37    ASSESSING ECOLOGICAL HAZARD TO
AMPHIBIAN POPULATIONS
Douglas J. Fort, Vice President
Enos L. Stover, President
The Stover Group
Stillwater, Oklahoma 74076
INTRODUCTION
Worldwide declines in amphibian populations have recently attracted much attention by the
scientific, and particularly the environmental risk assessing community. Many theories have been
postulated to explain these declines, including changes in habitat, decreased fitness, UV light
stress, and most commonly, anthropogenic contamination of the environment. Although scientists have been studying the population dynamics of amphibian populations for years, acknowledging the world-wide declines and decreased fitness of this class of organisms, it has been only
recently that evaluation of potential hazards to amphibian species has been incorporated into
ecological risk assessment. Lack of consideration of amphibian species was not due to a devaluing of the importance of amphibians, but primarily because no bioassays had been developed,
standardized, and validated to monitor the potential hazards to amphibian species. Thus, the lack
of amphibian-based monitoring tools warranted the development of useful model systems for
evaluating potential ecological hazards to amphibian populations. Frog Embryo Teratogenesis
Assay-Xenopus (FETAX) which was developed in 1983 by Dumont and co-workers,1 but only
recently validated and standardized by the American Society for Testing and Materials
(ASTM),2-25 has proven useful in cost-effectively evaluating hazards both in the workplace and
in the environment. FETAX has been used to screen pure chemical products, surface waters,
groundwaters, effluents, sediments, and soils in support of ecological risk assessment. In this report, we describe the FETAX assay and the utility and versatility of this assay in ecological hazard assessment.
HISTORY OF AMPHIBIAN-BASED TOXICITY TESTS
The first recorded test of environmental samples with amphibian species in a somewhat "controlled setting" was in the late 1960s and early 1970s. None of the testing was performed with
standardized bioassays, but each study paved the way for the development of the FETAX model.
Amphibian embryos and larvae have been exposed to a variety of toxic chemicals. Herbicides,26
fungicides,21 insecticides,28 metals,29-30 and many other chemicals and mixtures have been tested
in a variety of amphibian species.3'-36 The results of this early work convinced researchers that
amphibian embryos were sensitive early indicators of water quality. However, factors such as
species used, exposure time, water dilution, and temperature varied greatly from study to study,
making comparison of the results nearly impossible. Several groups, including the laboratories of
Birge,37-38 Dial,39 and Greenhouse,40-42 were instrumental in comparing the sensitivities of different anuran species under differing environmental conditions and beginning the long process of
standardization. The development of the FETAX model followed shortly, although validation of
the model is still being completed at the present time, particularly for biomedical applications
and human health hazard evaluation.
THE TEST ORGANISM, Xenopus laevis
As with any bioassay system, the selection of the appropriate test organism is imperative if the
model system is to be successful. Different test organisms will change the specificity, sensitivity.
51st Purdue Industrial Waste Conference Proceedings, 1996. Ann Arbor Press, Inc., Chelsea, Michigan 48118.
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