Halogenated pesticide transformation by a laccase-mediator system

The transformation of organic halogenated pesticides by laccase-mediator system has been investigated. Twelve pesticides were assayed in the presence of nine different mediators. Acetosyringone and syringaldehyde showed to be the best mediators. The halogenated pesticides bromoxynil, niclosamide, bromofenoxim and dichlorophen were transformed by the laccase-syringaldehyde system showing catalytic activities of 48.8, 142.0, 166.2 and 1257.6 nmol min(-1) U-1, respectively. The highest pesticide transformation rates were obtained with a mediator-substrate proportion of 5:1, one of the lowest reported so far for the laccase-mediator systems. The analysis of the main product from the dichlorophen transformation showed that an oxidative dehalogenation is involved in the catalytic mechanism. Adduct formation between the mediator syringaldehyde and the pesticides dichlorophen or bromoxynil was also found after enzymatic oxidation. The main goal of this work is to evaluate environmental-friendly mediators for the pesticide transformation, and the potential of laccase-mediator system to efficiently reduce the environmental impact of organic halogenated pesticides is discussed. (C) 2009 Elsevier Ltd. All rights reserved.