Gunnison Basin Selenium Task Force

WHAT IS SELENIUM?

Selenium is an essential trace element that occurs naturally in the environment. Selenium is widely distributed in rocks, soils, water and living organisms. In the western United States, it is most common in marine sedimentary deposits like the local Mancos shale. Selenium is highly mobile and biologically available in arid regions having alkaline soils, typical of western Colorado's irrigated valleys.

WHY IS SELENIUM A PROBLEM?

The problem is:

Elevated levels of selenium have been shown to cause reproductive failure
and deformities in fish and aquatic birds.

Based on known margins of safety between normal and toxic dietary exposures, selenium is more poisonous than either arsenic or mercury. However, selenium, in minor amounts, is an essential trace nutrient for animals and humans. In July 1997, the State Water Quality Control Commission adopted a 5 ppb (parts per billion - see definition below) aquatic life standard for selenium in the Gunnison River Basin.

Several stream segments (see map)within the Gunnison basin did not meet this new standard, and the E.P.A then imposed temporary standards modifications to allow measures to be taken locally in an attempt to bring these segments into compliance.

Locally, it has been shown that deep percolation from irrigation, large quantities of groundwater movement, and other sources may increase selenium concentrations in streams, ponds, reservoirs, lakes and wetland areas. Upstream from the major irrigated areas in the Colorado River Basin, including the Gunnison and Uncompahgre River Basins, selenium concentrations are generally less than 1 ppb, but downstream from irrigated areas, the selenium concentrations in surface waters often exceed 5 ppb, the state standard.

The Gunnison Basin Selenium Task Force was formed to address these problems and resolve them at the local level.

What is a part per billion (ppb)?

It was not until just recently that advanced analytical techniques allowed scientists to detect trace elements, such as selenium, at the parts per billion level. Although as a toxic element, selenium can cause environmental problems even at very low levels, the following is provided to help us gain perspective on the quantities in question.

One part per billion compares with:

1 micro gram per liter (m g/L)

1 inch in 16,000 miles

1 second in 32 years

1 cent in $10 million dollars

1 pinch of salt in 10 tons of potato chips

1 bad apple in 2 million barrels.