The bioconcentration factor

The exponential term (e kl) will approach zero and the concentration will reach a level (C J where uptake rate and elimination rate are the same when this happens, there is equilibrium. This is the philosophy behind introducing the term bioconcentration factor (BCF)  

For lipophilic substances this factor can be quite high, but theoretically, there will always be an equilibrium concentration, where no net uptake takes place. The factor is quite versatile as a simple parameter that describes the tendency of a substance to accumulate. 

Organic chemicals are often much more soluble in organic solvents and fats than in water and are said to be lipophilic. The BCF and also to a great extent the binding to soil are dependent on the lipophilic nature of the compound. In principle, this is simple to measure experimentally by shaking a small amount of the substance in a separating funnel with n-octanol and water. The two solvents separate into two phases, and the substance distributes between them. The distribution constant at equilibrium (KOW) is defined as 

Chromatographic methods using separation columns in which substances separate according to their lipophilicity are often used to determine the KOW. The retention times of the substances are compared to known standards. 

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Biomagnification along aquatic food chains may be the consequence of bioconcentration as well as bioaccumulation. Aquatic vertebrates and invertebrates can absorb pollutants from ambient water bottom feeders can take up pollutants from sediments. The bioconcentration factor (BCF) of a chemical absorbed directly from water is defined as... 

Veith GD, Delore DL, Bergstedt BV. 1979. Measuring and estimating the bioconcentration factor of chemicals in fish. Journal of the Fish Research Board of Canada 36 1040-1048. 

Bioconcentration Factor - Fish/Water (BCF). The partitioning of a chemical between water and fish is yet another expression of the hydrophobic nature of the chemical. The ratio of chemical in the fish to that in the water at equilibrium is defined as the bioconcentration factor. 

The bioconcentration factor, although usually related to fish is actually an estimate of the bioaccumulation potential for biota in general. Different organisms may bioconcentrate a given chemical to a lesser or greater degree, however with different chemicals, the relative ranking with respect to bioconcentration will be essentially the same for all species. 

By definition a bioconcentration in the organisms are relevant, if the bioconcentration factor (BCF) is higher than 100. 

Mytilus edulis) from the dissolved phase of seawater was predictable from the log of the bioconcentration factor and the log Kow of the congeners (Bergen et al. 1993). American oysters (Crassostrea virginica) from Galveston Bay, Texas, contained as much as 1100 pg/kg total PCBs DW soft parts, whereas conspecihcs from Tampa Bay, Florida, contained only 580 pg/kg DW soft parts most (54 to 94%) of the relative toxicity in both groups was due to PCBs 77,126, and 169 (Sericano et al. 1994). 

High hydrophobicity of pyrethroids is likely to result in their bioconcentration in biota which is mostly controlled by lipid content. On the other hand, the high hydrophobicity would reduce bioavailability of pyrethroids due to association with DOM and/or adsorption to suspended and bottom sediments [10]. The bioconcentration factor (BCF) from water to organisms is conveniently defined by... 

Chiou chose glyceryl trioleate (triolein) as model lipid because of its similarity to triglycerides which are abundant in organisms [109], Triolein is also a bulk lipid and the good correlation with the bioconcentration factor is restricted to neutral compounds of moderate hydrophobicity. No attempts were made to measure partitioning of ionogenic compounds with the glyceryl trioleate-water partition system. 

The major route for bioaccumulation of hydrophobic organic compounds in aquatic animals is passive diffusion over cell membranes. In fish, the gill epithelia are the predominant port of entry, with less than 40% of uptake across the skin [181]. Since permeability of the membrane is a direct function of the membrane-water partition coefficient and the diffusion coefficient across the membrane interior [182], the bioconcentration factor (logBCF) can be directly correlated with log K0Vl. or log Km%v for compounds with intermediate hydro-phobicity [183,184],... 

The determination of the bioconcentration factor (BCF) can be performed in two different ways computationally with quantitative structure activity relationship (QSAR) methods, or from experimental measurements [2], The QSAR methods estimate BCF from the structural or physicochemical properties of the compound, whereas the experimental methods use measured values of uptake and elimination rate constants or concentrations in the steady state. 

The concentration of carbon-14 residues in the different components of the model ecosystem is compared in Table The bioconcentration factor (BCF), defined as the ratio of the... 

Fig. 4). The initial uptake rate was similar for both types of samples, but the bioconcentration factor in the second instance was 4.0 (summer animals). 

