  The occurrence of the extensively used herbicide diuron in the environment
poses a severe threat to the ecosystem and human health. Four different
ligninolytic fungi were studied as biodegradation candidates for the removal of
diuron. Among them, T. versicolor was the most effective species, degrading
rapidly not only diuron (83%) but also the major metabolite 3,4-dichloroaniline
(100%), after 7-day incubation. During diuron degradation, five transformation
products (TPs) were found to be formed and the structures for three of them are
tentatively proposed. According to the identified TPs, a hydroxylated
intermediate 3-(3,4-dichlorophenyl)-1-hydroxymethyl-1-methylurea (DCPHMU) was
further metabolized into the N-dealkylated compounds
3-(3,4-dichlorophenyl)-1-methylurea (DCPMU) and 3,4-dichlorophenylurea (DCPU).
The discovery of DCPHMU suggests a relevant role of hydroxylation for
subsequent N-demethylation, helping to better understand the main reaction
mechanisms of diuron detoxification. Experiments also evidenced that
degradation reactions may occur intracellularly and be catalyzed by the
cytochrome P450 system. A response surface method, established by central
composite design, assisted in evaluating the effect of operational variables in
a trickle-bed bioreactor immobilized with T. versicolor on diuron removal. The
best performance was obtained at low recycling ratios and influent flow rates.
Furthermore, results indicate that the contact time between the contaminant and
immobilized fungi plays a crucial role in diuron removal. This study represents
a pioneering step forward amid techniques for bioremediation of
pesticides-contaminated waters using fungal reactors at a real scale.
