Clay, interaction with organic matter

Normally, because of the small size of soil particles and the presence of small capillaries and pores in the soil, the water phase is not totally independent of soil solid matter. Water present in larger spaces in soil is relatively more available to plants and readily drains away. Water held in smaller pores or between the unit layers of clay particles is held much more firmly. Water in soil interacts strongly with organic matter and clay minerals. 

In contrast to humic acids, proteins constitute a class of compounds that are chemically well defined, prevalent in soils, and able to form complexes with clay surfaces. Therefore, in order to study the interactions of anthropogenic chemicals with organic matter/clay complexes, we have started a series of MD simulations dealing with the adsorption of proteins by phyllosilicate surfaces. These investigations can be extended to humic acid coated clays, because many of the functional groups in proteins are the same as those in humic acids. 

The migration of explosives from surface soil to the water table is governed by their physicochemical properties and the mechanisms of their interaction with the soil matrix (mainly clay, and soil organic matter). The frequent detection of TNT (S = 140 mg/L) and RDX (S = 45 mg/L) in groundwater of contaminated sites is confirmed. As for HMX, its limited solubility in water (<5 mg/L) restricts its presence close to the soil surface. No field data is yet available on CL-20. 

A. S. Boyd and M. M. Mortland, Enzyme interactions with clays and clay-organic matter complexes. Soil Biochemistry, Vol. 6 (J.-M. Bollag and G. Stotzky, eds.), Marcel Dekker, New York, 1990, p. I. 

Carbonates, organic matter, Fe and Mn oxides, and clay minerals play important roles in controlling overall reactivity of trace elements in soils and sediments. This chapter addresses the interaction of trace elements with carbonates, organic matter, Fe and Mn oxides and clay minerals. Analytical techniques for trace element speciation in solid-phase and their distribution among various solid-phase components in arid and semi-arid soils are reviewed. Solubilities of trace elements in solid phases and their mineralogical characteristics in arid and semi-arid soils also are discussed. 

Carrizosa MJ, Hermosin MC, Koskinen WC, Cornejo J (2004) Interactions of two sulfonylurea herbicides with organoclays. Clays Clay Miner 52 643-649 Celis R, Hermosin MC, Cornejo J (2000) Heavy metal adsorption by functionalized clays. Environ Sci Technol 34 4593-4599 Chappell MA, Laird DA, Thompson ML, Li H, Teppen BJ, Johnston CT, Boyd SA (2005) Influence of smectite hydration and swelling on atrazine sorption behavior. Environ. Sci Technol 39 3150-3156 Chiou CT (1989) Theoretical considerations of the partition uptake of nonionic organic compounds by soil organic matter. In Sawhney BL, Brown K (eds) Reactions and movement of organic chemicals in soils. Soil Science Society of America, Madison, WI, pp 1-29... 

Bollag JM, LoU Ml (1983) Incorporation of xenobiotics in soil humus. Experentia 39 1221-1225 Bollag JM, Myers CJ, Minard RD (1992) Biological and chemical interactions of pesticides with soil organic matter. Sci Total Environ 123/124 205-217 Bolt GH (1955) Ion adsorption by clays. Soil Sd 79 267-278... 

---