Roxarsone binding to soil-derived dissolved organic matter: Insights from multi-spectroscopic techniques

Area of Science:

• Environmental Chemistry
• Soil Science
• Biogeochemistry

Background:

• Roxarsone (ROX) is an organoarsenic feed additive with environmental implications.
• Soil-derived dissolved organic matter (DOM) ubiquitously influences the fate and transport of contaminants.
• Understanding ROX-DOM interactions is crucial for assessing its environmental behavior.

Purpose of the Study:

• To investigate the binding mechanisms and strength between roxarsone (ROX) and soil dissolved organic matter (DOM).
• To elucidate the role of DOM in the environmental fate of ROX in soil.

Main Methods:

• Fluorescence quenching titration and two-dimensional correlation spectroscopy (2D-COS) were used to study ROX-DOM binding.
• Fluorescence lifetime measurements and Fourier transform infrared spectroscopy (FTIR) revealed binding mechanisms.
• Excitation-emission matrix and synchronous fluorescence spectra identified DOM fluorophores.

Main Results:

• A high conditional stability constant (log KC = 5.06) indicated strong binding between ROX and DOM.
• 2D-COS elucidated the binding order: protein-like ≈ L-humic-like > S-humic-like fluorophores.
• FTIR and fluorescence lifetime data confirmed ROX interaction with hydroxyl, amide II, carboxyl, and other functional groups, forming stable complexes.

Conclusions:

• Dissolved organic matter (DOM) plays a significant role in the environmental fate of roxarsone (ROX) in soil.
• The strong binding suggests DOM can immobilize ROX, affecting its bioavailability and transport.
• Further research on DOM-ROX interactions is essential for accurate environmental risk assessment.