Imaging of humic substance macromolecular structures in water and soils

Humic substances (HSs) are the natural organic polyelectrolytes formed from the biochemical weathering of plant and animal remains. Their macromolecul ar structure and chemistry determine their role in biogeochemical processes . In situ spectromicroscopic evidence showed that the HS macromolecular str uctures (size and shape) vary as a function of HS origin (soil versus fluvi al), solution chemistry, and the associated mineralogy. The HSs do not simp ly form coils in acidic or strong electrolyte solutions and elongated struc tures in dilute alkaline solutions. The macromolecular structural changes o f HSs are likely to modify contaminant solubility, biotransformation, and t he carbon cycle in soils and sediments.