Organism-environmental medium partitioning

Noting that the equilibrium concentration in each particular organic phase represented in the numerator of Eq. 10-3 can be divided by the concentration in the environmental medium, we can modify the equation using the respective partition coefficient between that organic phase and the environmental medium, A orgphasemed ... 

It may be deduced from KP = Koc x foc that partition coefficients of hydro-phobic organic compounds in general are dependent upon the chemical of interest (compound-specific properties affect the value of Koc) and the matrix properties of the medium in which it resides. In addition to the fraction of organic carbon present in the sorption phase, additional environmental factors affect partitioning. These factors include temperature, particle size distribution, the surface area of the sorbent, pH, ionic strength, the presence of suspended material or colloidal material, and the presence of surfactants. In addition, clay minerals may act as additional sorption phases for organic compounds. Nevertheless, organic carbon-normalized partition... 

Even if a chemical does not partition into an environmental medium, it may nevertheless undergo advective transport. For example, oil spilled at sea dissolves poorly in water, and most of it floats on the water s surface. The undissolved oil is transported advectively by the water, its pathways determined by wind, wave action, and ocean currents. Groundwater, too, may transport undissolved organic chemicals advectively, e.g., trichloroethylene that was spilled on the ground at an industrial site and percolated into a groundwater aquifer beneath the site. 

Bioconcentration refers to the passive partitioning of a xenobiotic between an abiotic environmental medium and a living organism. Bioaccumulation desaibes the uptake and retention of a xenobiotic from all sources, biotic (prey) as well as abiotic. Bioaccumulation depends on the same phenomenon as bioconcentration The rate at which an organism takes up a xenobiotic exceeds the rate at which the organism is able to eliminate it As a result, more chemical enters the body than leaves it per unit time. 

Octanol is a partitioning medium just as water is a partitioning media. While there is nothing inherently special about octanol with respect to other organic liquids, the extent that an organic chemical partitions to octanol from water has become a standard for evaluating hydrophobicity (i.e., chemicals that partition more to octanol from water are more hydrophobic). Since HOPs that are more hydrophobic accumulate more in body tissues, partition more strongly to soils and sediments, and are typically more easily removed by adsorption from water, the extent that HOPs partition to octanol from water is a very important environmental indicator. 

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