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RATIONALE

Dyes have been widely used to accentuate or to provide different colors to foods. However, the high concentrations of dyes in effluents from the food industries can cause serious and unpredictable damages to aquatic life in general. Furthermore, since conventional biological treatments have been shown to be ineffective, the use of advanced oxidation processes to promote the depletion of such dyes in water bodies has turned out to be mandatory.

METHODS

The degradation of the food dye Brilliant Blue by ozone in aqueous solution is reported herein. The overall process was monitored in real time by using direct infusion electrospray ionization high-resolution mass spectrometry in the negative ion mode, ESI(−)-HRMS.

RESULTS

Preliminary results (visual inspection and UV–vis spectra) showed the high efficiency of ozonation in causing the decoloration of an aqueous solution of the dye whereas TOC (total organic carbon) measurements revealed that such an oxidation process was unable to promote its complete mineralization. ESI(−)-HRMS data showed that the substrate consumption occurred concomitantly with the appearance of four by-products, all of them produced by an initial attack of hydroxyl radicals (generated via the decomposition of ozone) on the two imino moieties of the dye molecule. Structures were proposed for all the by-products based mainly on the high-resolution mass measurements and on the characteristic reactivity of typical functional groups towards hydroxyl radicals. An unprecedented degradation route of Brilliant Blue by ozone in aqueous solution could thus be proposed.

CONCLUSIONS

A greater ecotoxicity against Artemia salina was observed for the by-products than for the original dye. This indicates that the identification of by-products arising from oxidation treatments is of primary importance since such compounds can be more hazardous than the precursor itself. Copyright © 2012 John Wiley & Sons, Ltd.