Date of this Version
The objectives of this study were to compare refinery-related petroleum hydrocarbon concentrations in nestling tree swallows (Tachycineta bicolor) and nestling house wrens (Troglodytes aedon) at sites along the North Platte River Casper, Wyoming in 1997 and 1998; and to determine if contaminants were present in concentrations that could adversely affect the birds. Because trace element concentrations, mixed function oxidase activity, and the variation in DNA are often associated with petroleum hydrocarbon concentrations in birds, each was measured as indicators of petroleum contamination. Sediment and aquatic invertebrates were also sampled for characterizing a possible contaminant source to the birds. Sampling areas included sites upstream (Game & Fish, Patterson-Zonta Park), adjacent to (Amoco Park, Texaco Refinery), and downstream (EKW State Park) of the former Amoco and Texaco oil refineries. We also sampled one site between the Amoco and Texaco Refineries (Crossroads Park). Additional samples were taken using adult cliff swallows (Hirundo pyrrhonota) nesting under various bridges along the North Platte River in 1998.
Several aliphatic hydrocarbons were detected in sediment, aquatic invertebrates, and carcasses and gastrointestinal contents of house wren and tree swallow nestlings and adult barn and cliff swallows from all sites but differences among sites were not significant. The low pristane to n-C17 ratio in avian diet and tissues did not suggest chronic or acute exposure of birds to petroleum at any of the locations. However, the high phytane to n-C18 ratios of the gastrointestinal contents may indicate that some of the dietary items consumed by the birds were recently or chronically exposed to petroleum products.
Most polycyclic aromatic hydrocarbons (PAHs) were not detected in aquatic insect larvae but some were detected in sediments. Concentrations of total PAHs were detected in nestling carcasses of tree swallows, house wrens, and a bank swallow. Differences in PAH concentrations were not significant among sites for tree swallow nestlings but were for house wren nestlings. In gastrointestinal contents of both tree swallow and house wren nestlings, PAH concentrations tended to be higher at the Texaco Refinery site when compared to the Game & Fish site. Two hepatic monooxygenase activities, benzyloxyresorufin-O-dealkylase (BROD) and ethoxyresorufin-Odealkylase (EROD), in tree swallow livers also tended to be higher at the Texaco Refinery site than at the Game & Fish sites and their induction may be related to PAH exposure. Because of the small sample size, results of the flow cytometry analysis, which measured DNA content, were inconclusive. Adult cliff swallow carcasses showed significant differences in total PAHs among sites with the highest concentrations occurring at the Texaco Refinery site and the upstream Patterson-Zonta Park site. PAHs were not detected in gastrointestinal contents of the cliff swallows. The predominance of unsubstituted PAHs and the general lack of alkyl-PAHs in all samples suggests that most of the PAHs were combustion-derived.
Most trace elements were not elevated in any of the samples. Chromium and selenium were elevated in aquatic insect larvae but differences among sites were not significant. Chromium was not detected in avian eggs or most nestling livers but was detected in nestling tree swallow and wren carcasses and one adult barn swallow carcass. Mercury was detected in one bank swallow egg and all tree swallow eggs. Mercury was significantly higher in tree swallow eggs collected at the EKW State Park site when compared to the Game & Fish site. Mercury was detected in wren eggs from EKW State Park but was not detected in eggs from the Game & Fish site or in two of the three eggs from the Texaco Refinery site. In tree swallow and wren nestling livers from EKW State Park and the Texaco Refinery site, mercury concentrations were significantly higher than from the Game & Fish site. Mercury was also detected in tree swallow nestling carcasses from both the Texaco Refinery and EKW State Park but not from the Game & Fish site or in any of the house wrens. Differences were not significant among sites and the source of the mercury is unknown. Concentrations of mercury were detected in adult barn and cliff swallow livers and carcasses. Selenium was detected in house wren and tree swallow eggs, livers, and nestling carcasses. Selenium was also detected in adult barn and cliff swallow livers and carcasses. Differences were not significant but selenium concentrations, probably the result of irrigation return flows, tended to decrease downstream.
This study demonstrates that some refinery-related contaminants are bioavailable and birds are being exposed. However, the data do not exhibit any pattern that can be linked to the refineries. Our small sample size and limited statistical power do not allow us to determine if any of the contaminants are adversely affecting the birds; and, the data collected on adult birds are inconclusive because exposure to contaminants may have occurred outside the sampling area. Additionally, for several contaminants detected, the upstream Game & Fish site appears to have concentrations similar to the study sites. Finally, we were unable to determine the influence of yearly variation on the results of the petroleum hydrocarbon or trace element analyses from 1997 and 1998; but, the 1997 data from the EKW State Park were not critical to the overall conclusions of the manuscript.