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Mass transfer coefficients are estimated on the basis of empirical relationships
between organism wet weight, lipid content, and percentage of each prey item in
the diet. The model conservatively assumes that there is no loss of compound due
to metabolic transformation.
Information on the food chain of the management site is used to describe and
select typical organisms for use in the model.
Great Lakes Methodology for Predicting Fish Tissue
Concentrations from Water Concentrations.
The U.S. Environmental Protection Agency (EPA) has relied upon use of
steady-state bioconcentration factors (BCF) and bioaccumulation factors (BAF) to
relate water concentrations to the concentrations in fish tissue. A steady-state BCF
describes the ratio (L/kg) of a compound=s concentration in tissue to its
concentration in the surrounding water, when the organism is exposed in the
laboratory only through the water, by uptake through gill membranes or other
external body surfaces.
BCF = (g COC/kg wet wt tissue) = L/kg
(g COC / L water)
A steady state BAF describes the ratio (L/kg) the concentration of a substance
in tissue to its concentration in the surrounding water in situations where both the
organism and its food are exposed. BAF are typically based on field
measurements.
BAF = (g COC/kg wet wt tissue) = L/kg
(g COC / L water)
If lab or field measurements are unavailable, USEPA recommends that the
following methodology be used to derive BCFs and BAFs.
BCFs for organic compounds can be calculated from the octanol-water
partition coefficient, Kow, using the following relationship (Veith and Kosian
1983):
log BCF = 0.79 log Kow - 0.40
In the absence of a field measured BAF, USEPA recommends estimating
BAFs for organic compounds by multiplying the BCF by a factor which accounts
for the biomagnification of a pollutant through the food chain and lipid content of
the organism. As larger organisms, such as bluefish, consume other fish and
aquatic organisms, the concentration of some COCs are increased in the predator.
The factor which describes this biomagnification is called the food chain
multiplier (FCM). USEPA calculated FCMs that describe biomagnification
B2
Appendix B Food Chain and Toxicity Models
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