Page 127 - The Toxicology of Fishes

Toxicokinetics in Fishes 107

Inhalation Exposure
Q W Effective Respiratory Q W
C EXP Volume C INSP

Q Q
C Cardiac Output C
C C
VEN ART

Adipose Tissue Q F
C VF Group C ART

Q × 0.4 Poorly Perfused Q
P P
C Tissue Group C
VP ART
Q × 0.6 C VP
P
Q K
Kidney
C C
VK ART
Q
Skin S
C C
VS ART
Dermal Exposure

Richly Perfused Q R
C Tissue Group C
VR ART

Q L
Liver
C VL C ART
C VGT
, V
K M Q
MAX GT
(metabolism, biliary Gut Tissues C
elimination) ART
C C
FOOD Gut Lumen FEC
Q Q
FOOD FEC
Dietary Exposure
FIGURE 3.22 Schematic representation of a physiologically based toxicokinetic model for fish. Q F , Q P , Q K , Q S , Q R , Q L ,
and Q GT refer to adipose tissue, poorly perfused tissue (white muscle, bone, and connective tissue), kidney, skin, richly
perfused tissue (stomach, upper intestinal tract, spleen, and gonads), liver, and lower intestine blood flows as proportions
of Q C , the cardiac output. Q W is the flow rate of inspired water that is available to exchange with blood at the gills, and
C INSP is the chemical concentration in this water. Q FOOD and Q FEC are the bulk flow rates of food and feces. C FOOD and C FEC
are the chemical concentrations in food and feces. C VF , C VP , C VK , C VS , C VR , C VL , and C VGT refer to chemical concentrations
in venous blood draining these tissues, and C VEN is the chemical concentration in mixed venous blood. K M and V MAX are
kinetic rate and capacity parameters for saturable metabolism in the liver.

where X is the amount of chemical in the compartment, Q is the arterial blood flow rate, C is the
i
i
a
chemical concentration in arterial blood and C is the chemical concentration in venous blood draining
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the compartment. By definition, the rate of chemical accumulation by a tissue cannot exceed the product
of blood flow rate and the chemical concentration in arterial blood. The actual rate of chemical accu-
mulation at any point in time depends on both the prior exposure history (i.e., the extent to which
chemical has already accumulated) and the rate of chemical exchange between blood and tissues, both
of which have the potential to impact C .
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