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<br />Hypothesis of Historical Effects from Selenium
<br />
<br />1990). They exceeded the 85th percentile in samples collected in 1972 to 1973
<br />(2.9 J.l,g/g dw, assumes 73% moisture) in fish at five out of six Colorado River
<br />basin stations (Green River at Vernal, UT [only upper basin station] and
<br />Colorado River at Imperial Reservoir, Lake Havasu, Lake Mead, and Lake
<br />Powell, all in AZ). Selenium concentrations in whole-body fish also exceeded
<br />the 85th percentile in 1978 to 1981 (2.5 J.l,g/g dw, based on a mean 72%
<br />moisture in 591 samples) and 1984 (2.8 J.l,g/g, based on a mean 74% moisture
<br />in 315 samples) at six out of seven stations (same five) plus Colorado River at
<br />Yuma, AZ. Selenium concentrations in samples from only the station on the
<br />Gila River (San Carlos Reservoir, AZ) have not exceeded the 85th percentile.
<br />Several DOl National Irrigation Water Quality Program (NIWQP) studies
<br />in the Colorado River basin have reported elevated concentrations of sele-
<br />nium and other elements in water, sediment, and biota in aquatic environ-
<br />ments where endangered or threatened fish occurred historically, but are rare
<br />now. NIWQP studies of federal irrigation projects that have documented
<br />elevated selenium concentrations in the upper Colorado River basin include
<br />the Gunnison River basin, which included the Uncompahgre and Gunnison
<br />rivers and several tributaries and other water bodies (Butler et at., 1991, 1994,
<br />1996), the Grand Valley, which included the upper Colorado River and tribu-
<br />taries in the Grandjunction, CO, area (Butler, Osmundson, and McCall, 1989;
<br />Bulter et at., 1994, 1996), the Sanjuan River, Mancos River, McElmo Creek,
<br />and other water bodies in northwestern New Mexico and southwestern Colo-
<br />rado (Blanchard, Roy, and O'Brien, 1993; Butler et at., 1995; Thomas et at.,
<br />1997), and the middle Green River basin, along with Anderson Bottom, Ashley
<br />Creek, Desert Lake Waterfowl Management Area, Escalante Ranch, Pariette
<br />Wetland, Sheppard Bottom, Stewart Lake, and other water bodies in north-
<br />eastern Utah (Stephens, Waddell, and Miller, 1988; Stephens etaL, 1992; Peltz
<br />and Waddell, 1991).
<br />Other studies have documented elevated selenium concentrations in water
<br />and fish from the upper Colorado River basin, including the Yampa and Price
<br />rivers (Waddell and Wiens, 1993; Bussey, Kidd, and Potter, 1976; Stephens and
<br />Waddell, 1998). Peltz and Waddell (1991) and Stephens et at. (1992) are the
<br />only NIWQP reports to include information on selenium concentrations in
<br />endangered fish, which seemed elevated in several tissues. Butler et at. (1996)
<br />is the only report to include a risk assessment of potential adverse effects of
<br />selenium on endangered fish, which concluded there was a low to moderate
<br />hazard for adverse effects from waterborne selenium on three early life stages
<br />of endangered fish; the hazard from dietary exposure would probably be
<br />higher because of the bioaccumulative nature of selenium in the food chain.
<br />Based on information in the Green River studies, Modde (1993) stated that
<br />"Based on the distribution of razorback sucker, it is likely that a significant
<br />portion of the remaining razorback sucker population in the middle Green
<br />River have been exposed to selenium contamination." A similar concern was
<br />expressed by Stanford and Ward (1991) who stated "Relatively high [sele-
<br />nium] concentrations were observed in the larger fishes of Lake Powell (Potter
<br />
<br />Hum. Eco!' Risk Assess. Vol. 5, No.6, 1999
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