Soil distribution

The toxic impurities of phosphorus ores are conserved in phosphorus fertilizers produced from these ores, and finally they are accumulated in the agroecosystems (see Chapter 13). These pollutants can enter into biogeochemical food webs and increase the ecological risk especially under acid soils distributed in many regions of the World (Europe, Asia and North and South America). 

Fly ash and bottom ash stored in open piles, chemicals spilled in handling, and soil distributed by construction activities will be carried in the runoff caused by precipitation events. 

Among these factors, organic content determines the soil distribution coefficient and is an important parameter that quantifies the distribution of organic pollutants in soil. The soil distribution coefficient (K. ) is the ratio between the mass of contaminant sorbed by soil (mg/g) to the mass of contaminant in the aqueous phase (mg/mL), or ... 

Residual and sedentary soils Residual soil is collected from the small, second order, drainage basin (< 100 km2) at a suitable site above its alluvial plain and base of slope, where alluvium and colluvium are respectively deposited. The residual soil may be developed either directly on bedrock or on till, as is the case in glaciated terrains. Residual soil distributed by agricultural activities should be avoided where possible since the top soil is usually affected by human activities. It is important to ensure that the material collected is residual and not transported material such as coluvium or alluvium. 

Table 8.9 Sequential 239,24opu leaching from a selection of Solway sediments and soil (% distribution, + Io counting errors) (McDonald et al., 1990)...

An octanol/water partition coefficient, log KQW, of 0.69 for aldicarb (42) gives a KQC of 3.1, so that the calculated soil distribution coefficient of 0.0155 indicates very little adsorption of aldicarb. Values for for the aldicarb oxides would be presumably much lower, i.e. these compounds would be sorbed even less by soil. 

Feller, C., Frossard, E. and Brossard, M. (1994) Phosphatase activity in low activity tropical clay soils distribution in the various particle-size fractions. Canadian Journal of Soil Science 74, 121-1 29. 

Soil Distribution Ratios, Ka, Kom> The sorption of nonpolar organic compounds on soil usually approximates a linear relation as illustrated in Figure 3.5 The slope of these lines defines a soil-water distribution ratio, K, which is expressed... 

Soil Organic Matter Organic compounds may exist in soil either in solution or the vapor phase and can be absorbed through the roots in either state, absorption from solution would be the most likely process. From the discussion of the sorption process in soil (see Sorption, Chapter 3) the concentration of the compound in aqueous solution, Caq, would be a function of the concentration in the soil (Csoii). and the soil distribution ratio, K, which in turn is dependent primarily on SOM content. One would predict that uptake would be inversely related to the level of SOM. Observations of the uptake of diel-drin by carrots raised in different soils provide an opportunity to evaluate this relation and demonstrate the dependence on the concentration of the compound in soil solution. If the uptake efficiency is defined by the ratio of the concentration of dieldrin in carrots to that in the soil it is clear that higher levels of soil organic matter reduce uptake by carrots (Table 5.6). The ATom for dieldrin is 6980 mL g from which values were calculated for dieldrin in each soil. Since = Cjoii/Caq the concentration of dieldrin in soil solution can be determined. If uptake is defined as Ccarrot/Caq consistent value... 

For organic chemicals not adsorbed by soils, distribution constant is equal to zero. 

Experimental and mathematical modeling studies were performed to evaluate the potential benefits and limitations associated with the use of nonionic surfactants to enhance the microbial transformation of hexachlorobenzene (HCB) by a dechlorinating mixed culture enriched from a contaminated sediment. In general. Tween series surfactants were shown to have little impact on methanogenesis, whereas, polyoxyethylene (POE) alcohols, Triton X-100 and SDS were found to strongly inhibit methanogenesis and HCB dechlorination. Subsequent experiments conducted with Tween 80 illustrated the ability of this surfactant to enhance the solubility of HCB and to reduce the HCB-soil distribution coefficient. Model simulations demonstrated, however, that the aqueous phase mass fraction of HCB was substantially reduced in micellar solutions, which corresponded with observed reductions in HCB dechlorination. These results indicate that the impacts of surfactants on both biological activity and contaminant phase distributions should be evaluated in order to accurately assess the potential for biotransformation of hydrophobic contaminants in the presence of surfactants. 

Figure 8. Simulated and measured values of the apparent HCB-soil distribution coefficient (K ) as a function of Tween 80 concentration and the HCB-monomer partition coefficient (K. Input parameters CMC = 35 mg/L b = 8.0 L/g = 5.99 g/kg Kj, = 403.4 L/kg = 0.0 Ldcg = 0.09 L/kg.

Soil distribution coefficient (solid/water concentration ratio)... 

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