Copper Safeguards Dissolved Organic Matter from Sunlight-Driven Photooxidation

Area of Science:

• Environmental Chemistry
• Aquatic Chemistry
• Biogeochemistry

Background:

• Sunlight drives the transformation of dissolved organic matter (DOM), impacting the aquatic carbon cycle.
• DOM photobleaching is a key process in sunlit aquatic environments.
• Understanding factors influencing DOM photobleaching is vital for aquatic ecosystem research.

Purpose of the Study:

• To investigate the effect of copper (Cu) on DOM photobleaching rates.
• To determine the role of phenolic moieties in DOM photodegradation.
• To quantify the impact of Cu on DOM electron-donating properties.

Main Methods:

• Simulated sunlight irradiation of DOM in the presence and absence of nanomolar Cu concentrations.
• Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) to analyze DOM composition.
• Development of a mathematical model to describe electron loss from DOM.

Main Results:

• Nanomolar Cu significantly decreased the photobleaching rate and loss of electron-donating moieties in DOM.
• Cu selectively inhibited the photooxidation of lignin- and tannin-like phenolic compounds within DOM.
• Phenolic moieties contribute at least 29-55% to DOM photobleaching (220-460 nm).

Conclusions:

• Copper acts as an inhibitor of DOM photobleaching, particularly affecting phenolic compounds.
• This study quantifies the significant contribution of phenolic structures to DOM photodegradation.
• Findings advance the understanding of DOM transformation processes in natural sunlit waters.