Toxicology of selenium in a freshwater reservoir: implications for environmental hazard evaluation and safety

A study was conducted to document patterns of accumulation and toxicity of selenium to organisms in a power plant cooling reservoir in North Carolina. Selenium entered the reservoir by way of effluent from the coal ash disposal basin, which contained 100-200 micrograms Se/liter. Concentrations of selenium in the lake water averaged 10 micrograms/liter, but were accumulated from 519 times (periphyton) to 3975 times (visceral tissue, largemouth bass) in the biota. The pattern and degree of accumulation was essentially complete within 2 years after the initial operation of the power plant, and persisted throughout the remainder of the study: fishes greater than insects greater than annelids greater than molluscs greater than crustaceans greater than plankton greater than periphyton. The plantonic and detrital food pathways exposed fishes to potential dietary concentrations of selenium that were some 770 and 519-1395 times the waterborne exposure, respectively. Of the 20 species of fish originally present in the reservoir, 16 were entirely eliminated, 2 were rendered sterile but persisted as adults, 1 was eliminated but managed to recolonize from a relatively uncontaminated headwater area as sterile adults, and 1 was unaffected. Two nonnative fish species were accidentally introduced and established reproducing populations. Abundance and diversity of biota other than fishes was not affected. Relative to control habitats, the contaminated reservoir had concentrations of waterborne selenium that were 20-30 times background levels; the flora and fauna contained about 10-15 times background. The results show that selenium can accumulate and be biologically magnified to toxic levels in a reservoir even though waterborne concentrations are in the low microgram per liter range. This study also provides data which indicate that current toxicological information is neither accurate when used to predict the relative sensitivity of individual fish species to selenium, nor is it sufficient to predict community responses in a natural setting. It is very likely that long-term elevation of waterborne selenium to 8-10 micrograms/liter in warm-water lakes and reservoirs would result in biotic responses similar to those documented in this report.