Contaminant interactions, natural organic

In any particular system, some limited subset of these interactions is likely to dominate overall sorption behavior. In saturated subsurface systems, for example, most natural solid phases have only a weak affinity for hydrophobic organic compounds. It is frequently presumed for such systems that the characterization of one major sorption reaction, such as that between organic contaminants and natural organic matter associated with soils, sufficiently characterizes the overall process. Such an approach may be problematic for circumstances in which limited characterizations developed from one set of observations are extended to different system conditions, including different contaminant concentration ranges. 

Organic matter plays an important role in the binding of pollutants in natural environments. Several models are available to replicate the interaction of contaminants with natural organic matter. Nonideal competitive adsorption (NICA)-Donnan (ND) model is among the most popular ones. This model describes the interaction between cations and humic substances. ND is a... 

Chin, Y.-R, Weber, Jr., W.J. (1989) Estimating the effects of dispersed organic polymers on the sorption contaminants by natural solid, 1. A predictive thermodynamic humic substance-organic solute interaction model. Environ. Sci. Technol. 23, 978-984. 

Senesi, N. (1993a). Nature of interactions between organic chemicals and dissolved humic substances and the influence of environmental factors. In Organic Substances in Soil and Water Natural Constituents and Their Influence on Contaminant Behaviour, Beck, A. J., Jones, K. C., Hayes, M. H. B., and Mingelgrin, U., eds., Royal Society of Chemistry, London, UK, pp. 73-101. 

Kubicki, J.D. and Apitz, S.E., Models of natural organic matter interactions with organic contaminants, Org. Geochem., 30, 911, 1999. 

Asbestos fibers are nonvolatile and insoluble, so their natural tendency is to settle out of air and water, and deposit in soil or sediment (EPA 1977, 1979c). However, some fibers are sufficiently small that they can remain in suspension in both air and water and be transported long distances. For example, fibers with aerodynamic diameters of 0.1-1 pm can be carried thousands of kilometers in air (Jaenicke 1980), and transport of fibers over 75 miles has been reported in the water of Lake Superior (EPA 1979c). Adsorptive interactions between the fibers and natural organic contaminants may favor coagulation and precipitation of the fibers (EPA 1979c). 

The interaction between some organic contaminants and mineral surfaces has recently attracted attention as a way of cleaning up contaminants in natural waters. The large cation exchange capacity of smectite clay minerals (Section 4.5.2), in particular, has prompted research into their use as a catalyst, i.e. a substance that alters the rate of a chemical reaction without itself changing. Clay catalysts have potential applications as adsorbents to treat contaminated natural waters or soils. 

One research area that is certain to benefit from use of these facilities is the study of molecular-scale mechanisms of bioremediation and phytoremediation, where knowledge of the spatial distribution of contaminant species at the cellular level is critical for understanding reaction mechanisms and locations within or external to cells. Microfluorescence tomography is already beginning to yield this information in three dimensions at spatial scales of a few microns. Another growth area that will exploit X-ray microscopes is the characterization of natural organic matter and its interaction with mineral surfaces under in situ conditions. An X-ray microscopy study of fulvic acid in aqueous solutions at the ALS has already provided the first direct images of the macromolecular conformation of fulvic acid under in situ conditions (Myneni et al. 

The contaminants present in the aquatic environment consist of both inorganic and organic compounds. Their interactions with the colloidal, mineral and coated particle surfaces reflect the nature of these hydrophilic and lipophilic attractions. 

Metal ions in aerobic, natural waters, such as Cu % Fe, Mn % Mg +, and Ca, may catalyze hydrolysis of organic contaminants. Blanchet and St. George (1982), for example, showed that interaction of organophosphate esters with Cu and Mn led to the hydrolysis of pesticides. However, similar studies with Mg and Ca did not induce any transformation process. 

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