Effects of the structures and micropores of sedimentary organic matter on the oxidative degradation of benzo(a)pyrene by Na2S2O8

Abstract

In this study, we investigated how the desorption and degradation processes of radiolabeled benzo[a]pyrene (BaP) that was aged in various marine sediments were influenced by sedimentary organic matter properties. The stable OC fraction (STOC) and the demineralized fraction (DM) were isolated and characterized via advanced solid-state 13C nuclear magnetic resonance spectroscopy (NMR) and a CO2 gas adsorption technique, respectively. Sodium persulfate preferentially removed the unstable OC fractions (USOC) and the aromatic C groups, and the residual STOC fractions were enriched with aliphatic C groups. The aliphatic C showed stronger resistance to degradation by persulfate than that of the aromatic C. A first-order kinetic model described the degradation process by sodium persulfate solutions very well (R2 > 0.997). The desorption percentages, degradation percentages and rates k (h−1) of BaP gradually decreased from the estuarine sediments to the offshore marine sediments and were highly significantly and negatively correlated with STOC-bulk, Faliph-bulk, and Vo-bulk (R2>0.903, p < 0.01). It was demonstrated that sodium persulfate degraded not only desorbed BaP but also a portion of the bound BaP fraction that was difficult to desorb. The BaP fractions that sorbed on USOC were degraded initially; then, the fractions of BaP that were released from STOC were degraded. This study demonstrated the important roles of STOC, aliphatic moieties, and micropores in the degradation process of BaP during the Na2S2O8 treatment of the sediments.