**National Irrigation Water Quality Program**\
U.S. Department of the Interior

Evaluation of Toxicity to Larval Razorback Sucker of Selenium-Laden Food
Organisms from Ouray NWR on the Green River, Utah

Steven J. Hamilton, Kevin J. Buhl, Fern A. Bullard, and Susan F.
McDonald\
National Biological Service

EXECUTIVE SUMMARY

Many investigations have been conducted in recent years in an attempt to
determine what factors are causing the decline of threatened and
endangered fish such as razorback sucker. An on-site toxicity test was
conducted at Ouray National Wildlife Refuge, Utah, with larval razorback
sucker to determine the effects of dietary selenium on survival, growth,
and whole-body residues. Studies were conducted with 5, 10, 24, and
28-day old larvae fed food organisms collected from six sites. Site
water where organisms were collected had selenium concentrations ranging
from \<0.4 to 78 µg/L, and concentrations in food organisms ranged from
2.3 to 91 µg/g dry weight. Static renewal tests were conducted for 20 to
25 days using reference site water with selenium concentrations of \<1.1
µg/L. In all studies, nearly complete mortality occurred in 15 to 20
days. In study 4 with 28-day old larvae, fish weight was significantly
reduced in larvae fed organisms containing 12 µg/g selenium from
Sheppard pond 5 compared to pond 3. Whole-body concentrations of
selenium ranged from 3.7 to 14.3 µg/g in fish fed organisms from the
reference site (Sheppard Bottom pond 1) up to 94 µg/g in fish fed
organisms from North Roadside Pond. Limited information suggested that
the Sheppard pond 1 site was relatively clean and suitable as a
reference treatment. However, the nearly complete mortality of larvae
and elevated concentrations of selenium in larvae and selenium and other
inorganics in food organisms indicated this site was also contaminated
with selenium and other inorganics. Whole-body residues of selenium in
larvae and selenium concentrations in food organisms from all sites were
slightly lower or greater than thresholds where adverse effects occur in
other fish species. Larval razorback sucker seem to have a greater
sensitivity than other species that may have been due in part to the
presence of other inorganics in the reference water used in all
exposures or to inorganics such as vanadium that were elevated in food
organisms. Based on this study, selenium concentrations of 2.3 µg/g or
greater in food organisms, in combination with other elevated inorganics
in water and food organisms, may cause adverse effects in larval
razorback sucker. Evaluation of the enhancement or restoration potential
of nursery habitats for larval razorback sucker should incorporate
evaluation of contaminant concentrations in food organisms. Contaminant
evaluation is being considered as a vital part of screening floodplain
habitats for enhancement or restoration in the Upper Colorado River
Basin Recovery Program. This study suggests that bioaccumulation and
toxicity of selenium at low concentrations in food chain organisms, in
combination with other inorganics in water and food, can result in high
mortality of larval razorback sucker. Enhancement or restoration of
floodplain habitats would be of little value in the recovery of the
endangered razorback sucker in areas containing high concentrations of
contaminants.