ENSR Consulting & Engineering. 4413 W. LaPorte Avenue. Ft. Collins, Colorado 80521. Figure 1. Framework for ecological risk assessment (Modified.
APPLICATION OF ECOLOGICAL RISK ASSESSMENT PRINCIPLES TO NATURAL RESOURCES DAMAGE ASSESSMENT Alan W. Maki Exxon Company, USA 600 Jefferson, Suite 900 Houston, Texas 77002 Ernest Brannon University of Idaho 3370 Blain Road Moscow, Idaho 83843
Walter D. Pearson Battelle 439 West Sequim Bay Road Sequim, Washington 98382
Jerry M. Neff Battelle Ocean Sciences 397 Washington Street Duxbury, Massachusetts 02332
William A. Stubblefield ENSR Consulting & Engineering 4413 W. LaPorte Avenue Ft. Collins, Colorado 80521
ABSTRACT: Ecological risk assessment principles are basic to the assessment of environmental injury during the Natural Resources Damage Assessment (NRDA) process; however, what is sought is quantified injury, rather than quantified risk, to valued ecosystem components. These principles were used to develop an NRDA program for studies of injury to herring and pink salmon populations in Prince William Sound (PWS), Alaska, following the Exxon Valdez oil spill. Overall, exposures and subsequent effects of the spill on herring and salmon were minimal and post-spill harvests of the year’s classes that were at greatest risk of spill injury were at or near record levels.
An ecological risk assessment includes an exposure assessment and a biological effects assessment (Cairns et al., 1978; EPA, 1992). Estimates of the concentrations of the chemicals of concern to the environment are converted to estimates of the chemical doses while, concurrently, the effects assessment measures the impacts of the estimated exposure in terms of biological effects on valued ecosystem components (Figure 1).
Characterization of exposure To characterize hydrocarbon exposure, the most extensive post-spill water quality monitoring programs ever conducted were completed in spill-path areas of PWS (Wells et al., 1995). Resulting data indicate that exposures of pelagic fish, such as herring and salmon, averaged below 1 ppb, well below known acute and chronic effect levels. Fortunately, less than 10% of herring spawning activity in 1989 and 1990 occurred along oiled shorelines. Additional samples of salmon spawning stream sediments also confirmed that exposure of incubating eggs and alevins was low (Wells et al., 1995). Therefore, results of the exposure assessment phase indicate that both species had low potential for exposure to toxicologically significant concentrations of hydrocarbons from the oil spill. However, full examination of potential for injury must also include an assess-
Figure 1. Framework for ecological risk assessment (Modified from USEPA, 1992.)
1025
1026
1997 INTERNATIONAL OIL SPILL CONFERENCE Table 1. Summary of field and laboratory studies completed to assess effects of the Exxon Valdez oil spill on herring and pink salmon
Characterization of effects Characterization of exposure Measures of hydrocarbons: • In water column • In sediments • Along shorelines • In herring eggs • In fish tissues
Herring
Pink salmon
Spawning activity Egg development and hatching Larval growth and development Larval mortalities
Embryo survival Alevin growth and survival Early marine growth Adult spawning
Figure 2. Harvest and run-size data for Prince William Sound herring and pink salmon
ment of biological effects on the subject species as discussed in text following.
Characterization of ecological effects Pacific herring. Several field and laboratory studies were conducted to examine the effects of the spill on key life stages of herring (Table 1). The 1989 and 1990 biological results were consistent with the low exposure of herring, and there is no evidence of injury at the population level. Pink salmon. Similarly, several field and laboratory studies were completed to examine injury to the pink salmon population (Wells et al., 1995). These studies looked at key salmon life stages from 1989 to 1995 and indicate that the spill did not cause biologically significant harm to the PWS pink salmon population (Table 1). Also, post-spill harvests of both species for the year’s classes at greatest risk were at or near record levels (Figure 2).
Conclusions The strength of the ecological risk assessment paradigm lies in its ability to establish supportive relationships between exposures to crude
oil in various environmental media (dose) and biological effects reported for valued species (response), and thus properly identify spillrelated injury. Adherence to the risk assessment paradigm allowed measurements of subtle effects on key life stages of herring and pink salmon. Reported effects were highly localized in time and space, and therefore had no net impact on the PWS populations of either species.
Biography Alan W. Maki is currently Environmental Advisor at Exxon Company, USA, Houston, Texas.
References 1. Cairns, J. Jr., K. L. Dickson, and A. W. Maki, eds., 1978. Estimating the hazard of chemical substances to aquatic life. ASTM STP 657, American Society for Testing and Materials, Philadelphia, 278pp 2. U.S. Environmental Protection Agency, 1992. Framework for ecological risk assessment. EPA/630/R-92/001, Washington, D.C. 3. Wells, P. G., J. N. Butler and J. S. Hughes, eds., 1995. Exxon Valdez oil spill: Fate and effects in Alaskan waters. ASTM STP 1219, American Society for Testing and Materials, Philadelphia, 965pp
