Application of a membrane model to the sorptive interactions of humic substances

• Published in: Environmental health perspectives Vol. 83; pp. 191 - 203
• Main Author: Wershaw, R.L. (U.S. Geological Survey, Arvada, CO)
• Format: Journal Article
• Language: English
• Published: United States National Institute of Environmental Health Sciences. National Institutes of Health. Department of Health, Education and Welfare 01.11.1989
• Subjects: 540320 - Environment, Aquatic- Chemicals Monitoring & Transport- (1990-); Acid soils; Adsorption; ANIONS; CATIONS; CELL MEMBRANES; CHARGED PARTICLES; CHEMICOPHYSICAL PROPERTIES; CHEMISTRY; CONTAMINACION DEL SUELO; ENVIRONMENTAL SCIENCES; FULVIC ACIDS; GEOLOGY; GROUND WATER; Humans; HUMIC ACIDS; Humic Substances; HUMUS; HYDROGEN COMPOUNDS; HYDROLOGY; IONS; MATHEMATICAL MODELS; MEMBRANAS CELULARES; MEMBRANE CELLULAIRE; Metal ions; Micelles; MODELE; MODELOS; Models, Molecular; Molecules; Monograph on Groundwater Quality; ORGANIC ACIDS; ORGANIC COMPOUNDS; Organic pollution; Organic soils; OXYGEN COMPOUNDS; P branes; POLLUTION; POLLUTION DU SOL; PROPIEDADES FISICO-QUIMICAS; PROPRIETE PHYSICO-CHIMIQUE; Sedimentary soils; Soil biochemistry; SOIL CHEMISTRY; SOIL CONTAMINATION; Soil Pollutants; SOIL POLLUTION; SOIL SORPTION; SORCION DEL SUELO; SORPTION; SORPTION DU SOL; SORPTIVE PROPERTIES; SURFACE PROPERTIES; WATER; Water Movements; WATER POLLUTION
• ISSN: 0091-6765; 1552-9924
• DOI: 10.1289/ehp.8983191

Humic substances, the dark-colored, natural organic polyelectrolytes that are found in practically all soils, sediments, and natural water, strongly interact with both inorganic and organic pollutants. Inorganic cationic species generally undergo complexation reactions with humic substances. The binding of cations, such as cupric ions, by humic substances often markedly reduces their toxicity to aquatic organisms. Some inorganic anionic species, in the presence of metal ions, are sorbed by humic substances. In these instances the metal ions appear to form bridges between the humic substances and the anions. Several different types of interactions take place between organic compounds and humic materials. Hydrophobic organic species partition into either insoluble or soluble humic substances. The insoluble humic substances will remove hydrophobic organic compounds from the aqueous phase, thereby rendering them less mobile. However, soluble humic substances will solubilize hydrophobic organics, increasing their mobility. Other types of interactions between humic substances and organic compounds, such as adsorption and ion exchange, also have been observed. These various interactions between humic substances and pollutants are important in governing their fate and movement in natural water systems, and, for this reason, a detailed understanding of the mechanisms of the interaction is important. A recently developed membrane model of the structure of humic substances is described; this model enables one to better understand the physical-chemical properties of these materials.