52
3. Toxic Effects of Selenium in Fish
Persistence of Impacts
In response to concerns about the fishery problems in Belews Lake,
the electric utility company switched to a dry-ash handling system
that disposed the waste in a landfill rather than a wet basin. By late
1986, selenium-laden wastewater no longer entered the lake (North
Carolina Department of Natural Resources and Community Development [NCDNRCD] 1986), and in subsequent years a stocking program
was successful in re-establishing adult populations of sport fish (eg,
centrarchids such as largemouth bass, Micropterus salmoides, and bluegill, Lepomis macrochirus). Follow-up studies were conducted in 1996 to
assess recovery of the ecosystem in Belews Lake (Lemly 1997). Tissue
selenium concentrations and associated impacts to fish were measured
and compared to pre-1986 conditions to determine how much change
had occurred since selenium inputs stopped. Findings were also examined using a hazard assessment protocol (see Chapter 4) to determine
if ecosystem-level hazards to fish and aquatic birds had changed as
well.
Results showed that waterborne selenium fell from a peak of 20 J.1g
SelL before 1986, to less than 1 J.1g SelL in 1996; concentrations in
biota were 85 to 95% lower in 1996. Hazard ratings indicated that high
hazard existed prior to 1986, and moderate hazard was still present in
1996, primarily due to selenium in the sediment-detrital food pathway. Concentrations of selenium in sediments fell by 65 to 75% during the period but remained sufficiently elevated (1-4 J.1g Se/g) to
contaminate benthic food organisms of fish and aquatic birds. Field
evidence confirmed the validity of the hazard ratings. Developmental
abnormalities in young fish persisted in 1996, indicating that selenium-induced teratogenesis and reproductive impairment were still
occurring a decade after selenium inputs stopped. Moreover, the residuallevels of selenium were sufficient to cause seasonal mortality in
young bluegill and other centrarchids because of Winter Stress Syndrome (see next section in this chapter), further impeding the recovery of fish populations. The latent effects occurred because of selenium
present in sediments, which was mobilized gradually, yet continually,
through the detrital food chain and accumulated to toxic levels in fish
tissues. Impacts to reproduction and overwinter survival of young fish
persisted, even though adult populations were re-established through
a stocking program. Projections indicate that several more decades may
be necessary for the Belews Lake ecosystem to fully recover (Lemly
1997). The low inflow of water and long retention time (volume replacement time about 1500 days), combined with low productivity (oligotrophic), tend to reduce natural flushing and enhance recycling of
selenium within the reservoir.
3. Toxic Effects of Selenium in Fish
Persistence of Impacts
In response to concerns about the fishery problems in Belews Lake,
the electric utility company switched to a dry-ash handling system
that disposed the waste in a landfill rather than a wet basin. By late
1986, selenium-laden wastewater no longer entered the lake (North
Carolina Department of Natural Resources and Community Development [NCDNRCD] 1986), and in subsequent years a stocking program
was successful in re-establishing adult populations of sport fish (eg,
centrarchids such as largemouth bass, Micropterus salmoides, and bluegill, Lepomis macrochirus). Follow-up studies were conducted in 1996 to
assess recovery of the ecosystem in Belews Lake (Lemly 1997). Tissue
selenium concentrations and associated impacts to fish were measured
and compared to pre-1986 conditions to determine how much change
had occurred since selenium inputs stopped. Findings were also examined using a hazard assessment protocol (see Chapter 4) to determine
if ecosystem-level hazards to fish and aquatic birds had changed as
well.
Results showed that waterborne selenium fell from a peak of 20 J.1g
SelL before 1986, to less than 1 J.1g SelL in 1996; concentrations in
biota were 85 to 95% lower in 1996. Hazard ratings indicated that high
hazard existed prior to 1986, and moderate hazard was still present in
1996, primarily due to selenium in the sediment-detrital food pathway. Concentrations of selenium in sediments fell by 65 to 75% during the period but remained sufficiently elevated (1-4 J.1g Se/g) to
contaminate benthic food organisms of fish and aquatic birds. Field
evidence confirmed the validity of the hazard ratings. Developmental
abnormalities in young fish persisted in 1996, indicating that selenium-induced teratogenesis and reproductive impairment were still
occurring a decade after selenium inputs stopped. Moreover, the residuallevels of selenium were sufficient to cause seasonal mortality in
young bluegill and other centrarchids because of Winter Stress Syndrome (see next section in this chapter), further impeding the recovery of fish populations. The latent effects occurred because of selenium
present in sediments, which was mobilized gradually, yet continually,
through the detrital food chain and accumulated to toxic levels in fish
tissues. Impacts to reproduction and overwinter survival of young fish
persisted, even though adult populations were re-established through
a stocking program. Projections indicate that several more decades may
be necessary for the Belews Lake ecosystem to fully recover (Lemly
1997). The low inflow of water and long retention time (volume replacement time about 1500 days), combined with low productivity (oligotrophic), tend to reduce natural flushing and enhance recycling of
selenium within the reservoir.