Session: Current Status of Environmental Research on Water Contaminants:

Quinones (QNs) are ubiquitous and play a significant role in mediating electron transport in natural and biological systems. The redox reactivity of natural organic matter (NOM) and biochars (BCs) have been attributed to their quinone components, although there is a lack of direct evidence. In this study, we examined the reactions between triclosan (TCS) as a model organohalogen and hydrobenzoquinone (BHQ). We found that when TCS was mixed with BHQ in the molar ratio of 1:1 at pH 3, 5, and 7, no TCS degradation was observed under either oxic or anoxic conditions indicating that BHQ cannot reduce TCS within the experimental period. In the mixture of TCS, Fe(III), and BHQ, TCS was degraded substantially at pH 5 and 7 with half–life of around 57 and 18 hours under anoxic conditions. In the presence of O₂, degradation of TCS was shut down completely. At pH 3, no degradation of TCS was observed in the presence and absence of O₂. The control experiment for the Fe(II) system mixed with TCS showed that no degradation of TCS was observed in the presence of Fe(II). The observed reaction between TCS and HQ in the presence of Fe (III) at pH above the pKa of BSQ (pKa = 4.1) suggests the importance of the deprotonated BSQ^- in their reaction with TCS. Reactions between two model HQs (Mitoxantrone dihydrochloride and Epigallocatechin) and TCS at pH 5 in the presence of Fe(III) showed significant TCS degradation over the reaction period of twelve days, indicating the favorable degradation of TCS by higher molecular weight HQs. A kinetic model was built to predict the rate constants of the critical reactions.

Yu Yang

Appearances