Fulvic and humic acids isolated from groundwater : compositional characteristics and cation binding

Abstract Samples of humic substances were obtained from a waterworks at Fuhrberg, Germany. The material had a bimodal molecular size distribution with ∼40% of the total carbon in the 50,000–100,000-D (nominal molecular weight, NMW, in daltons) size fraction and ∼50% of the carbon in the 13 C NMR analyses indicating approximately even distribution among the two types. Competitive elemental binding studies indicated that Ca 2+ , Mg 2+ , Al 3+ and Fe 3+ do not effectively compete for copper binding sites on these compounds. In humic acids, these cations are predominantly bond by carboxylic groups.