Complexation of Copper Algicide and Cellular Organic Matter: Implications for Its Fate in Algae-Laden Surface Waters

Copper-based algicides have been widely used to suppress cyanobacterial biomass. Constrained by the heterogeneous characteristics of cellular organic matter (COM) in aquatic ecosystems, little information on the Cu(II) binding of different COM subfractions has been obtained. In this study, the original COM solution was divided into four fractions, the hydrophobic (HPO), transphilic (TPI), charged hydrophilic (CHPI), and neutral hydrophilic (NHPI) fractions, via resin-mediated fractionation. A comprehensive methodology that integrates two-dimensional correlation spectroscopy (2DCoS), hetero-2DCoS, and moving-window 2DCoS analysis was used to identify the binding sites and binding sequence of COM subfractions in response to Cu(II) perturbation. The most sensitive groups in the HPO, TPI, CHPI, and NHPI fractions were aryl υ_C–H, aliphatic δ_C–H, amide II υ_C–N, and polysaccharide ν_C–O, respectively. Each subfraction could interact with Cu(II) through diverse functional moieties, and carboxylic, aliphatic, aryl, and phenolic groups were the basic units of COM chromophores. The functional groups could coordinate with Cu(II) when it was present at both trace and high concentrations, but the abundance of functional groups varied significantly among COM subfractions and even chromophores. These findings enhance our understanding of the molecular characteristics of Cu(II) complexes and the environmental fates of metal–organic complexes in aquatic systems.