BACKGROUND: Triclosan is a biocide used in personal care products, and its presence in water bodies has been reported. This compound is suspected to be linked with the emergence of antibiotic‐resistant bacteria. In the present work, the enzyme horseradish peroxidase (HRP) was used to catalyze triclosan removal. RESULTS: The stoichiometric ratio of H2O2 to triclosan (0.83) was higher than the value predicted by the HRP catalytic cycle (0.5). During the reactions, HRP activity was gradually reduced, likely due to excess H2O2. The addition of veratryl alcohol, syringaldazine and p‐coumaric acid (redox mediators) to the reaction medium, at a mediator/triclosan molar ratio of 1.0, increased triclosan removal from 45% (without a mediator) to 56%, 64% and 80%, respectively. The antibacterial activity of these mediators was much lower than that observed for triclosan. CONCLUSION: The antibacterial activity of triclosan solution was effectively reduced after enzymatic treatment. Moreover, the enzymatic process was proven to be technically feasible for removing triclosan at an environmental relevant concentration. © 2012 Society of Chemical Industry

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Carriers with different functional groups (epoxy, aldehyde, ethyldiazonium, phenyldiazonium and amino) were tested for immobilization of T. versicolor laccase on GMA-co-EGDMA (glycidyl methacrylate-co-ethyleneglycol dimethacrylate) microspheres. Laccase immobilized on GMA-co-EGDMA containing the phenyldiazonium functional group showed the highest activity (96.3 U g -1 ). The immobilized laccase was used for removal of bisphenol-A (BPA) from aqueous solution. The temperature effect was significant on activity, but insignificant on BPA removal by the immobilized laccase. In the temperature range 10-60 °C, the removal of BPA by laccase in the immobilized form was about four times higher than that in the free form. Swelling does not affect the activity of immobilized laccase, but after 8 cycles of 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS) oxidation, non-swollen immobilized laccase was able to retain 71% of the starting activity while the 24 h swollen kept 61%. At neutral pH, adsorption onto the immobilized laccase accounted for 92% of the BPA removed while enzymatic conversion accounted for 8%. However, when increasing the pH to 10, the fraction of BPA removed by adsorption decreased to 67% and by enzymatic conversion increased to 33%.

Triclosan is a broad-spectrum biocide used in personal-care products that is suspected to be linked to the emergence of antibiotic-resistant bacteria. In the present work, the enzymes horseradish peroxidase and laccase from Trametes versicolor were evaluated for the conversion of triclosan in an aqueous matrix. The removal of antibacterial activity by the enzymatic processes was evaluated by an assay based on the growth inhibition of Escherichia coli K12. The horseradish peroxidase (HRP) process appears more advantageous than the laccase process in removing triclosan from an aqueous matrix, considering the reaction parameters pH, temperature, catalytic efficiency, and enzyme concentration. The highest conversion of triclosan catalysed by laccase was observed at pH 5.0, that is, lower than the typical pH range (6.5-7.5) of sewage treatment plants' effluents. The efficiency of laccase process was much more impacted by variations in the temperature in the range of 10-40°C. Kinetic studies showed that triclosan is a substrate more specific for HRP than for laccase. The protein content for the HRP-catalysed process was 14 times lower than that for the laccase process. Decay kinetics suggest that reaction mechanisms depend on enzyme concentration and its concentration. Both processes were able to reduce the antibacterial activity, and the residual activity of the treated solution is probably due to non-converted triclosan and not due to the reaction products. The laccase-catalysed conversion of triclosan in an environmental relevant concentration required a higher amount of enzyme than that required in the HRP process.