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Page Title: Bioaccumulation of COCs (Cont.)
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(b) Weight of the fish VF, kg.
(c) Rate of chemical transport in the aqueous phase of the gill Qw,
in units of L/day.
(d) Rate of chemical transport in the lipid phase of the gill QL, in
units of L/day.
The uncertainty associated with Qw and QL is expressed by the range
on the exponential term in the equation for Qw:
Qw = 88.3 VF 0.6 (+ 0.2)
(3)
QL = Qw / 100
(4)
Uncertainty in the uptake rates (QW and QL) will contribute to
uncertainty in fish body burden estimates and estimates of risk to
the fish and their consumers.
(2) Uptake from food. The rate at which fish take up chemicals from
food depends upon the food ingestion rate, the rate of diffusion of
the chemical across the intestinal wall, and the fecal egestion rate.
The Gobas model (1993) assumes that the efficiency with which
chemicals are taken up from food is related to the transport of
chemicals across aqueous and lipid phases of the gut:
1/ED = A Kow B
(5)
where
ED = the uptake efficiency from the diet (fraction)
A
= a constant relating to the transport rate of the chemical in the
aqueous phases of the fish
B
= a constant relating to the transport rate of the chemical in the
lipid phase of the fish
According to a nonlinear regression of available data, A is 5.3
(+ 1.5) 10-8), and B is 2.3 (+ 0.3). Uncertainty associated with
these estimates could contribute to uncertainty associated with
estimates of body burdens in fish and estimates of risk to the fish
and their consumers. The magnitude of uncertainty could be
evaluated by performing a sensitivity analysis on the input
parameters.
(3) Ingestion and elimination rates. The Gobas model (1993) expresses
the rate at which chemicals are eliminated through fecal egestion, as
the fecal elimination rate constant kE. Available data show that the
fecal egestion rate is approximately 3 to 5 times lower than the
ingestion rate. Therefore, the model assumes that
39
Chapter 5 Uncertainty in Tier IV Risk Assessments

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