Quantifying metal ions binding onto dissolved organic matter using log-transformed absorbance spectra

Area of Science:

• Environmental Chemistry
• Spectroscopy
• Geochemistry

Background:

• Dissolved organic matter (DOM) plays a crucial role in metal transport and bioavailability in aquatic systems.
• Understanding metal-DOM complexation is vital for predicting metal fate and ecological impacts.
• Existing methods for quantifying metal-DOM interactions can be complex and time-consuming.

Purpose of the Study:

• To introduce and validate novel spectroscopic parameters for quantifying heavy metal binding to DOM.
• To establish a sensitive and predictive method for assessing metal-DOM complexation at environmentally relevant concentrations.
• To correlate spectroscopic changes with metal-DOM binding extent using a differential approach.

Main Methods:

• Consistent examination of log-transformed absorbance spectra of DOM with increasing concentrations of Cu(II), Cd(II), and Al(III).
• Utilizing a differential approach to analyze spectral changes and highlight sensitive absorbance features.
• Introducing and calculating two parameters: change of spectral slope (DSlope325-375) and differential logarithm of absorbance (DLnA350).

Main Results:

• DSlope325-375 and DLnA350 parameters were strongly and unambiguously correlated with DOM-bound metal ion concentrations.
• These parameters effectively quantified Cu(II), Cd(II), and Al(III) binding across various pH, metal concentrations, and DOM types.
• NICA-Donnan model calculations corroborated the experimental findings.

Conclusions:

• The DSlope325-375 and DLnA350 parameters are predictive tools for quantifying in situ metal-DOM interactions.
• This approach offers a more efficient way to study DOM-metal complexation.
• The findings can help optimize existing models for metal-DOM complexation.