The supramolecular structure of humic substances

The scientific understanding of the molecular size and shape of humic subst ances (HS) is critically reviewed. The traditional view that HS are polymer s in soil is not substantiated by any direct evidence but is assumed only o n the basis of laboratory experiments with model molecules and unwarranted results produced by incorrectly applying either analytical procedures or ma thematical treatments developed for purified and undisputed biopolymers. A large body of evidence shows an alternative understanding of the conformati onal nature of HS, which should be regarded as supramolecular associations of self-assembling heterogeneous and relatively small molecules deriving fr om the degradation and decomposition of dead biological material. A major a spect of the humic supramolecular conformation is that it is stabilized pre dominantly by weak dispersive forces instead of covalent linkages. Hydropho bic (van der Waals, pi-pi, CH-pi) and hydrogen bonds are responsible for th e apparent large molecular size of HS, the former becoming more important w ith the increase of pH. This innovative understanding of the nature of HS i mplies a further development of the science and technology for the control of the chemistry and reactivity of natural organic matter in the soil and t he environment.