UV Light Combined with Nitrate Remove Bisphenol A: Kinetics, Transformation Pathways, and Acute Toxicity Assessment

Abstract

As a powerful endocrine disruptor, bisphenol A (BPA) is a serious threat to human health. In this study, low-pressure UV lamp (LP-UV) photolysis nitrate was used to degrade BPA in different aqueous solutions. Results showed that BPA could be decomposed efficiently in the UV/nitrate process. ·OH played a significant role in the UV/nitrate process, and the steady-state concentration of ·OH ([·OH]ss) was calculated to be 5.26×10-15 M under control conditions. 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 (kobs) increased with nitrate concentration since more activity species were generated in high nitrate concentration. BPA degradation rate significantly accelerated as the pH value rose, it was ascribed to the increase of the molar absorption coefficient and the portion of ionic BPA. However, kobs declined with increasing BPA concentration result from the inner filter effect and the competition of more generated intermediate products. The increasing decomposition of BPA with the addition of HCO3-/CO32- (0~10 mM), which could be explained as HCO3-/CO32- scavenged ·OH resulting in the accumulation of ·NO2. The effect of Cl- (0~20 mM) can be ignored, which suggested reactive chlorine radicals degraded BPA effectively. The kobs reduced acutely when NOM (0~5mg-C/L) existed in the solution, this could be ascribed to the dual role of NOM inner filter effect and reactive radicals 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/nitrate process.