Selenium in the Gros Ventre Watershed

Selenium is a semi-metalic element that is essential for both human and animal health. However, a narrow range exists between the essential amount and toxic levels. Elemental selenium is commonly found in soils containing Cretaceous and Tertiary marine rock. The Gros Ventre River Watershed is located in an area containing six geologic formations associated with selenium: Cody, Frontier, Frontier, Morrison, Phosporia, and Steele. Water filtering through seleniferous geologic formations and soil can oxidize elemental selenium into a soluble form, selenate (SeO42-), which readily bio-accumulates up the food-chain. Local biologists have noted nest failures and poor productivity in bald eagles, trumpeter swans, and ospreys in this watershed.

The objective of the study is to determine how much selenium is bio-accumulating through the food chain in the Gros Ventre Watershed by sampling species from varying trophic levels (i.e., algae, aquatic snails, fish, ravens, ducks, eagles, swans).

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Many plants in the species of Astragalus, Machaeranthera, Haplopappus, Stanleya, Atriplex, Castilleja, Grindelia, and Gutierrezia are selenium indicators and selenium accumulators. This soluble from of selenium is of concern because it can bio-accumulate in aquatic and terrestrial food chains. Ingestion is the main uptake pathway for bio-accumulation. Cases of cattle poisoning due to ingestion of seleniferous vegetation have been documented in Wyoming. Common symptoms seen in these animals were shedding of hooves, hair loss, partial blindness, restriction of swallowing, inability to stand, blind staggers, and even death (Beath, 1982). Ducks, eagles, trumpeter swans, and ravens can also experience selenium poisoning. Excess selenium can interfere with reproduction, causing embryo deformities and even abortion of embryos. Selenium concentrations as low as 0.8-2.1mg/L have been determined to be toxic to waterfowl and birds of prey (Peterson and Nebeker, 1992).