PCDD/F formation from chlorophenols by lignin and manganese peroxidases

Area of Science:

• Environmental Chemistry
• Biotechnology
• Organic Chemistry

Background:

• Polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/F) are persistent organic pollutants.
• Sewage sludge composting can be a source of PCDD/F.
• Ligninolytic enzymes like lignin peroxidase (LiP) and manganese peroxidase (MnP) are present during composting.

Purpose of the Study:

• To investigate the in vitro formation of PCDD/F using chlorophenol mixtures and lignolytic enzymes.
• To compare PCDD/F concentrations with controls and assess the impact of different enzymes and conditions.
• To explore potential biogenic pathways for PCDD/F formation during sewage sludge composting.

Main Methods:

• In vitro study using two chlorophenol mixtures (di+tri and tri+tetra+penta chlorophenols).
• Incubation with two lignolytic enzymes: lignin peroxidase (LiP) and manganese peroxidase (MnP).
• Analysis of PCDD/F concentrations in final samples and comparison with initial chlorophenol content.

Main Results:

• Manganese peroxidase (MnP) with phosphate buffer caused a significant increase in PCDD/F, particularly OCDD, from 1·10(7) to over 8·10(8) ng kg(-1) chlorophenol.
• Lignin peroxidase (LiP) at 37°C showed a moderate increase in OCDD, from 1.3·10(7) to 2.6·10(7) ng kg(-1) chlorophenol.
• Observed PCDD/F increases align with literature findings for composting processes, suggesting biogenic formation.

Conclusions:

• MnP is a key enzyme in the significant formation of PCDD/F during simulated composting conditions.
• LiP contributes to PCDD/F formation, but to a lesser extent and under specific temperature conditions.
• The study supports the hypothesis of biogenic PCDD/F formation during sewage sludge composting, though its contribution to overall toxicity may be limited.