20
2. Interpreting Selenium Concentrations
bioaccumulation occurs. Biomagnification of selenium (progressively
higher concentrations in successive trophic levels of the food chain) is
not clearly indicated in laboratory studies (Bennett et al. 1986, 1989,
1993). However, some field studies have found that the levels continue to rise from 2 to 6 times through the food chain in a pattern
suggestive of biomagnification (Woock and Summers 1984; Lemly
1985a, 1986; Saiki 1986a; Lemly and Smith 1987; Saiki and Lowe 1987;
Barnum and Gilmer 1988; Hothem and Ohlendorf 1989).
Field studies have documented selenium bioaccumulation factors of
500 to 35 000 in contaminated aquatic habitats where levels of waterborne selenium were in the 2 to 16 !lg SelL range (Sager and Cofield
1984; Woock 1984; Woock and Summers 1984; Lemly 1985a, 1985b;
Baumann and Gillespie 1986; Barnum and Gilmer 1988). These waterborne concentrations resulted in food-chain residues of 10 to 60 !lg Sel
g which, again, far exceed the dietary toxicity threshold for fish and
wildlife. Until about 1986, most of the published literature on selenium residues in aquatic food chains and associated impacts to predatory species pertained to fisheries in power plant cooling reservoirs in
the southeastern United States (eg, Duke Power Company 1980; Garrett
and Inman 1984; Woock and Summers 1984; Lemly 1985a, 1985b;
Gillespie and Baumann 1986). In these systems, it appeared that the
threshold for significant bioaccumulation was in the range of 2 to 5 !lg
SelL (Lemly 1985a, 1985b, 1986; Lemly and Smith 1987).
Several studies of selenium in agricultural irrigation drainwater in
the western United States show that selenium residues may accumulate to toxic levels (10-20 !lg Se/g) in the food chain when waterborne
concentrations are in the 0.5 to 3 !lg SelL range (Barnum and Gilmer
1988; Schroeder et al. 1988; Stevens et al. 1988; Hoffman et al. 1990;
Saiki 1990; Skorupa and Ohlendorf 1991; Hallock et al. 1992). This
may be due to the presence of ultra-trace amounts «1 !lg SelL) of
organoselenium compounds that bioaccumulate similar to free selenoamino acids and produce disproportionately high tissue residues as
compared to inorganic selenate and selenite (Besser et al. 1989, 1993).
In some cases, it may be the recycling of organic selenium contained
in decaying plant and animal detrital material that is responsible for
unexpectedly high residues in the food chain and in consumer species
of fish and wildlife (Saiki and Lowe 1987; Parker and Knight 1989;
Hallock et al. 1992; Sanders et al. 1992).
The environmental speciation of selenium is complex, and several
chemical forms are likely to be present in solution at a given location
and time (Cutter 1982, 1986, 1991; McKeown and Marinas 1986; Cooke
and Bruland 1987). However, the patterns and magnitude of
bioaccumulation are similar enough between aquatic systems impacted
by power production wastes, by agricultural irrigation drainwater, and
2. Interpreting Selenium Concentrations
bioaccumulation occurs. Biomagnification of selenium (progressively
higher concentrations in successive trophic levels of the food chain) is
not clearly indicated in laboratory studies (Bennett et al. 1986, 1989,
1993). However, some field studies have found that the levels continue to rise from 2 to 6 times through the food chain in a pattern
suggestive of biomagnification (Woock and Summers 1984; Lemly
1985a, 1986; Saiki 1986a; Lemly and Smith 1987; Saiki and Lowe 1987;
Barnum and Gilmer 1988; Hothem and Ohlendorf 1989).
Field studies have documented selenium bioaccumulation factors of
500 to 35 000 in contaminated aquatic habitats where levels of waterborne selenium were in the 2 to 16 !lg SelL range (Sager and Cofield
1984; Woock 1984; Woock and Summers 1984; Lemly 1985a, 1985b;
Baumann and Gillespie 1986; Barnum and Gilmer 1988). These waterborne concentrations resulted in food-chain residues of 10 to 60 !lg Sel
g which, again, far exceed the dietary toxicity threshold for fish and
wildlife. Until about 1986, most of the published literature on selenium residues in aquatic food chains and associated impacts to predatory species pertained to fisheries in power plant cooling reservoirs in
the southeastern United States (eg, Duke Power Company 1980; Garrett
and Inman 1984; Woock and Summers 1984; Lemly 1985a, 1985b;
Gillespie and Baumann 1986). In these systems, it appeared that the
threshold for significant bioaccumulation was in the range of 2 to 5 !lg
SelL (Lemly 1985a, 1985b, 1986; Lemly and Smith 1987).
Several studies of selenium in agricultural irrigation drainwater in
the western United States show that selenium residues may accumulate to toxic levels (10-20 !lg Se/g) in the food chain when waterborne
concentrations are in the 0.5 to 3 !lg SelL range (Barnum and Gilmer
1988; Schroeder et al. 1988; Stevens et al. 1988; Hoffman et al. 1990;
Saiki 1990; Skorupa and Ohlendorf 1991; Hallock et al. 1992). This
may be due to the presence of ultra-trace amounts «1 !lg SelL) of
organoselenium compounds that bioaccumulate similar to free selenoamino acids and produce disproportionately high tissue residues as
compared to inorganic selenate and selenite (Besser et al. 1989, 1993).
In some cases, it may be the recycling of organic selenium contained
in decaying plant and animal detrital material that is responsible for
unexpectedly high residues in the food chain and in consumer species
of fish and wildlife (Saiki and Lowe 1987; Parker and Knight 1989;
Hallock et al. 1992; Sanders et al. 1992).
The environmental speciation of selenium is complex, and several
chemical forms are likely to be present in solution at a given location
and time (Cutter 1982, 1986, 1991; McKeown and Marinas 1986; Cooke
and Bruland 1987). However, the patterns and magnitude of
bioaccumulation are similar enough between aquatic systems impacted
by power production wastes, by agricultural irrigation drainwater, and