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4.25.2  What is BCF? 

BIOCONCENTRATION the increase in concentration of a chemical in an organism resulting 

from tissue absorption levels exceeding the rate of metabolism and excretion. 

BIOCONCENTRATION FACTOR (BCF) used to describe the accumulation of chemicals in 

organisms, primarily aquatic, that live in contaminated environments. 

According to EPA guidelines, "the BCF is defined as the ratio of chemical concentration in the 

organism to that in surrounding water.  Bioconcentration occurs through uptake and retention of a 

substance from water only, through gill membranes or other external body surfaces.  In the 

context of setting exposure criteria it is generally understood that the terms "BCF" and "steady 

state BCF" are synonymous.  A steady state condition occurs when the organism is exposed for 

a sufficient length of time that the ratio does not change substantially.  

Bioconcentration factors (BCFs) are used to relate pollutant residues in aquatic organisms to the 

pollutant concentration in ambient waters.  The bioconcentration factor (BCF) is related to 

biomagnification effects.  Many chemical compounds, especially those with a hydrophobic 

component, partition easily into the lipids and lipid membranes of organisms and bioaccumulate.  

If the compounds are not metabolized as fast as they are consumed, there can be significant 

magnification of potential toxicological effects up the food chain.  The concern about 

bioaccumulation and biomagnification comes mainly from experience with chlorinated 

compounds, especially pesticides and PCBs, and their deleterious effects on vulnerable species, 

especially birds, frogs, and fish.  Only minimal experimental and monitoring information has been 

gathered on the bioaccumulation properties of many other currently used chemical compounds.  

In fact, the biomagnification of many widely available chemicals has not been observed or 

predicted in aquatic systems. 

BCF or BAF values are based on U.S. Environmental Protection Agency publications pursuant to 

Section 304(a) of the Federal Water Pollution Control Act as amended, literature values, or site 

specific bioconcentration data.  Current EPA guidelines for the derivation of human health water 

quality criteria use BCFs as well. 

BCFs are quantified by various procedures depending on the lipid solubility of the pollutant.  For 

lipid soluble pollutants, the average BCF is calculated from the weighted average percent lipids in 

the edible portions of fish and shellfish, which is about 3%; or it is calculated from theoretical 

considerations using the octanol/water partition coefficient. The BCF is calculated using the 

following equation: 

log BCF

.

0 76

log P

.

0 23

where logP is the octanol/water partition coefficient.  The   rule of thumb   is that a BCF value 

greater than 1000 poses a concern for bioaccumulation, particularly if the chemical is considered 

persistent in aquatic environments.  This BCF value corresponds to a logP of 4.3 or greater. 

For non lipid soluble compounds, the BCF is determined empirically.  The assumed water 

consumption is taken from the National Academy of Sciences publication Drinking Water and 

Health (1977). (Referenced in the Human Health Guidelines.) This value, of 2.0 liters/day, is 

appropriate as it includes a margin of safety so that the general population is protected.  The 6.5 

grams per day of contaminated fish and shellfish consumption value is the average per capita 

consumption rate of all (contaminated and non contaminated) freshwater fish and shellfish for the 

U.S. population.  

Although BCF assessments began as aquatic measurements, the exposure of plants and cattle 

to certain chemicals is also rated in terms of the bioconcentration factors. 

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