Bromomethane is not expected to bioconcentrate in aquatic organisms because of its low octanol/water partition coefficient (K°w) (estimated to be about 13) (Callahan et al. 1979). The bioconcentration factor (BCF) for bromomethane has not been measured experimentally. However, based on an empirical relation between the BCF and the K°w (Neely et al. 1974), the estimated BCF for bromomethane is about 3. This low estimated BCF indicates that bromomethane should not significantly bioconcentrate (ERA 1986b). 

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. 

Bioaccumulation is generally referred to as a process in which the chemical concentration in an organism achieves a level that exceeds that in the respiratory medium (e.g., water for a fish or air for a mammal), the diet, or both. The extent to which chemicals bioaccumulate is expressed by several quantities, including the bioconcentration factor (BCF), bioaccumulation factor (BAF), biomagnification factor (BMF), and trophic or food web magnification factor (TMF) [6]. The ecological, biological and chemical parameters involved in the transfer and accumulation of contaminants in food webs are complex. 

In rainbow trout the bioconcentration factor (BCF) was dependent on water concentration (Oliver and Niimi 1983). At low concentrations of 0.10 ng/L a BCF of 5,800 was obtained, compared to a value of 17,000 obtained with higher water concentrations of 3.4 ng/L. Hexachlorobutadiene preferentially accumulates in the liver offish (Pearson and McConnell 1975). In mussels, the BCF was determined to be between 900 and 2,000 (Pearson and McConnell 1975). However, lower values were obtained for algae, crayfish, and bass (160, 60, and 29, respectively) (ERA 1976). The ERA is reviewing new BCF data and has recommended a value of 392 (EPA 1989a). 

Bioconcentration Factor in Aquatic Organisms. The bioconcentration factor (BCE) indicates the degree to which a chemical may accumulate in aquatic organisms, such as fish, clams, and zooplankton. It is given by the equation... 

Exposure Levels in Environmental Media. Environmental monitoring data are not available for soil and air, and the data available for water, sediments, and biota are not sufficient to determine ambient concentrations. These data would be helpful in determining the ambient concentrations of isophorone so that exposure estimates of the general population and the bioconcentration factor of this chemical in aquatic organisms can be made. 

In a variety of studies, it has been shown that organic pollutants associated with DOM are not bioavailable to aquatic organisms (e.g., Leversee et al., 1993 Traina et ah, 1996 Haitzer et ah, 1999). Hence, the bioconcentration factor, BCFiDOC, of a given compound i in the presence of DOM can be expressed by ... 

Because PAHs are hydrophobic, they tend to accumulate in lipids of organisms that are unable to metabolize them. There are several partition coefficients that can describe the accumulation of PAHs in organisms. Direct partitioning of aqueous phase PAHs to an organism is described by the bioconcentration factor ... 

In most cases we can assume that the equilibrium distribution and partitioning of organic chemicals in both mammalian and nonmammalian systems is a function of lipid content in the animal and that the lipid-water partition coefficient (AW) is equal to K0w Instances where this is not the case include specific binding sites (e.g., kepone in the liver) and nonequilibrium conditions caused by slow elimination rates of higher level organisms or structured lipid phases that sterically hinder accumulation of very hydrophobic chemicals. For aquatic organisms in constant contact with water, the bioconcentration factor or fish-water partition coefficient (AW) s simply ... 

The bioconcentration factor (BCF) is defined under conditions where the chemical reaches a steady-state (dCB / dt = 0) or when t in equation 14 is large, namely ... 

Gill uptake rate relationships. General relationships between the gill uptake rate constant (kj), gill elimination rate constant (k2), fecal egestion rate constant (kE), and the bioconcentration factor, based on chemical equilibrium (BCFeq) and on the truly dissolved chemical concentration in the water (BCFd) and the total chemical concentration in the water (BCFt), the field based bioaccumulation factor based on the truly dissolved chemical concentration in the water (BAF) and the octanol-water partition coefficient Kow. 

Hamelink et al. (1971) first proposed the hypothesis that bioconcentration is essentially a chemical partitioning process. Since then, several relationships between the bioconcentration factor and Kow have been reported. Meylan et al. (1999) reported the following correlation for 694 substances in fish ... 

Metabolic transformation of the absorbed substance by the organism results in a reduction in the BCF below the value that is expected from the chemical s ability to partition into the lipids of the organism s tissues. Figure 9.4 illustrates this by showing the bioconcentration factors of some metabolizable chlorodibenzo-p-dioxins together with those of a range of non-metabolizable substances. 

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