Toxic Thresholds
23
should be applied uniformly to all aquatic systems when interpreting
selenium concentrations.
Aquatic Food Organisms of Fish and Wildlife
Although many laboratory and field studies have determined either
the toxicity or bioaccumulation of selenium in invertebrates and other
aquatic food organisms of fish and wildlife (see reviews by Eisler 1985;
Maier et al. 1988; Ogle et al. 1988; Ohlendorf 1989), very few have
done both and also report tissue residues associated with toxic effects.
Foe and Knight (1986) cultured the green alga Selenastrum capricornutum
in solutions of sodium selenite and found that Chlorophyll-a concentrations, dry weight, and cell replication were reduced when tissue
residues reached about 20
Se/g (Table 2.2). Cell division was completely stopped when residues reached the 100 to 500
Se/g range.
Kiffney and Knight (1990) exposed the cyanobacterium Anabaena flosaquae to solutions of sodium selenate, sodium selenite, and seleno-Lmethionine and found that Chlorophyll-a concentrations were
unaffected until tissue residues reached 700 J.ig Se/g regardless of the
chemical form of selenium used. Ingersoll et al. (1990) exposed the
cladoceran Daphnia magna to a 6: 1 ratio of waterborne sodium selenate and sodium selenite, and observed that residues of 20 J.ig Se/g or
greater were associated with reduced weight of adults. The production
of young was significantly reduced when tissue residues reached about
30 J.ig Se/g (Table 2.2).
Field studies show that benthic invertebrates and certain forage fishes
(mosquitofish Gambusia affinis, red shiners Notropis lutrensis, fathead
minnows Pimephales promelas) can accumulate 20 to 370 J.ig Se/g and
still maintain stable, reproducing populations (Woock and Summers
1984; Lemly 1985a, 1985b; Saiki 1986a, 1986b; Saiki and Lowe 1987;
Barnum and Gilmer 1988; Roth and Horne 1988; Schuler 1989; Schuler
et al. 1990). Plankton and aquatic plants appear to be largely unaffected with residues of 30 J.ig Se/g or more (Woock and Summers 1984;
Lemly 1985a; Saiki 1986a, 1986b; Roth and Horne 1988; Schuler et al.
1990).
The most important aspect of selenium residues in aquatic food chains
is not direct toxicity to the organisms themselves, but rather the dietary
source of selenium they provide to fish and wildlife species that feed on
them. The consensus of research studies is that most of the selenium in
fish tissues results from selenium in the diet rather than the water (Cumbie
and Van Horn 1978; Lemly 1982, 1985a; Finley 1985; Hamilton et al.
1986, 1990; Woock et al. 1987; Besser et al. 1993; Coyle et al. 1993). The
environmental selenium cycle includes strong bioaccumulation steps in
the aquatic food chain, and these bioaccumulation steps greatly increase
the dietary levels of selenium available to fish and birds that consume
23
should be applied uniformly to all aquatic systems when interpreting
selenium concentrations.
Aquatic Food Organisms of Fish and Wildlife
Although many laboratory and field studies have determined either
the toxicity or bioaccumulation of selenium in invertebrates and other
aquatic food organisms of fish and wildlife (see reviews by Eisler 1985;
Maier et al. 1988; Ogle et al. 1988; Ohlendorf 1989), very few have
done both and also report tissue residues associated with toxic effects.
Foe and Knight (1986) cultured the green alga Selenastrum capricornutum
in solutions of sodium selenite and found that Chlorophyll-a concentrations, dry weight, and cell replication were reduced when tissue
residues reached about 20
Se/g (Table 2.2). Cell division was completely stopped when residues reached the 100 to 500
Se/g range.
Kiffney and Knight (1990) exposed the cyanobacterium Anabaena flosaquae to solutions of sodium selenate, sodium selenite, and seleno-Lmethionine and found that Chlorophyll-a concentrations were
unaffected until tissue residues reached 700 J.ig Se/g regardless of the
chemical form of selenium used. Ingersoll et al. (1990) exposed the
cladoceran Daphnia magna to a 6: 1 ratio of waterborne sodium selenate and sodium selenite, and observed that residues of 20 J.ig Se/g or
greater were associated with reduced weight of adults. The production
of young was significantly reduced when tissue residues reached about
30 J.ig Se/g (Table 2.2).
Field studies show that benthic invertebrates and certain forage fishes
(mosquitofish Gambusia affinis, red shiners Notropis lutrensis, fathead
minnows Pimephales promelas) can accumulate 20 to 370 J.ig Se/g and
still maintain stable, reproducing populations (Woock and Summers
1984; Lemly 1985a, 1985b; Saiki 1986a, 1986b; Saiki and Lowe 1987;
Barnum and Gilmer 1988; Roth and Horne 1988; Schuler 1989; Schuler
et al. 1990). Plankton and aquatic plants appear to be largely unaffected with residues of 30 J.ig Se/g or more (Woock and Summers 1984;
Lemly 1985a; Saiki 1986a, 1986b; Roth and Horne 1988; Schuler et al.
1990).
The most important aspect of selenium residues in aquatic food chains
is not direct toxicity to the organisms themselves, but rather the dietary
source of selenium they provide to fish and wildlife species that feed on
them. The consensus of research studies is that most of the selenium in
fish tissues results from selenium in the diet rather than the water (Cumbie
and Van Horn 1978; Lemly 1982, 1985a; Finley 1985; Hamilton et al.
1986, 1990; Woock et al. 1987; Besser et al. 1993; Coyle et al. 1993). The
environmental selenium cycle includes strong bioaccumulation steps in
the aquatic food chain, and these bioaccumulation steps greatly increase
the dietary levels of selenium available to fish and birds that consume