Page 101 - The Toxicology of Fishes

Toxicokinetics in Fishes 81

100 R T

80 R
T
PERCENTAGE BOUND 60 T

40

20 R
R
T
0
-2 0 2 4 6 8

CHEMICAL LOG K OW
FIGURE 3.12 Chemical binding to plasma proteins as a function of chemical log K ow . The symbols (T) and (R) represent
values reported by Schmieder and Henry (1988) for trout and rat plasma proteins. Other symbols represent values summarized
by the authors: open squares, bovine serum albumin; open circles, rat plasma; open triangles, shark plasma; open diamonds,
human serum albumin. (Adapted from Schmieder, P.K. and Henry, T.R., Comp. Biochem. Physiol., 91C, 413–418, 1988.)

whole animal is low, this starvation-induced decrease in whole-body lipid content may cause chemical
concentrations in relatively lean tissues to increase substantially, even as whole-body chemical concen-
trations remain relatively constant (Gruger et al., 1975; Lieb et al., 1974).
Affinity considerations also determine the tissue distribution of lead during chronic exposures. In this
instance, the accumulation of lead occurs because of its structural similarity to calcium. In fish, as in
mammals, most of the accumulated lead is contained in bone (Camusso et al., 1995).

Lipid Mobilization and Xenobiotic Redistribution in Reproducing Fish
Female fish support egg development by mobilizing lipids from body stores. This lipid may be transferred
to the growing egg mass or incorporated into larger energy storage molecules such as vitellogenin.
Additional lipid may be mobilized in males and females to provide energy for spawning behaviors such
as migration and nest defense (Jobling et al., 1998). In either case, xenobiotics may redistribute from
fat storage depots to the developing gonads. To investigate this phenomena, Vodicnik and Peterson (1985)
exposed female yellow perch to [ C]-2,2′,5,5′-tetrachlorobiphenyl in water for 24 hours and then
14
monitored tissue distribution and elimination for 5 months. Two weeks after exposure, 30% of chemical
retained by fish was present in the developing ovaries. This value increased to 50% just prior to spawning,
which occurred 4 months into the study. Similar studies with rainbow trout demonstrated the redistri-
bution of [ C]-2,2′,5,5′-tetrachlorobiphenyl to eggs and sperm (Guiney et al., 1979). Developmental
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stage may be an important determinant of xenobiotic transfer to eggs. When steelhead trout were given
an intravascular dose of trifluralin (log K 5), little or no chemical was transferred to mature eggs
ow
(Schultz and Hayton, 1997).
The percentage of an accumulated lipophilic contaminant that is redistributed to the developing gonads
depends on several factors including: (1) the lipid content of the fish prior to gonad development, (2)
the fraction of whole-body lipid content that is mobilized and incorporated into the gonads, and (3)
the size of the gonads relative to total body weight. Niimi (1983) examined these features in five fish
species: rainbow trout, yellow perch, smallmouth bass, white bass, and white sucker. Yellow perch were
the leanest of these five species (5.1%) and transferred the greatest percentage of accumulated contam-
inants (25.5%) to their eggs. In contrast, rainbow trout had the highest starting lipid content (11.4%)
and transferred the lowest percentage of contaminants to their eggs (5.5%). The high percentage of