Four soil compartments

A first step in deciding on an analytical procedure to use or a species to look for is to understand that the species of interest may be in one of four soil compartments (see Figure 6.3) the solid (both inorganic and organic), the liquid (soil solution), the gaseous (soil air), or the biological (living cells). It is also important to remember that molecules and ions can move between compartments and interconvert between species. 

Before assessing how a chemical moves in the environment, the relevant media, or compartments, must be defined. The environment can be considered to be composed of four broad compartments—air, water, soil, and biota (including plants and animals)—as shown in Fig. 6.6. Various approaches to modeling the environment have been described.14-16 The primary difference in these approaches is the level of spatial and component detail included in each of the compartments. For example, the most simplistic model considers air as a lumped compartment. A more advanced model considers air as composed of air and aerosols, composed of species such as sodium chloride, nitric and sulfuric acids, soil, and particles released anthropogenically.17 A yet more complex model considers air as composed of air in stratified layers, with different temperatures and accessibility to the earth s surface, and aerosols segmented into different size classes.16 As the model complexity increases, its resolution and the data demands also increase. Andren et al.16 report that the simplest of models with lumped air, water, and soil compartments is suitable for... 

Results of the four compartment Fugacity Level 111 modeling show that all CPs are mainly associated with soils and sediments under the default conditions of the model, which assume 1,000 kg/h to air, water, and soil compartments. Although no emissions to sediments were assumed, sediments are a key compartment comprising 29-57% of emissions (Table 2). As expected, the % of CPs in the atmospheric compartment is small and declines with increased alkane chain length and chlorine content. 

Table 1.3 shows which of the four environmental compartments store significant amounts of the essential elements. Table 1.4 shows the estimated quantities of the elements that circulate rapidly through the environment—C, fixed N, P, S, and water. The amounts shown for the oceans are those above the thermocline, a temperature inversion at about 50 m depth, which separates the surface water from the deeper water. The soil is the largest reservoir of almost all the essential elements and is the only reservoir for most of the essential elements. 

Level I Model The components of a multimedia model are illustrated in the schematic (Fig. 10.10) with the four major compartments being, air, water, sediment, and soil. The equilibrium distribution of a fixed quantity of chemical among these compartments is defined by the Level 1 model, and by definition, the fugacities in each compartment would be equal... 

Mass balance relations can be derived for each of the four compartments where the input processes are balanced by intermedia transfer, advection, and degradation processes. These four equations provide an algebraic approach to the calculation of the four unknown fugacities that are compiled (Table 10.12) for emission at the rate of 1000 kg h into either the air, water, or soil compartment. 

The US Environmental Protection Agency s (EPA s) EPISuite software, for example, contains a Level III fugacity model based on Dr. Mackay s EQC model [65]. EPISuite allows the user to estimate how a chemical partitions between compartments and its overall persistence in the environment. The model represents four main compartments air, water, sediment, and soil. The software essentially solves a series of equations that represent advection... 

Figure 1.7.9 shows the distributions of mass and removal process rates for these four scenarios. Clearly, when benzene is discharged into a specific medium, most of the chemical is found in that medium. Only in the case of discharges to soil is an appreciable fraction found in another compartment, namely air. This is because benzene evaporates fairly rapidly from soil without being susceptible to reaction or advection. 

An integrated analysis of four different environmental compartments - SW, GW, SE, and soil - is performed applying MCR-ALS. The concentration of four different families of compounds - OCs, PAHs, pesticides, and alkylphenols (APs) -were analyzed during six different sampling campaigns (from year 2004 to 2006) at various locations distributed within the entire Ebro River basin. SW and GW were sampled twice a year, in spring and fall, whereas SE and soil were only sampled in fall. 

This section is divided in four parts describing the results obtained by the application of MCR-ALS to the analysis of the different environmental data matrices corresponding to various compartments Sect. 4.2.1, for SW (SWi and SW2 augmented matrices) Sect. 4.2.2, for surface and GW ([SW GW] augmented matrix) Sect. 4.2.3, for SE (SE augmented matrix) and Sect. 4.2.4, for SE and soil ([SE SO] augmented matrix). 

Phosphate must be applied as fertilizer to the soil. Ideally it is added in quantities sufficient to guarantee optimal yields, but not in excess in order to avoid P transportation into other compartments of the ecosystem. The amount added should be based on an accurate estimation of the plant-available fraction of P already present in a soil.This is an old and difficult task and a large number of extraction methods have been used since intensive land use was practised. Recently methods have been worked out in which a strip of filter paper impregnated with an Fe oxide (2-line ferri-hydrite) is dipped into a soil suspension and the amount of P adsorbed by the paper is taken as being plant-available (Sissingh,1988 Van der Zee et ah, 1987 Sharpley, 1993 Sharpley et ah,1994 Kuo and Jellum, 1994 Myers et ah 1997). Anion and cation resins extracted more P from four heavily fertilized soils than from goethite (Delgado Torrent, 2000). Other oxyanions adsorbed by soil Fe oxides are silicate, arsenate, chromate, selenite ( ) and sulphate. Adsorption of sulphate led to a release of OH ions and was substantially lowered once the Fe oxides were selectively removed (Fig.16.17). 

Indeed, OCPs, once released into the environment, are distributed into various environmental compartments (e.g., water, soil, and biota) as a result of complex physical, chemical, and biological processes. In order to perform appropriate exposure and risk assessment analyses, multimedia models of pollutant partitioning in the environment have been developed. Properties which are at the base of such a partitioning are water solubility (WS), octanol-water partition coefficient (Ko ), soil adsorption (K ), and bioconcentration factors (BCFs) in aquatic organisms, following these four equilibriums ... 

There are four main environmental sources of Hg (PNUMA 2005) (1) natural, (2) anthropogenic releases from mobilizing Hg impurities that exist in raw materials (e.g., fossil fuels and other ores), (3) anthropogenic releases from production processes, and (4) remobilization of Hg from soils, sediments, and water from past anthropogenic releases. Whatever the original source of Hg entry into the environment, the final receptors of such emissions are the atmosphere, aquatic ecosystems, soils, and biota. The biogeochemical cycle of Hg is complex in that several environmental compartments and processes are involved in the cycle. Estimates of Hg emissions to the atmosphere show that natural sources of Hg (median value... 

Several models of varying complexity have been developed to calculate and predict the distribution of chemicals in the environment (OECD, 1989a, 1993c). Most of them are derived from the Mackay model (Mackay 1979 Mackay and Paterson, 1981, 1982, 1990 Mackay, Paterson and Shiu, 1992) to estimate the environmental compartment (air, soil, water and biota) in which the chemical is most likely to be found. Based on the concept of fugac-ity, models were derived for four levels of increasing complexity. Level I... 

Hach of four Wet Chemistry Laboratories on the Phoenix Mars Lander shown at the opening of Chapter 6 was equipped with 23 electrochemical sensors, of which 15 were ion-selective electrodes similar to those discussed in this chapter. The robotic arm delivered soil through the sieve into the beaker compartment. Then aqueous solution was added to leach soluble salts from the soil. Sensors measured ions appearing in the liquid. 

It is convenient to define two evaluative environments and undertake calculations of chemical entry, transport, and transformations in these environments. The simplest approach is to define a four-compartment (or medium) system of air, water, soil, and sediment. Second is a more complex eight-compartment system (including aerosols, suspended sediment, and terrestrial and aquatic biota), which is more representative of real environments and is correspondingly more data-intensive. For a detailed discussion on these environments or unit worlds, the reader can consult Neely and Mackay (1982). The values and properties assigned to various environmental compartments or meia can be modified if chemical fate in a specific region is required. 

---