Soil and sediment components

Aging effects. Diagenetic effects, which, apart from chemical processes (sorption, precipitation, occlnsion, incorporation in reservoir minerals and other geosorbents such as char, soot and ashes), involve enhanced mechanical consolidation of soil and sediment components by compaction, loss of water and mineral precipitations in the pore space, may induce a quite essential redaction of the reactivity of solid matrices (e.g. Lnthy et al., 1997). 

Cosolute effects the presence of further organic solutes, as is the case in real waters, may significantly alter the solubility of the individual compounds. Suspended organic matter soil and sediment components (e.g. humic acids) may result in increased apparent solubilities by serving as a sink compartment due to sorption processes. 

Suspended organic matter soil and sediment components (e.g. humic acids) may result in decreased bioavailability by serving as a sink compartment due to sorption processes. 

Rates of hydrolysis may be influenced by the presence of dissolved organic carbon, or organic components of soil and sediment. The magnitude of the effect is determined by the structure of the compound and by the kinetics of its association with these components. For example, whereas the neutral hydrolysis of chlorpyrifos was unaffected by sorption to sediments, the rate of alkaline hydrolysis was considerably slower (Macalady and Wolf 1985) humic acid also reduced the rate of alkaline hydrolysis of 1-octyl 2,4-dichlo-rophenoxyacetate (Perdue and Wolfe 1982). Conversely, sediment sorption had no effect on the neutral hydrolysis of 4-chlorostilbene oxide, although the rate below pH 5 where acid hydrolysis dominates was reduced (Metwally and Wolfe 1990). 

Xenobiotics exist not only in the free state but also in association with organic and mineral components of particles in the water mass, and the soil and sediment phases. This association is a central determinant of the persistence of xenobiotics in the environment, since the extent to which the reactions are reversible is generally unknown. Such residues may therefore be inaccessible to microbial attack and apparently persistent. This is a critical factor in determining the effectiveness of bioremediation (Harkness et al. 1993). Although the most persuasive evidence for the significance of reduced bioavailability comes from data on the persistence of agrochemicals in terrestrial systems (Calderbank 1989), the principles can be translated with modification to aquatic and sediment phases that contain organic matter that resembles structurally that of soils. 

Biological Mechanisms for Association with Organic Components of Soil and Sediment... 

All the preceding investigations have been concerned with polar compounds for which plansible mechanisms for their association with organic components of water, soil, and sediment may be more readily conceptualized. To provide a wider perspective, examples are given below for nentral compounds ... 

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. 

In addition, the removal of organic matter and Fe oxides from soils and sediments is common practice as a pretreatment for soils prior to physical, chemical and biological analyses. The effects of the removal of these components on physicochemical and surface chemical properties of soils will be discussed as well. 

The mobility of arsenic compounds in soils is affected by sorp-tion/desorption on/from soil components or co-precipitation with metal ions. The importance of oxides (mainly Fe-oxides) in controlling the mobility and concentration of arsenic in natural environments has been studied for a long time (Livesey and Huang 1981 Frankenberger 2002 and references there in Smedley and Kinniburgh 2002). Because the elements which correlate best with arsenic in soils and sediments are iron, aluminum and manganese, the use of Fe salts (as well as Al and Mn salts) is a common practice in water treatment for the removal of arsenic. The coprecipitation of arsenic with ferric or aluminum hydroxide has been a practical and effective technique to remove this toxic element from polluted waters... 

Chiou et al. (1998) attributed the enhanced partitioning of PAHs with respect to other HOCs to relatively high compatibility between the cohesive energy densities of PAHs and the aromatic components in SOM. However, the difference in Koc values between soils and sediments is related to the difference in polar group, rather than aromatic carbon, contents (Kile et al. 1999). The authors concluded that the content of polar groups (O-aryl and carboxyl C) has a large negative influence on Koc values, and hence on HOC sorption in soil and sediment. 

Seiber, N.J., S.C. Madden, M.M. McChesney, and W.L. Winterlin. 1979. Toxaphene dissipation from treated cotton field environments component residual behavior on leaves, and in air, soil and sediments determined by capillary gas chromatography. Jour. Agric. Food Chem. 27 284-290. 

In natural waters and soil and sediment systems one needs to distinguish analytically between dissolved and particulate material. Fig. 7.1 classifies various types of particulate and dissolved materials. Obviously, operational distinguishing (e.g., based on filtration or centrifugation) between "dissolved" and "particulate" matter merely by filtration is often not able to discriminate between particles and solutes, because size distribution of aquatic components vary in a continuous matter from Angstroms to microns. 

It is important to differentiate between two terms that are widely used in the literature, namely chemical kinetics and kinetics . Chemical kinetics is defined as the investigation of chemical reaction rates and the molecular processes by which reactions occur where transport (e.g., in the solution phase, film diffusion, and particle diffusion) is not limiting. On the other hand, kinetics is the study of time-dependent processes. Because of the different particle sizes and porosities of soils and sediments, as well as the problem to reduce transport processes in these solid phase components, it is difficult to examine the chemical kinetics processes. Thus, when dealing with solid phase components, usually the kinetics of these reactions are studied. 

Since TOC, for some solid wastes, was used as a criterion to measure leachate sorption for organic compounds, TOC by itself is considered as a single component system (i.e., SCS, see Sect. 2.1). To represent the SCS equilibrium system for various waste materials, the sorption characteristics of different soils and sediments were analyzed and evaluated using three different sorption iso-... 

Due to their lipophilic nature, PCBs tend to accumulate or reside in those environmental compartments that are non-polar and are amenable to lipid accumulation, such as the organic components of sediments. PCB presence in polar substances, such as water, is minimal. PCBs are not volatile and thus do not persist in air in any appreciable concentration. Therefore, the major sources of environment exposure to environmental species remain soils and sediments. 

Only a fraction of the total metal content of soils and sediments tends to be available for uptake by plants or biota. This fraction is generally associated with the colloidal material (i.e., clay minerals, hydrous oxides and organic matter), but views differ on the relative effects of the individual components. 

Radium in water may be readily adsorbed by sediments, soils, and aquifer components. It has been experimentally demonstrated that radium can be adsorbed by soils and sediments (Benes and Strejc 1986 Landa and Reid 1982), ferric hydroxide and quartz (Benes et al. 1984 Valentine et al. 1987), kaolinite and montmorillonite (Benes et al. 1985), and muscovite and albite (Benes et al. 1986). 

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