Imaging of Humic Substance Macromolecular Structures in Water and Soils

Abstract

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

Exploring How Organic Matter Controls Structural Transformations in Natural Aquatic Nanocolloidal Dispersions

“…Many complementary investigative techniques have been deployed including sedimentation (17), rheology (18b, 19a), electrokinetics (18b, 19a), imaging (16,25,26,27,28), and various forms of light scattering (20), particularly photon correlation spectroscopy (13,15,29). One unintentional consequence of the use of optical techniques (and indeed sedimentation and some atomic force microscopy) is that the length scales (ie, particle sizes) probed are typically hundreds to thousands of nm.…”

Binding of cationic surfactants to humic substances

“…The molar mass of FA particles is much smaller than that of HA particles and at a given pH the charge/g of FA is generally higher than that of HA. HA particles are often considered to be polydisperse and of amphiphilic nature [2,3]. Recent insights [4] also point to a micellar type of particle structure composed of sub-units.…”

Biological Formation of Organic Substances from Particulate Organic Matter

“…O 2 -• , H 2 O 2 and HO • ) along with reduction-oxidation (REDOX) reactions, global carbon cycle, nutrients cycle through degradation of its organic nitrogen or phosphorus , and finally a major source of energy to drive the aquatic ecosystem [4,7,8]. Allochthonous DOM originates from biological degradation of plant debris or root exudates and they includes fulvic and humic acids (humic substances), carbohydrates, phenols, organic acids, and so on [3][4][5][6]. Origin of allochthonous DOM from vascular plant materials is mostly regulated by the occurrence of three key factors [4]: (i) Physical functions (temperature and moisture); (ii) Chemical functions (nutrient availability, amount of available free oxygen and redox activity), and (iii) Microbial processes (microfloral succession patterns and availability of microorganisms (aerobic or anaerobic).…”