Bioconcentration Factor (BCF) |
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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 efects. 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.
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 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.
The human daily intake of chemical compounds is estimated assuming
a "standard" daily intake of edible plants, meat, milk and drinking water. The chemical uptake in plants
takes place both via the soil and the air. The BCFs are calculated as function of logP only. The BCF for the plant
uptake via air is estimated to be of minor importance for chemicals present in sludge. It is primarily estimated
on the basis of the air-water partition coefficient of the chemical (which primarily depends on Henry's constant)
and logP.
The uptake of chemicals by cattle, which may result in unacceptable
concentrations in meat and milk, is characterized by the BCF calculated as a function of logP alone. In order
to estimate the concentration levels in cattle and plants, the concentration of the chemicals in soil and interstitial
water need to be known. Concentrations can be estimated on the basis of a general exposure model, and considerations
for single chemicals are generalized for chemical mixtures assuming linear behavior. A "safe" environmental
and hygiene risk assessment cannot be achieved by assessment only of a relative few of the many hundreds of chemical
residues contaminating, waste water, soil, etc., so much effort has been put into developing an exposure assessment
methodology sophisticated enough for chemical/physical well-defined fractions, which may be handled in accordance
with procedures for single chemicals.
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3. Svendsen C. Weeks JM. "Relevance and applicability of a
simple earthworm biomarker of copper exposure. I. Links to ecological effects in a laboratory study with Eisenia
andrei." Ecotoxicology & Environmental Safety. 36(1):72-9, 1997 Feb.
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5. Traas TP. Luttik R. Jongbloed RH. "A probabilistic model
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analysis." Ecotoxicology & Environmental Safety. 34(3):264-78, 1996 Aug.
6. Wang X. Harada S. Watanabe M. Koshikawa H. Sato K. Kimura T.,
"Determination of bioconcentration potential of tetrachloroethylene in marine algae by 13C." Chemosphere.
33(5):865-77, 1996 Sep.
7. Pant A. Srivastava SC. Singh SP. "Factors regulating methyl
mercury uptake in a cyanobacterium." Ecotoxicology & Environmental Safety. 32(1):87-92, 1995 Oct.
8. Makela TP. Oikari AO. "Pentachlorophenol accumulation in
the freshwater mussels Anodonta anatina and Pseudanodonta complanata, and some physiological consequences of laboratory
maintenance." Chemosphere. 31(7):3651-62, 1995 Oct.
9. Brown DG. Lanno RP. van den Heuvel MR. Dixon DG. "HPLC determination
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Larry N. Britton (CONDEA Vista Company, Austin, Texas), Surfactants
and the Environment, JSD 1,109-117 (1998).
Current EPA guidelines for the derivation of human health water
quality criteria - see
http://www.epa.gov/fedrgstr/EPA-WATER/1995/March/Day-23/pr-82.html and
http://www.epa.gov/fedrgstr/EPA-WATER/1997/August/Day-05/w20173.htm
http://www.epa.gov/fedrgstr/EPA-WATER/1998/April/Day-02/w8644.htm
http://www.fplc.edu/risk/vol4/summer/lakind.htm
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