Selenium in a Wyoming grassland community receiving wastewater from an in situ uranium mine

Water, soil, vegetation, grasshoppers, bird eggs, and bird livers collected at a 23.5-ha (58 acres) grassland irrigated with wastewater from an in situ uranium mine (study area) and a reference site in 1998 were analyzed for selenium and other trace elements. Selenium concentrations in the uranium mine wastewater applied onto the grassland ranged from 340 to 450 microg/L. Selenium in the upper 15 cm (6 in) of soil from the irrigated grassland at the mine ranged from 2.6 to 4.2 microg/g dry weight (DW). Mean selenium concentrations in soil and water were 5 and 15 times higher at the study area than at the reference site. Selenium concentrations in grasses and grasshoppers ranged from 6.8 to 24 microg/g and 11 to 20 microg/g DW, respectively. Selenium in red-winged blackbird eggs and livers collected from the study area ranged from 13.2 to 22 microg/g and 33 to 53 microg/g DW, respectively, and concentrations were well in excess of toxic thresholds. Mean selenium concentrations in grasses, grasshoppers, and bird eggs and livers were 5.8 to 30 times higher at the study area than at the reference site. Elevated selenium concentrations in water, soil, grasshoppers, and red-winged blackbird eggs and livers collected from the study area demonstrate that selenium is being mobilized and is bioaccumulating in the food chain.