol (PCMX) and paracetamol (PAM) were also tested under identical conditions, and both showed high degradation efficiencies under neutral pH.