7821

• UCREFRP Catalog Number: 7821
• Author: Hamilton, S. J., et al.
• Title: Evaluation Of Toxicity To Larval Razorback Sucker Of Selenium-Laden Food Organisms From Ouray NWR On The Green River, Utah.
• USFW Year: 1996.
• USFW - Doc Type: \
• Copyright Material: NO

fed brine shrimp nauplii during typical fish culture operations had been observed, and brine
shrimp can contain as much as 2.7 j-lg/g selenium. this concentration in aquatic invertebrates. by
itself and in the absence of other biological. chemical. or physical stressors, is probably not
sufficient to cause adverse effects in larval fish. This suggests that in the present investigation
the adverse effects observed in studies 2, 3, and 4 in larvae fed food organisms from S I
(selenium concentrations of2.3 and 2.5 j-lg/g) or S-l (selenium concentration of2.4 j-lg/g) may
not have been due to selenium alone. but rather to the mixture of inorganics, including selenium.
in the food organisms or S 1 water. Adverse effects observed in the other treatments and in fish
fed food organisms from S 1 and S4 that contained 3.5 /-lg/g or more of selenium probably was
due primarily to selenium.

There was a substantial decrease in selenium concentrations in older larvae (24-28 day
old at test initiation) in study 3 and 4 compared to concentrations in younger larvae in study
2 (lO-day old at test initiation). Although selenium concentrations in zooplankton from
various sites decreased slightly in studies 3 and 4 compared to study 2, the decrease was too
small to account for the relatively large decrease in fish residues. Bennett et al. (1986)
reported a somewhat similar response in fathead minnow larvae fed selenium-laden rotifers.
They found 9-day old larvae accumulated selenium concentrations of 61 p.g/g after 7 days
exposure, whereas 17-day old larvae accumulated only 52 p.g/g after 9 days exposure. Even
though the test with 17 -day old larvae was 2 days longer, they accumulated less selenium,
and the authors suggested that the increase of larvae weight decreased the tissue
concentrations of selenium. Part of the reason for the different whole-body residues may be
due to body size, which affects kinetic rate constants for chemical uptake, and the
concomitant dramatic differences in surface area/volume ratios between organisms of
different size (Rand et al. 1995).

Selenium concentrations of 4 p.g/g or more in whole-body of young fish exposed
through dietary or waterborne exposures have been associated with adverse effects (Table
14). Although some of the waterborne exposures may seem high, the main point of Table 14
is the values for whole-body residue and the resulting adverse effect. From Table 14,
waterborne exposure requires higher selenium exposure concentrations than dietary exposures
to generate similar whole-body residues. However, once whole-body selenium reach a
certain concentration (i.e., 4 p.g/g), regardless of exposure route, adverse effects will occur.
Based on the literature given in Table 14 and others, Lemly (1993) recommended that whole-
body residues of selenium in fish of 4 p.g/g, regardless of exposure route, be taken as the
toxic threshold for adverse effects. This threshold was exceeded in 5 out of the 8 residues in
larval razorback suckers in the Ouray study (Table 10). The other three residues were 3.6,
3.7, and 3.9 p.g/ g, which if rounded would equal the proposed threshold for toxic effects of
selenium in fish. Thus, it seems that larval razorback sucker are as sensitive as the three
species, i.e., rainbow trout (Oncorhynchus mykiss), chinook salmon (Oncorhynchus
tshawvtscha), and bluegill, with the lowest whole-body residues of selenium associated with
adverse effects (Table 14).

The whole-body concentrations in larval razorback sucker were from zooplankton

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