Identification of copper binding sites in soil organic matter through chemical modifications and 13C CP-MAS NMR spectroscopy

Metal binding to an organic peat soil was probed by paramagnetic doping with copper, chemical modifications of the organic matter in the soil, and 13C CP-MAS NMR spin lattice relaxation rate measurements. Carboxyl and hydroxyl functional groups were determined to be most significant in copper uptake by the unmodified soil. Esterification and acetylation of the soil showed that metal binding by carbohydrate structures occurs independently of other functional groups and may even induce a pseudochelation phenomenon. Sorption isotherms corroborate the importance of carbohydrate structures in metal binding. These results suggest that environmental modeling of metal binding and retention in soils should incorporate estimates of the distributions of all functional groups in the soil organic matter (e.g. aliphatic, carbohydrate, phenolic, carboxyl) and their relative binding strengths.