Deltamethrin degradation and effects on soil microbial activity.

Area of Science:

• Environmental Chemistry
• Soil Science
• Microbiology

Background:

• Pesticide persistence and degradation are crucial for environmental risk assessment.
• Understanding deltamethrin's fate in soil is vital for agricultural and ecological safety.

Purpose of the Study:

• To investigate the degradation pathway and microbial interactions of deltamethrin in two Egyptian soils.
• To identify the metabolites formed during deltamethrin's breakdown under aerobic and anaerobic conditions.

Main Methods:

• Laboratory incubation of ¹⁴C-labelled deltamethrin in two soil types (10 mg/kg) for 90 days.
• Monitoring of extractable and bound ¹⁴C-residues, evolved ¹⁴CO₂, and microbial activity.
• Chromatographic analysis (HPLC) to identify methanol-soluble residues and metabolites.

Main Results:

• Deltamethrin showed a decrease in extractable residues and an increase in bound residues over time.
• ¹⁴CO₂ evolution increased under both aerobic and anaerobic conditions.
• The inhibitory effect of deltamethrin on soil microorganisms decreased with incubation time.
• Four primary metabolites were identified: 3-(2',2'-dibromovinyl)-2,2-dimethylcyclopropane carboxylic acid, 3-phenoxybenzaldehyde, 3-phenoxybenzoic acid, and 3-phenoxybenzyl alcohol.

Conclusions:

• Deltamethrin undergoes degradation in Egyptian soils, forming bound residues and CO₂.
• Microbial activity plays a role in deltamethrin's transformation, with its inhibitory effect diminishing over time.
• Identification of key metabolites provides insights into the degradation pathways and potential environmental impact.