Organic substances retardation factors

Table 4.6 gives a few representative values for Kow and Kp for non-polar organic substances on typical soil material and Table 4.7 gives estimates on typical retardation factors estimated for an aquifer. The data show that many non-polar organic substances, with the possible exception of very lipophilic substances such as hexachlorobenzene, are not markedly retarded in aquifers that contain little organic material (foe = 0.001 - 0.005). On the other hand, such substances are effectively retained in soils rich in organic carbon. 

Table 4.7 Estimated mean Retardation Factors for Organic Substances in the River-Groundwater Infiltration System of the Glatt River (Modified from Schwarzenbach et al., 1983)...

Action of Salts, Antiseptics, Alkaloids and of Other Organic Substances.—In the action of inorganic salts on peptonization, different factors must be considered. Certain salts precipitate albumin in great quantities but even before the quantity used is sufficient to produce predpitation, these already exert an effect on the albuminoid by changing its sensitiveness towards the proteolytic enzyme. The influence of the salts on the digestion is exerted in this case by an indirect method. It is not that the pepsin has been retarded, but rather that the protein substance has become less susceptible. Thus it is that in the presence of certain quantities of NaCl, pepsin with difficulty digests albumin, but a solution of pepsin with addition of sea salt appears very active after dialysis. 

Since mass transport calculations are in particular used for risk assessment of landfill liners and contaminated sites, some data are compiled in the following tables for mineral liners used in this field. In the literature, however, only a few investigations about the diffusion of organic substances are available for the typical soil or porous mineral materials used in landfills liners. In most cases only Da was determined. The effective diffusion coefficient can only be calculated from such data when the retardation factor is known for the respective soil material. 

The determination of R (see Eq. 7.25) by a measurement of the partition coefficient k in the laboratory, by some type of sorption experiment for the determination of adsorbed solid-phase concentration versus solution-phase concentration in equilibrium (so-called isopleths or isotherm), however, supplies values of R which are not comparable with the actual in field retardation factors in a mineral liner, because the specific surface susceptible to the pollutant is very different in both cases. Therefore, based on diffusion coefBcients in free aqueous solutions, the effective diffusion coefficients of organic substances for water-saturated mineral liners were estimated by using a tortuosity factor F= 1/3 (Muller et al. 1997a). Table 7.6 shows the results for various soil materials. 

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