Trace Elements and Petroleum Hydrocarbons in the Aquatic Bird Food Chain Of Process Water Evaporation Ponds at the Little America Refinery, Casper, Wyoming

This study determined the nature and extent of trace elements, metals, and petroleum hydrocarbons in evaporation ponds used for the disposal of process water from Sinclair Oil Corporation’s LARCO oil refinery in Evansville, Wyoming. This study was conducted to determine if contaminants are causing adverse effects or have the potential to adversely affect aquatic migratory birds inhabiting the evaporation ponds. The discharge of refinery process water into relict dune basins created a series of ponds that provide habitat for 39 species of aquatic migratory birds. Several aquatic bird species nest at the evaporation ponds and the adjacent natural marsh complex. Migrating waterfowl and shorebirds also use the ponds as a stop-over with peak numbers (between 1,000 and 2,000 birds) occurring in mid-September during the fall migration. The refinery evaporation ponds are highly eutrophic and contain elevated concentrations of arsenic, chromium, copper, mercury, nickel, lead, selenium, and zinc in bottom sediments. Sediments from the nearby Russian Olive Pond contained elevated concentrations of arsenic, chromium, mercury and nickel. Polycyclic aromatic hydrocarbons (PAHs) were also present in high concentrations in sediments from the three evaporation ponds. Although these trace elements and PAHs are elevated in the bottom sediments, eutrophication is likely limiting the availability of these contaminants to the food chain and aquatic migratory birds. Some trace elements such as selenium are accumulating in the food chain and PAHs are present in algae and aquatic invertebrates. Selenium bioaccumulation was documented in aquatic birds nesting at the ponds. Selenium concentrations in black-necked stilt eggs (mean = 13.6 μg/g) exceeded the 6 to 7 μg/g threshold associated with impaired egg hatchability in black-necked stilts. Selenium concentrations in livers from prefledged juvenile American avocets (mean = 13.8 μg/g) and blue-winged teal (mean = 20.1 μg/g) exceeded background for avian livers of 10 μg/g level. Other species of waterfowl, such as widgeon, gadwall, and Northern shoveler, feeding on algae and aquatic invertebrates in the evaporation ponds are probably also bioaccumulating selenium at levels of concern. PAH bile metabolites and analysis of the liver detoxification enzyme ethoxyresorufin-O-dealkylase (EROD) shows that aquatic birds feeding in the evaporation ponds are exposed to petroleum hydrocarbons; however, it is not known if this exposure is resulting in adverse effects. The eutrophic nature of these ponds is precluding the establishment of macrophytic aquatic vegetation as well as limiting the density and diversity of aquatic invertebrates, both dietary items consumed by aquatic migratory birds. Eutrophication and its contribution of organic matter onto the surficial sediments is likely limiting the bioavailability of trace elements and petroleum hydrocarbons as these contaminants are strongly bound to the organic matter within the sediment. Although eutrophication is limiting the availability of chemical contaminants in the food chain, the potential exists for the presence of cyanotoxins produced by cyanobacteria in the evaporation ponds