UV light irradiation combined with nitrate for degradation of bisphenol A: kinetics, transformation pathways, and acute toxicity assessment

Abstract

As an endocrine disruptor, bisphenol A (BPA) is a severe threat to human health. In this study, nitrate (NO₃⁻) photolysis with a low-pressure UV lamp (LP-UV) was employed to degrade BPA in different aqueous solutions. Results showed that BPA could be decomposed efficiently in the UV/NO₃⁻ process. Moreover, the contributions of UV irradiation (4.1%), ˙OH (52.7%), and reactive nitrogen species (43.2%) were obtained. The observed rate constant of BPA degradation (k_obs) increased with NO₃⁻ concentration since more active species were generated in high NO₃⁻ concentration. The BPA degradation rate was significantly accelerated as the pH value rose. This was ascribed to the increase of the molar absorption coefficient and the amount of ionic BPA under alkaline conditions. k_obs declining with increasing BPA concentration resulted from the inner filter effect and the competition of more generated intermediate products. The increasing k_obs with the addition of HCO₃⁻/CO₃²⁻ (0–10 mM) was explained as the accumulation of ˙NO₂ in the presence of HCO₃⁻/CO₃²⁻ in UV/NO₃⁻ process. The effect of Cl⁻ (0–20 mM) could be ignored in this study, which suggested that reactive chlorine radicals degraded BPA effectively. The k_obs reduced acutely when NOM (0–5 mgC L⁻¹) existed in the solution, and this could be ascribed to the dual roles of the NOM inner filter effect and reactive radical scavenging effect. Further, several degradation products were detected, and possible transformation pathways were put forward. Remarkably, the acute toxicity of BPA was slightly enhanced then decayed in the UV/NO₃⁻ process.