Toxic Thresholds
27
selenium transferred to fish through aquatic food chains, and that 7 Ilg
Se/g be used as the threshold value for aquatic birds.
Fish Tissues
The salmonids are very sensitive to selenium contamination, and they
exhibit toxic symptoms even when tissue residues are quite low. In
laboratory studies, Hunn et al. (1987) exposed rainbow trout fry,
Oncorhynchus mykiss, to waterborne sodium selenite and found that significant mortality occurred when whole-body residues exceeded 4 Ilg
Se/g (parts-per-million). Hodson et al. (1980) and Hilton et al., (1980)
exposed juvenile rainbow trout to waterborne and dietary sodium selenite and found that significant changes in blood chemistry occurred
when whole-body tissue residues reached about 3 Ilg Se/g (liver tissues contained 12 Ilg Se/g). Survival was reduced when whole-body
residues exceeded 5 Ilg Se/g. Hamilton et al. (1986, 1989, 1990) exposed juvenile chinook salmon, Oncorhynchus tshawytscha, to combinations of waterborne and dietary selenium (6: 1 ratio of waterborne
sodium selenate and sodium selenite; field-source selenium diet; and
seleno-DL-methionine spiked commercial diet) and observed that
smoltification and seaward migration were impaired when wholebody tissue residues reached about 9.5 Ilg Se/g (Table 2.2). Mortality
occurred when concentrations exceeded 10 Ilg Se/g. However,
growth was impaired at whole-body tissue levels of only 2 to 3
Ilg Se/g; these levels were only 2 to 3 times those of the controls
(0.8-1.0 Ilg Se/g).
In studies of juvenile and adult fathead minnows, Pimephales promelas
(a cyprinid), Bennett et al. (1986) and Ogle and Knight (1989) reported that growth was inhibited at whole-body tissue levels of 6 to 8
Ilg Se/g or greater (selenium administered as waterborne sodium selenate and a dietary mixture of 25% sodium selenate, 50% sodium
selenite, and 25% seleno-L-methionine). Schultz and Hermanutz (1990)
dosed outdoor experimental streams with sodium selenite and observed
the effects on reproduction in fathead minnows. Reproductive success
(survival of fry to swim-up) was impaired when the ovarian tissue of
spawning females contained about 15 Ilg Se/g and resultant fry contained about 8 Ilg Se/g on a whole-body basis (Table 2.2).
Coughlan and Velte (1989) fed selenium-laden red shiners, Notropis
lutrensis, collected from a contaminated power plant reservoir to juvenile striped bass, Morone saxatilis (a percichthyid), and found that the
fish accumulated 14 to 16 Ilg Se/g in skeletal muscle tissue, did not
gain weight, and died within 78 days. There was also extensive tissue
damage in the liver and trunk kidney of these fish. Poor survival of
juvenile striped bass has been associated with whole-body tissue lev-
27
selenium transferred to fish through aquatic food chains, and that 7 Ilg
Se/g be used as the threshold value for aquatic birds.
Fish Tissues
The salmonids are very sensitive to selenium contamination, and they
exhibit toxic symptoms even when tissue residues are quite low. In
laboratory studies, Hunn et al. (1987) exposed rainbow trout fry,
Oncorhynchus mykiss, to waterborne sodium selenite and found that significant mortality occurred when whole-body residues exceeded 4 Ilg
Se/g (parts-per-million). Hodson et al. (1980) and Hilton et al., (1980)
exposed juvenile rainbow trout to waterborne and dietary sodium selenite and found that significant changes in blood chemistry occurred
when whole-body tissue residues reached about 3 Ilg Se/g (liver tissues contained 12 Ilg Se/g). Survival was reduced when whole-body
residues exceeded 5 Ilg Se/g. Hamilton et al. (1986, 1989, 1990) exposed juvenile chinook salmon, Oncorhynchus tshawytscha, to combinations of waterborne and dietary selenium (6: 1 ratio of waterborne
sodium selenate and sodium selenite; field-source selenium diet; and
seleno-DL-methionine spiked commercial diet) and observed that
smoltification and seaward migration were impaired when wholebody tissue residues reached about 9.5 Ilg Se/g (Table 2.2). Mortality
occurred when concentrations exceeded 10 Ilg Se/g. However,
growth was impaired at whole-body tissue levels of only 2 to 3
Ilg Se/g; these levels were only 2 to 3 times those of the controls
(0.8-1.0 Ilg Se/g).
In studies of juvenile and adult fathead minnows, Pimephales promelas
(a cyprinid), Bennett et al. (1986) and Ogle and Knight (1989) reported that growth was inhibited at whole-body tissue levels of 6 to 8
Ilg Se/g or greater (selenium administered as waterborne sodium selenate and a dietary mixture of 25% sodium selenate, 50% sodium
selenite, and 25% seleno-L-methionine). Schultz and Hermanutz (1990)
dosed outdoor experimental streams with sodium selenite and observed
the effects on reproduction in fathead minnows. Reproductive success
(survival of fry to swim-up) was impaired when the ovarian tissue of
spawning females contained about 15 Ilg Se/g and resultant fry contained about 8 Ilg Se/g on a whole-body basis (Table 2.2).
Coughlan and Velte (1989) fed selenium-laden red shiners, Notropis
lutrensis, collected from a contaminated power plant reservoir to juvenile striped bass, Morone saxatilis (a percichthyid), and found that the
fish accumulated 14 to 16 Ilg Se/g in skeletal muscle tissue, did not
gain weight, and died within 78 days. There was also extensive tissue
damage in the liver and trunk kidney of these fish. Poor survival of
juvenile striped bass has been associated with whole-body tissue lev-