Effects of sedimentary organic matter degradation and structure on nonylphenol degradation by sodium persulfate

Abstract

The structure and constituents of sedimentary organic matter (SOM) in the degradation of benzene ring-14C labeled 4-nonylphenol (14C-NP) by sodium persulfate (Na2S2O8) were investigated. Na2S2O8 mineralized over 84 % of 14C-NP to 14CO2, and no parent unlabeled 4-nonylphenol (NP) compounds were detected in the water-soluble/supernatant phase or extractable residues. Organic carbon (OC) was sequentially separated from six sediment samples collected from the Pearl River (BET), estuary (GSD), continental shelf (S11 and S21), and deep sea (M9 and M10). Demineralized OC (DM), unstable OC (USOC), nonhydrolyzable OC (NHC), and resistant OC (ROC) were obtained and characterized using solid-state 13C nuclear magnetic resonance (SS-NMR). The correlations among USOC, NHC, and the degradation kinetic constant of 14C-NP (kNP) were significant (R2 > 0.86, p < 0.01), indicating that USOC and NHC were the main factors controlling 14C-NP degradation. SOM structure and constituent analyses indicated that O-alkyl C + OCH3/NCH C + COO/NC=O C and carbohydrate + protein were positively related to Ln(kNP) (R2 > 0.72, p < 0.05) because these structures were unstable. However, the stable structures (Alkyl C and Arom CC) and constituents (sporopollenin, algaenan, and char) hindered 14C-NP degradation because they were negatively related to Ln(kNP) (R2 > 0.81, p < 0.05). The OC removal rate was positively correlated with 14C-NP degradation (R2 > 0.86, p < 0.01), indicating that the NP was primarily degraded in parallel with the breakdown of SOM. Stoichiometric analysis showed that Na2S2O8 effectively oxidized over 58 % of the OC to CO2, and the electron transfer efficiency was 17.2–69.5 %. This study is the first to emphasize the importance of SOM degradation, structure, and constituents in the degradation of NP by persulfate.