Natural organic carbon-water distribution

The early field studies revealed that elevated concentrations of fallout plutonium correlated with Increased concentrations of dissolved organic carbon. Experiments at Argonne National Laboratory corroborate this correlation the explanation Is probably that the organic compounds complex Pu(IV), and, hence, decrease the distribution ratio between water and sedlments(27). In these experiments the distribution ratio (Kj) between sediment and natural waters was measured as a function of DOC. Measurements of Kj In both field and laboratory experiments show an unmistakable effect of DOC upon the distribution ratio. Figure 4 shows the Inverse correlation between the K, of plutonium and concentration of DOC. 

Particle size distributions of natural sediments and soils are undoubtedly continuous and do not drop to zero abundance in the region of typical centrifugation or filtration capabilities. Additionally, there is some evidence to indicate that dissolved and particulate organic carbon in natural waters are in dynamic equilibrium, causing new particles or newly dissolved molecules to be formed when others are removed. Experiments with soil columns have shown that natural soils can release large quantities of DOC into percolating fluids [109]. 

Therefore, we may not be too surprised to find that nonionic chemicals show increasing solid-water distribution ratios for soils and sediments with increasing amounts of natural organic matter. This is illustrated for tetrachloromethane (carbon tetrachloride, CT) and 1,2-dichlorobenzene (DCB) when these two sorbates were examined for their solid-water distribution coefficients using a large number of soils and sediments (Fig. 9.7, Kile et al., 1995.)... 

All water sources may contain natural organic matter, but concentrations (usually measured as dissolved organic carbon, DOC) differ from 0.2 to more than 10 mg L l. NOM is a direct quality problem due to its color and odor, but more important are indirect problems, such as the formation of organic disinfection by-products (DBPs, e. g. M -halomethanes (THMs) due to chlorination), support of bacterial regrowth in the distribution system, disturbances of treatment efficiency in particle separation, elevated requirements for coagulants and oxidants or reductions in the removal of trace organics during adsorption and oxidation, etc. 

Newcombe, G., Drikas, M., and Hayes, R. (1997). Influence of characterized natural organic material on activated carbon adsorption II. Effect on pore volume distribution and adsorption of 2-methyhsobomeol. Water Res., 31, 1065—73. 

Cai, Y., Size distribution measurements of dissolved organic carbon in natural waters using ultrafiltration technique, Water Res., 33, 3056-3060, 1999. 

These data indicate that the tendency to distribute into the DOM varies both with the nature of the compound and the DOM. The soil humic acid was a more effective receptor and the magnitude of the Adom was directly related to the octanol-water partition coefficient, Aqw, which is also an index of a compound s tendency to distribute into a hydrophobic environment. Experiments with 1,2,3-trichlorobenzene (log Aqw = 4.14) and lindane (log = 3.70) did not give the same degree of solubility enhancement. Note that the distribution constant for DDT based on organic carbon, A[Pg.32]

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