Radio-tracer experiments have shown that antimony, mercury and zinc interact to form complexes with humic and/or fulvic acids,
whose molar masses can be estimated by gel chromatography. Sb(III) and (V) humates are stable in the pH range 7–11, but are
largely dissociated below pH 4; humic acid does not reduce Sb(V) to Sb(III) in solution. Mercury forms a strong complex with
humic+fulvic acids. Zinc forms complexes with both humic acids and glycine, and the humic acid complex has similar elution
behaviour on dextran gel to a fraction from river water equilibrated with65Zn. At least one other form of zinc, in addition to Zn2+, occurs in this river.