Environmental pH and ionic strength influence the electron-transfer capacity of dissolved organic matter

Abstract

Dissolved organic matter (DOM) plays an important role in the cycling of elements and the transformation of pollutants in the environment due to its electron-transfer capacity (ETC), but ETC may be affected by environmental factors such as pH and ionic strength. This study was aimed to reveal the effects of pH and ionic strength on the ETC of DOM and the possible mechanisms. DOM was prepared into solutions with various pH values (4, 6, 7, 8, and 10) and ionic strength (0.001, 0.01, 0.1, and 0.5 mol/L KCl). ETC of DOM including electron-accepting capacity (EAC) and electron-donating capacity (EDC) was determined with chronoamperometry. Spectroscopic and chromatographic properties of DOM were evaluated to obtain related structural information to explore the possible mechanisms for the ETC changes. Both the EAC and EDC of DOM increased consistently with increasing pH from 4 to 10. EAC and EDC increased with increasing ionic strength, peaked at 0.1 mol/L KCl, and then decreased. Gel permeation chromatogram displayed different molecular size distribution for the DOM in solution with different pH and ionic strength. Environmental pH and ionic strength influence the ETC of DOM by altering the conformation of DOM molecules.