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B Environmental Distribution and Exposure
B.1.2 Water-Solid
K p = K oc × f oc =
c ad
c water
(B.2)
• K p : sorption coefficient, describes equilibrium between chemical sorbed to the
solid phase and chemical dissolved in water [L water/kg dry solid]
• K oc : partition coefficient between organic solid phase (as carbon) and water;
in the case of hydrophobic sorption, K oc [L water/kg organic carbon] can be
estimated from the octanol/water partition coefficient, K ow (log K oc = a ×
log K ow + b, where a and b are coefficients of the regression)
• f oc : fraction of organic carbon in soil solids [kg organic carbon/kg dry solid]
• c ad : concentration of adsorbed substance [mol/kg dry solid]
Note: For ionic substances, Eq. B.2 is not applicable. For the equilibrium distribution
of these substances, pH and ionic strength are important influencing factors.
B.1.3 Water-Biota
The concentration of a water-soluble substance in an aquatic organism can be
defined using a bioconcentration factor (BCF). As shown in Eq. B.3, the BCF can
be calculated (1) as a stationary concentration ratio between biota (e.g., fish) and
the surrounding water, as well as (2) a ratio between the respective uptake and
elimination rate constants within the organism. The BCF of a chemical is specific
for each organism and depends on the organism’s lipid content:
BCF =
c biota
c water
=
k water
k elim
(B.3)
• BCF: bioconcentration factor [L water/kg biota]
• c biota : concentration of substance in the biota [mol/kg biota]
• c water : concentration of substance in the surrounding water [mol/L]
• k water : pseudo first-order rate constant for uptake of a substance from water
[L water/kg biota/d]
• k elim : pseudo first-order rate constant for elimination of a substance from
organism [1/d]
Note: Equation B.3 is not valid for ionic and surface-active substances.
B.1.4 Internal Environmental Exposure
In addition to the bioconcentration factor (BCF) defined in Eq. B.3, the internal
exposure of an aquatic organism to a chemical can be further described by the
B Environmental Distribution and Exposure
B.1.2 Water-Solid
K p = K oc × f oc =
c ad
c water
(B.2)
• K p : sorption coefficient, describes equilibrium between chemical sorbed to the
solid phase and chemical dissolved in water [L water/kg dry solid]
• K oc : partition coefficient between organic solid phase (as carbon) and water;
in the case of hydrophobic sorption, K oc [L water/kg organic carbon] can be
estimated from the octanol/water partition coefficient, K ow (log K oc = a ×
log K ow + b, where a and b are coefficients of the regression)
• f oc : fraction of organic carbon in soil solids [kg organic carbon/kg dry solid]
• c ad : concentration of adsorbed substance [mol/kg dry solid]
Note: For ionic substances, Eq. B.2 is not applicable. For the equilibrium distribution
of these substances, pH and ionic strength are important influencing factors.
B.1.3 Water-Biota
The concentration of a water-soluble substance in an aquatic organism can be
defined using a bioconcentration factor (BCF). As shown in Eq. B.3, the BCF can
be calculated (1) as a stationary concentration ratio between biota (e.g., fish) and
the surrounding water, as well as (2) a ratio between the respective uptake and
elimination rate constants within the organism. The BCF of a chemical is specific
for each organism and depends on the organism’s lipid content:
BCF =
c biota
c water
=
k water
k elim
(B.3)
• BCF: bioconcentration factor [L water/kg biota]
• c biota : concentration of substance in the biota [mol/kg biota]
• c water : concentration of substance in the surrounding water [mol/L]
• k water : pseudo first-order rate constant for uptake of a substance from water
[L water/kg biota/d]
• k elim : pseudo first-order rate constant for elimination of a substance from
organism [1/d]
Note: Equation B.3 is not valid for ionic and surface-active substances.
B.1.4 Internal Environmental Exposure
In addition to the bioconcentration factor (BCF) defined in Eq. B.3, the internal
exposure of an aquatic organism to a chemical can be further described by the