Cadmium Isotope Fractionation during Complexation with Humic Acid

Cadmium (Cd) isotopes are known to fractionate during complexation with various environmentally relevant surfaces and ligands. Our results, which were obtained using (i) batch experiments at different Cd concentrations, ionic strengths, pH values, (ii) modeling, (iii) infrared X-ray absorption spectroscopies, highlight the preferential enrichment of light bound humic acid (HA), leaving heavier pool preferentially in solution (?114/110CdHA–Cd(aq) ?0.15 ± 0.01‰). At high isotope fractionation mainly depends on its carboxylic sites. Outer-sphere occurs equilibrium together inner-sphere as well change first coordination hydration complexes solution. low nonspecific binding induced by electrostatic attractions plays a dominant role promotes complexation. This significant outcome elucidates mechanisms involved HA–Cd interactions. The results can be used fingerprinting available soil after solid or soluble natural organic matter evaluating contribution ligands phytoplankton-derived debris versus assimilation phytoplankton seawater.