A widely used anti-inflammatory
drug, diclofenac (DCF), is recalcitrant
in many environmental compartments and poses threat to several aquatic
and terrestrial organisms. Enzymatic degradation of emerging contaminants
which are often micropollutants, has gained interest for the past
few years. However, production of enzymes often incurs high costs.
In this study, ligninolytic enzyme laccase was produced by white rot
fungi Tremetes versicolor (ATCC 20869) using agro-industrial
residues, apple pomace (AP), pulp and paper solid waste (PPSW), and
alfa fibers as substrates. Various known inducers for laccase production,
such as tween 80 (0.1% (w/w)), veratryl alcohol (3
mM Kg–1), CuSO4 (3 mM Kg–1), and phenol red (3 mM Kg–1) were used to enhance
laccase production. A maximum laccase activity of 49.16 ± 4.5,
52.4 ± 2.2, and 14.26 ± 0.8 U/gds (units/gram dry substrate)
was obtained from apple pomace, PPSW, and alfa plant fibers, respectively,
at optimal experimental conditions. Further, the kinetics of the laccase
mediated degradation of DCF was studied. At environmentally relevant
concentration of DCF (500 μg L–1), laccase-catalyzed
degradation followed first-order kinetics. At environmentally relevant
concentrations pH of 4.5 and temperature of 50 °C was found to
be optimal for the effective degradation of DCF with laccase. 3′-Hydroxydiclofenac,
4′-hydroxydiclofenac, and 5-hydroxydiclofenac were identified
as the major transformation products during the initial 5 h of degradation.
However, after 24 h of degradation, neither DCF nor any transformation
products were identified so that the proposed degradation mechanism
involved hydroxylation followed by ring opening and final mineralization
to CO2, NH3, and H2O and HCl.
