Contributions of radioecology to the development of some modern concepts of ecotoxicology : From ecological half-life to monitored natural attenuation

Savannah River Ecology Laboratory, P.O. Drawer E, Aiken, South Carolina 29803, U.S.A.

Abstract

Many of the modern concepts used in ecotoxicology have historical roots in earlier thinking from the field of radioecology. An example is the concept of Monitored Natural Attenuation (MNA), which is an approach to the remediation of contaminated waste sites, based on the natural degradation, sequestration or aging of toxic substances ; contaminant inventory reduction proceeds in the absence of engineered treatment or removal activities. Because of potentially reduced costs compared to other alternatives for waste site remediation, MNA has rapidly become a popular topic for research and development. Many years ago however, the field of radioecology recognized that biota and other ecosystem components contaminated with radioactive materials naturally decreased their contaminant burdens over time as the result of physical isotope decay and/or as the contaminants were sequestered or otherwise became unavailable for biological uptake. In the field of radioecology, this process is quantified as the ecological half-life (EHL), which is the time required for a population or other ecosystem component to reduce its contaminant burden by 50 % after first coming into a steady-state with contaminant levels in other parts of its environment. Because of the ease with which they can be quantified in living organisms and environmental media, gamma-emitting radionuclides have proved particularly useful for describing and quantifying EHLs in a variety of habitats. We summarize EHL studies based on more than 30 years of data for declines in ¹³⁷Cs levels in habitats at a former nuclear weapons production facility in the southeastern United States. These studies of EHL are then related to the development of MNA programs for non-radioactive contaminants in these same or similar habitats. Of particular importance is the finding that EHL's can vary between habitat types for the same contaminant. Even within the same habitat, EHL's can vary spatially across microhabitats as well as between ecosystem components (e.g. in plants vs. animals) or even between species within a single trophic level/taxonomic group.