Degradation of triclosan by an integrated nano-bio redox process.

In this study, a sequential reduction-oxidation method was developed for complete degradation of triclosan (2,4,4'-trichloro-2'-hydroxydiphenyl ether, TCS) in aqueous solution. Rapid reductive dechlorination of TCS was achieved with palladized zero-valent iron nanoparticles (Pd/nFe), under anaerobic conditions, with generation of 2-phenoxyphenol as the sole dechlorination product. Sequentially, 2-phenoxyphenol was transformed into a non-toxic polymer using laccase (EC:1.10.3.2) derived from Trametes versicolor in the presence of natural redox mediator syringaldehyde (SYD). High performance liquid chromatography combined with electrospray ionization mass spectroscopy (HPLC-ESI-MS) revealed the formation of dimer and trimer products during the laccase-mediated transformation process. The efficiency of the integrated method is critically dependent on the Fe(2+) concentration, which was effectively controlled by optimizing the solution pH. To the best of our knowledge, this is the first report of a redox two-step hybrid system for the complete transformation of TCS into non-toxic products.

Bokare V ，Murugesan K ，Kim YM ，Jeon JR ，Kim EJ ，Chang YS ... -  《-》

Effect of Fe-Pd bimetallic nanoparticles on Sphingomonas sp. PH-07 and a nano-bio hybrid process for triclosan degradation.

In this study, we have evaluated the effect of palladium-iron bimetallic nanoparticles (nFe-Pd) on diphenyl ether (DE) degrading bacterial strain Sphingomonas sp. PH-07 as well as a sequential nano-bio hybrid process with nFe-Pd as catalytic reductant and PH-07 as biocatalyst for degradation of triclosan. Strain PH-07 grew well in the presence of nFe-Pd up to 0.1g/L in minimal salts medium with DE as carbon source. In aqueous system, TCS (17.3 μM) was completely dechlorinated within 2h by nFe-Pd (0.1g/L) with concomitant release of 2-phenoxyphenol (16.8 μM) and chloride ions (46 μM). All possible dichloro- and monochloro-2-phenoxyphenol intermediates were identified by HPLC and GC-MS analyses, and the dechlorination pathway was proposed. Addition of PH-07 cells into the reactor effectively degraded the 2-phenoxyphenol. Our results reveal that strain PH-07 survives well in the presence of nFe-Pd and nFe-Pd/PH-07 hybrid treatment could be a potential strategy for degradation of TCS.

Murugesan K ，Bokare V ，Jeon JR ，Kim EJ ，Kim JH ，Chang YS ... -  《-》

Enhanced transformation of triclosan by laccase in the presence of redox mediators.

Murugesan K ，Chang YY ，Kim YM ，Jeon JR ，Kim EJ ，Chang YS ... -  《-》

Laccase- and electrochemically mediated conversion of triclosan: Metabolite formation and influence on antibacterial activity.

Metabolite formation from radical-based oxidation of the environmental pollutant triclosan (TCS) was compared using an ascomycete (Phoma sp. UHH 5-1-03) and a basidiomycete (Trametes versicolor) laccase, laccase-redox mediator systems, and electrochemical oxidation (EC). Laccase oxidation predominantly yielded TCS di- and trimers, but notably also caused TCS ether bond cleavage. The latter was more prominent during EC-catalysed TCS oxidation, which generally resulted in a broader and more divergent product spectrum. By contrast, only quantitative but not qualitative differences in TCS metabolite formation were observed for the two laccases. Application of the presumable natural laccase redox mediator syringaldehyde (SYD) shifted the TCS-transforming reactions of laccase systems from oligomerization more towards ether bond cleavage. However, the observed rapid removal of SYD from reaction systems caused by predominant adduct formation from SYD and TCS, and concomitant conversion of SYD into 2,6-dimethoxy-1,4-benzoquinone (DMBQ) clearly demonstrates that SYD does not function as a "true" laccase redox mediator in the sense of being recycled during TCS oxidation. Laccase treatment of TCS without SYD decreased the anti-bacterial TCS activity more than treatment employing SYD in addition, indicating that SYD and/or its transformation products contribute to bacterial toxicity. DMBQ was found to be about 80% more active in a bacterial growth inhibition test than its parent compound SYD in terms of IC20 values. These observations establish DMBQ as a potential cause of toxicity effects of SYD-laccase systems. They further illustrate that a natural origin of a redox mediator does not automatically qualify its use as environmentally benign or non-hazardous.

Jahangiri E ，Seiwert B ，Reemtsma T ，Schlosser D ... -  《-》

Degradation of triclosan under aerobic, anoxic, and anaerobic conditions.

Gangadharan Puthiya Veetil P ，Vijaya Nadaraja A ，Bhasi A ，Khan S ，Bhaskaran K ... -  《-》