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Determining Significant Endpoints for Ecological Risk Analysis

T. G. Hinton, J. D. Congdon, C. Rowe, David Scott 
 (Savannah River Ecology Laboratory)
and J. Bedford, F. W. Whicker
(Colorado State University)

Background

The Department of Energy (DOE) is faced with complex decisions regarding the clean-up of contaminated sites. Ecological risk analyses can contribute greatly to the decision-making process. The science of quantifying risk to humans from exposure to radiation is well developed and internationally accepted. In contrast, the methods, endpoints and interpretation of ecological risk analyses are still being developed and lack standardization (see Table 1). Our goal is to provide DOE with a scientifically defensible protocol for measuring ecological risks. A sound protocol is possible only when sub-lethal cellular damage (i.e., from exposure to chronic, low-level radiation or chemical contaminants) is related to the performance of individuals and the persistence of populations.

Table 1. Fundamental Differences In Human and Ecological Risk Analyses

Research Objectives

We plan to establish protocols for assessing ecological risks by coupling measured molecular damage to effects observed at the individual and population levels of biological organization. Our working hypothesis is that molecular damage leads to changes in metabolic rate due to the increased cost of maintenance and repair. Changes in energy allocation potentially will affect: growth rates, age at maturity, fecundity, age-specific survivorship, and longevity.

At present this research focuses primarily on:
1) developing a molecular probe to quantify cellular damage due to exposure to low-level radiation;
2) quantifying individual- and population-level responses of organisms exposed to contaminants; and
3) constructing an experimental facility (Guarded Experimental Tank Facility for Understanding Contaminant Transfer) to examine effects of chronic low-level radiation and heavy metal exposure on aquatic organisms in mesocosms.

Metabolic Rate as an Indicator of Stress from Contaminant Exposure

Metabolic rate measures an animal's cost of maintenance or activity. Changes in metabolic rates have implications for processes such as energy storage, growth and reproduction. The metabolic rate of exposed organisms may be an excellent physiological measure of sub-lethal stress because it reflects multiple processes occurring within an organism. Metabolic rate may therefore be used to determine whether cellular effects from contaminant exposure are of significance at higher levels of biological organization. We have documented increased metabolic rates in numerous species of animals exposed to non-radioactive contaminants from a coal ash basin (D-Area basin on the SRS). To see representative results, click on the link below:

Representative Results

Currently we are testing:
whether metabolic rates increase in animals exposed to chronic, low-level radiation;
how changes in metabolic rates differ when organisms are exposed to both radioactive and non-radioactive contaminants; and
how previous exposures to contaminants affect the metabolic response from subsequent exposures.

(For more information on this aspect of our work, contact: Dr. Justin Congdon; 803 -725-2472; congdon@srel.edu)

The Irradiation-Mesocosm Facility

We plan to rear animals in 50 outdoor mesocosms designed to test effects of chronic, low-level irradiation, alone and in conjunction with metal contaminants. Replicate treatments and powerful statistical methods are possible. Each "radiation" mesocosm will have a sealed 137-Cs source located above it. Radiation exposures to animals will be varied by varying the strength of the source, and quantified by using thermoluminescent dosimeters.

For more images relating to the mesocosm, click here.

By using a variety of organisms we can determine:
the frequency of chromosome damage at various radiation exposures and metal contaminant concentrations;
the relationship between cellular damage and metabolic rate; and
treatment effects on an individual's energy allocation pattern, growth and survival.

Benefits to the DOE are:
reduce uncertainties associated with ecological risk analyses;
provide defensible scientific evidence on which cleanup decisions can be based; and
broad application across DOE sites reduce DOE's need to take an ultra-conservative approach to cleanup, resulting in substantial cost savings.

(Funded by an EMSP grant from the DOE)
For more information contact : Dr. Tom Hinton, 803 -557 -7454; thinton@srel.edu

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