Bioaccumulation partition coefficient calculations

Inadequacy of Partition Coefficient Calculations in Evaluating Bioaccumulation... 

The dominant transport process from water is volatilization. Based on mathematical models developed by the EPA, the half-life for M-hexane in bodies of water with any degree of turbulent mixing (e.g., rivers) would be less than 3 hours. For standing bodies of water (e.g., small ponds), a half-life no longer than one week (6.8 days) is estimated (ASTER 1995 EPA 1987a). Based on the log octanol/water partition coefficient (i.e., log[Kow]) and the estimated log sorption coefficient (i.e., log[Koc]) (see Table 3-2), ii-hexane is not expected to become concentrated in biota (Swann et al. 1983). A calculated bioconcentration factor (BCF) of 453 for a fathead minnow (ASTER 1995) further suggests a low potential for -hcxanc to bioconcentrate or bioaccumulate in trophic food chains. 

Potential for bioaccumulation Due to their high Log values and high fat blood partition coefficient, the cyclic siloxanes are likely to be stored into the lipid tissue. However, bioaccumulation is not dependent just on the lipophilicity of the compound, but also in how fast it leaves the contaminated organism. Other indicators of bioaccumulation are the bioconcentration factor (BCF) and bioaccumulation factor (BAF). Values over 5,000 are usually characteristic for the bioaccumulative compounds. D4 has a BCF of 12,400 L/kg [293], D5 of 7,060 L/kg [279], and D6 of 1,160 L/kg [280], values calculated for fish. 

Dichlorobenzene is expected to bioconcentrate in aquatic organisms. The high octanol-water partition coefficient (K, ) value of 2,455 (Leo et al. 1971) also suggests that 1,4-dichlorobenzene has a moderate to high potential for bioaccumulation. A calculated bioconcentration factor (BCF) of 267 was reported for the fathead minnow (Pimephales promelas) (ASTER 1995). Measured mean BCF values of 370 and 720 were experimentally determined for rainbow trout exposed to water concentrations of... 

The logarithm of the n-octanol/water partition coefficient (log Kow is a useful preliminary indicator of the bioconcentration potential of a compound. The calculated log K values for 1,3-DNB and 1,3,5-TNB are 1.52 and 1.18 (Deneer et al. 1987), respectively, suggesting a low potential for bioaccumulation. An experimental bioconcentration factor (BCF) of 1,3-DNB for the guppy, Poecilia reticulata, was reported to be 74.13 (Deneer et al. 1987). This BCF indicates that bioaccumulation in aquatic organisms is not an important fate process. BCF data were not located for 1,3,5-TNB. 

The partition coefficient Kq of an organic compound in the 1-octanol/water system is used to assess the bioaccumulation potential and the distribution pattern of drugs and pollutants. The partition coefficient of imidazole and ILs strongly depends on the hydrogen bond formed by these molecules and is less than one due to the high solubility in water. The low value of the 1-octanol/water partition coefficient is required for new substances, solvents, insecticides to avoid bioaccumulation. Kqw is an extremely important quantity because it is the basis of correlations to calculate bioaccumulation, toxicity, and sorption to soils and sediments. Computing the activity of a chemical in human, fish, or animal lipid, which is where pollutants that are hydrophobic will appear, is a difficult task. Thus, it is simpler to measure the 1-octanol/water partition coefficient. This parameter is used as the primary parameter characterizing hydrophobisity. 

The organic carbon adsorption coefficient, is only applicable for individual substances. The K can generally be calculated from the octanoFwater partition coefficient, K. The following equation can be used log = 0.937 (log - 0.006. The log is determined in a laboratory without the use of organisms. It is a measure of how polar the substance is by determining whether the substance partitions primarily to water or to octanol. Substances that partition primarily to octanol are likely to bioaccumulate in the fat of organisms. 

Fig. 9.4. The new mixed model for metals in lakes. Load (or dose) parameters are related to the input of metals to the lake (direct load and load from the catchment), the metal amount in the lake water is distributed into dissolved and particulate phases by the partition coefficient (Kd). Sedimentation is net sedimentation per unit of time (the calculation unit is set to 1 year for Hg and 1 month for Cs). The sensitivity parameters influence biouptake of metals from water to phytoplankton (but they may also be used in other contexts, e.g., to influence the Kd-values, as illustrated by the dotted line, or the rate of sedimentation). The biological or ecosystem variables include pelagic and benthic uptake, bioaccumulation and retention time in the five compartments (lake water, active sediments, phytoplankton, prey and predator fish). The ejfect parameter is the concentration of the metal in predatory fish (used for human consumption). One panel gives the calculation of concentrations, another the driving parameters (model variables should, preferably, not be altered for different lakes, while environmental variables must be altered for each lake). The arrows between these two panels illustrate the phytoplankton biomass submodel...

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