The history and development of FETAX (ASTM standard guide, E-1439 on conducting the frog embryo teratogenesis Assay-Xenopus)

The energy crisis of the 1970's and 1980's prompted the search for alternative sources of fuel. With development of alternate sources of energy, concerns for biological resources potentially adversely impacted by these alternative technologies also heightened. For example, few biological tests were available at the time to study toxic effects of effluents on surface waters likely to serve as receiving streams for energy-production facilities; hence, we began to use Xenopus laevis embryos as test organisms to examine potential toxic effects associated with these effluents upon entering aquatic systems. As studies focused on potential adverse effects on aquatic systems continued, a test procedure was developed that led to the initial standardization of FETAX. Other .than a limited number of aquatic toxicity tests that used fathead minnows and cold-water fishes such as rainbow trout, X. laevis represented the only other aquatic vertebrate test system readily available to evaluate complex effluents. With numerous laboratories collaborating, the test with X. laevis was refined, improved, and developed as ASTM E-1439, Standard Guide for the Conducting Frog Embryo Teratogenesis Assay-Xenopus (FETAX). Collabrative work in the 1990s yielded procedural enhancements, for example, development of standard test solutions and exposure methods to handle volatile organics and hydrophobic compounds. As part of the ASTM process, a collaborative interlaboratory study was performed to determine the repeatability and reliability of FETAX. Parallel to these efforts, methods were also developed to test sediments and soils, and in situ test methods were developed to address "lab-to-field extrapolation errors" that could influence the method's use in ecological risk assessments. Additionally, a metabolic activation system composed of rat liver microsomes was developed which made FETAX more relevant to mammalian studies.