Degradation of Triclosan in soils by thermally activated persulfate under conditions representative of in situ chemical oxidation (ISCO)

As a widely used antimicrobial agent, Triclosan (TCS) may potentially enter the environment, thus invoking significant environmental concerns due to its high toxicity to organisms. The present study demonstrated that a thermally activated persulfate (PS) oxidation process could effectively degrade the TCS in various arable topsoils. Eighty percent of the TCS at 50 mg kg(-1) in Zhe Jiang (ZJ) soil could be degraded after a 360 min reaction in the presence of 18.8 mM of PS. Increased PS concentrations significantly increased the efficiency of the degradation. Elevated temperatures were favorable for TCS degradation, and the apparent activation energy E-alpha was determined to be 74.3 kJ mol(-1). The oxidation efficiency gradually decreased with the increase of the pH from 3 to 11. An electron paramagnetic resonance (EPR) experiment and radical scavenging test confirmed that both OH center dot and SO4 center dot- existed during oxidation, and SO4 center dot- was the dominant radical species. The degradation efficiency of TCS was higher than that of Triclocarban (TCC), another widely used antimicrobial agent, which might be attributed to the electro-donating phenolic (-OH) and ether (-O-) groups in the molecular structure of TCS. The degradation of TCS in three arable topsoils indicated that the soil organic matter played a dominant role in TCS degradation. In ZJ soil, after the oxidation process, the soil's SOM was decreased by 14%, and the breakdown of large soil aggregates into smaller ones was found. Moreover, two degradation products of TCS were identified, e.g., penta-hydroxylated and hexa-hydroxylated TCS, which may be less toxic. The degradation was induced by phenol ring hydroxylation, and the underlying oxidation mechanisms are given.