US Fish & Wildlife Service


Date of this Version



Published in Contaminant Report Number: R6/712C/97, 1-33, (1997)


Bird mortalities have been documented in oilfield waste pits in Wyoming and various other oil-producing states in the western United States. In the semi-arid West, migratory birds mistake wastewater ponds or pits for wetlands. Most refineries use large ponds to contain their wastewater. One refinery in Casper, Wyoming actively discharged refinery wastewater into a closed basin, Soda Lake. This created a wetland that attracts numerous aquatic birds, in particular, nesting colonies of gulls (Larus spp.), terns (Sterna spp.), double-crested cormorants (Phalacrocorax auritus), eared grebes (Podiceps nigricollis), dabbler ducks (Anas spp.) and American avocets (Recurvirostra americana). Soda Lake is a popular site with local birdwatchers. Wastewater was discharged into a small pond (Pond 1) adjacent to Soda Lake (Pond 2). Water from Pond 1 flowed through a spillway into Pond 2. The refinery ceased discharging wastewater in 1990. The objectives of this study were to determine if trace element and hydrocarbon concentrations in sediment and biota from Soda Lake are present in concentrations adverse to migratory aquatic birds. Selenium was elevated in aquatic invertebrates, bird livers and bird eggs but not in sediment or pondweed (Potomageton vaginatus). Selenium concentrations were above threshold levels known to cause impaired reproduction and embryonic deformities in aquatic birds (Lemly 1993). Sediments collected near the inlet of Pond 1 contained elevated concentrations of chromium, copper, mercury and zinc. Sediments collected near the water inlet at Pond 1 had almost equal proportions of odd- and even-numbered aliphatics suggesting recent or chronic exposure to petroleum compounds. Carbon Preference Index (CPI) values for sediments from Pond 1 ranged from 0.58 to 1.1. CPI values less than 3 indicate oiled sediments (Farrington and Tripp 1977). Sediment samples from the inlet at Pond 1 also had high concentrations of oil and grease. Additionally, a visible sheen was observed on the water's surface after the sediments were agitated during collection. Odd-numbered aliphatics and pristane were greater than even-numbered aliphatics and phytane in pondweed and aquatic invertebrates. This indicates hydrocarbons of a biogenic origin. Hydrocarbons in gadwall livers collected from Pond 1 were probably petrogenic as indicated by approximately equal proportions of odd- and even-numbered aliphatics, high ratios of pristane and phytane to n-C17 and n-C18, respectively, and CPI values less than 3. Additionally, metabolized PAH's were detected in gadwall bile also suggesting exposure to petroleum hydrocarbons. Pond 1 had higher PAH concentrations in sediment and biota than did Pond 2.