| Thermodynamics and kinetics of copper complexation by Aldrich humic acid (HA) and dissolved organic matter (DOM) from several natural waters were studied. Toxicity tests used HA and Suwannee River DOM. Fractionated dissolved organic matter (DOM) from natural waters and the effluent of wastewater were characterized.; A two-site-discrete-ligand model describing copper complexation by HA or DOM is first-order in dissolved organic carbon (DOC) for 5–15 mg C/L. Increasing ionic strength or decreasing pH greatly increases Cu 2+ activity. Hardness has little effect at low concentration. Alkaline earth and copper compete for some binding sites. Cu-humate complex formation is rapid only in Ca-free solutions. A two-site kinetic model with pseudo-first-order rate constants was developed. Surface complexation of Cu by suspended solids was also modeled. Copper's reaction with suspended particles is faster than with the filtrate.; Copper toxicity to Ceriodaphnia dubia was determined in flow-through bioassays to investigate the effect of reaction kinetics. Cu toxicity decreases with increasing reaction time and humate concentration. Toxicity and Cu2+ concentration correlated, independent of humate concentration and reaction time, consistent with the free-ion activity model (FIAM). The chemical kinetic model, combined with bioassay system hydraulics, predicted Cu toxicity in the presence of HA or DOM. In the presence of solids, toxicity is the same for 6 and 24-h reaction times, indicating rapid equilibration. Correlation between survival and [Cu2+] also supports the FIAM, but deviation from results for bioassays of DOC is probably due to other effects of particles on the organisms.; Isolated humic acid (HA), fulvic acid (FA) and the hydrophilic fraction (HyI) were characterized by elemental analysis, 1H NMR spectrometry, proton and copper binding, and copper complexation kinetics. HA and FA from the four wetland waters have similar NMR spectra, total acidity and H/C ratios, corresponding to those in the literature. Aliphatic functional group contents follow HA < FA < HyI. Copper binding ability follows the carboxyl content: HyI < FA < HA. Copper complexation kinetics of HA and FA fractions of Suwannee River DOM are similar, but the rate with HyI is faster, implying that Cu reacts with weaker ligands faster than with stronger Cu-binding ligands. |
