Enhanced removal of dibutyl phthalate in a laccase-mediator system: Optimized process parameters, kinetics, and environmental impact

Abstract

The persistence and recalcitrance of endocrine-disrupting chemicals (EDCs) in the environment have raised momentous concerns due to their carcinogenic, teratogenic, genotoxic, and cytotoxic effects on humans, animals, and plants. Unarguably, dibutyl phthalate (DBP) is one of the most ubiquitous EDCs because of its bioavailability in water, soil, and atmosphere. This study aims to investigate the efficiency of Agaricus bisporus laccase in the degradation of dibutyl phthalate (DBP) in laccase-mediator system. Here, enhanced removal efficiency was recorded during DBP degradation in laccase-mediator systems than in reaction medium containing laccase only. About 98.85% of 30 mg L^-1 DBP was efficiently removed in a medium containing 1.3 U mL^-1, 0.045 mM Syringaldehyde (SYR) at incubation temperature 30 ^aC and pH 5 within 24 h. This finding was further corroborated by the synergistic interplay of the optimal parameters in the laccase-SYR system done using response surface methodology (Box-Behnken Design). Furthermore, the addition of 1.5 mM of metal ions in the laccase-SYR system further promoted the enhanced removal of DBP in the following order: Cr³⁺> Pb²⁺> Ca²⁺> Al³⁺>Zn²⁺ > Cu²⁺. A significant decrease in DBP degradation was observed at higher concentrations of metal ions above 1.5 mM due to the inhibition of laccase active sites. The coefficient of correlation (R² = 0.9885) recorded in the Lineweaver bulk plot affirmed that the removal efficiencies are highly dependent on DBP concentration in the laccase-SYR system. The Gas-Chromatography Mass Spectrometry (GC-MS) analyses affirmed that the ortho-cleavage due to hydrolysis of DBP in the reaction system led to the formation of two metabolic degradation products (MBP and PA). The phytotoxicity assessment affirmed the detoxified status of DBP after treatment with significant improvement (90 and 91%) in the growth of Lens culinaris and Sorghum bicolor. This is the first report on DBP degradation in the laccase-SYR reaction system, underscoring the unique, eco-friendly, economical, and promising alternative to known conventional methods.

Keywords: Degradation; Dibutyl phthalate; Ecotoxicity; Laccase; Syringaldehyde.