The determination and prediction of the apparent reaction rates between excited triplet-state DOM and selected PPCPs

Abstract

To determine and predict the reaction rate between 3DOM* and PPCPs in various water bodies, this study defines a reaction rate coefficient (α3DOM∗) to describe the reaction between 3DOM* and PPCPs. As the values also included the inhibition effect of DOM's antioxidant moieties, the calculation of α3DOM∗ is inconsistent with that of a bimolecular rate constant via the steady-state kinetic method. The α3DOM∗ values of 12 selected PPCPs were determined in two DOM solutions and ten DOM-containing water samples collected from typical surface water bodies in Beijing. The Pearson coefficients between nine predictors including the absorbance ratio (E2/E3), specific absorption coefficient at 254 nm (SUVA254), fluorescence index (FI), biological index (BIX), humification index (HIX), pH, total organic carbon (TOC), total fluorescence intensity (TFI) and TOC normalized TFI (TFI/TOC) and α3DOM∗ were examined. Correlation patterns for sulfonamides, β-blockers and diclofenac supported the electron transfer pathway, and was distinctly different from those appeared for FQs where quenching effect played a main part. TFI and TFI/TOC were recognized as the most useful surrogates in empirically predicting α3DOM∗. For PPCPs that went through the electron transfer pathway, α3DOM∗ could be well fit to the Rehm-Weller model assuming a proportional relationship between TFI and △Get. For FQs, α3DOM∗ was found to linearly correlated with TFI/TOC. The α3DOM∗ values determined in this study enrich the database of PPCPs photolysis parameters, and the correlation analysis provides reference for forecasting PPCPs fate in the aquatic environment.