Dick Halbrook, Glenn Suter and Bradley Sample, scientists in ORNL's Environmental Sciences Division, have found no apparent difference in the reproductive success of great blue heron or osprey who eat moderately contaminated fish and birds of the same species who feed on uncontaminated fish. However, in a related experiment they found that a mammal species, the mink, had fewer young after eating fish from contaminated streams (fish make up one-half of the mink's diet).
The great blue heron is a long-necked, fish-eating wading bird with a long tapering bill, large wings, and soft plumage. The osprey is a large fish-eating hawk. The mink is a semiaquatic carnivorous mammal that resembles a weasel and has partially webbed feet, a short bushy tail, and a soft thick coat.
Fish in nearby Poplar Creek and the Clinch River, where the ORNL study was conducted, are contaminated with polychlorinated biphenyls (PCBs), mercury, and other heavy metals. PCB mercury levels in fish from the Clinch River and Poplar Creek are less than that seen in fish from locations in Lake Michigan. Contaminants in fish from the Great Lakes are suspected to have adverse effects on populations of fishing-eating wildlife.
Halbrook reports that the eggs and chicks of the heron were found to contain PCBs and mercury, but their levels were less than what is known to adversely affect other bird species. All heron chicks observed in this study were born normal and showed no defects. The number of offspring of the mink was lower than usual, but the young were normal.
For this study of ecological risk at a DOE site, Sample applied a pioneering ecological risk assessment method that Suter and Larry Barnthouse (formerly of ORNL) developed in the 1980s for the U.S. Environmental Protection Agency (EPA). EPA is currently using this method to assess the risk to the health of plants and animals of different types and levels of environmental contaminants.
The method considers several lines of evidence regarding the results and effects of contamination. Examples are the concentrations of each contaminant in the tissues of fish and of the birds eating it, damage to DNA in living cells and other bioindicators, reproductive success of birds and mammals exposed to contaminants, and the numbers and types of fish present.
Studies like the Oak Ridge investigation help test the validity of ecological risk assessment methods and models for predicting contaminant effects on plants, animals, and entire ecosystems. Such experimental results and field data allow risk assessors to correct their methods and models so more accurate predictions can be made.
This project was conducted as part of the Comprehensive Environmental Response, Compensation, and Liability Act (CERCLA) remedial investigation of the Clinch River and Poplar Creek and is being funded by the Department of Energy's Environmental Restoration Program. A primary objective of the remedial investigation was to determine whether contaminants pose a sufficient risk to human health or the environment to justify or necessitate cleanup actions.
ORNL, one of the Department of Energy's multiprogram research laboratories, is managed by Lockheed Martin Energy Systems, which also manages the K-25 Site and the Y-12 Plant on the DOE Oak Ridge Reservation and the environmental management activities at the Paducah, Ky., and the Portsmouth, Ohio, gaseous diffusion plants.