5.1 FETAX is a rapid test for identifying potential developmental toxicity. Data may be extrapolated to other species including mammals. FETAX might be used to prioritize samples for further tests which use mammals. Validation studies using compounds with known mammalian or human developmental toxicity, or both, suggest that the predictive accuracy will exceed 85 % (2) . When evaluating a test material for mammalian developmental toxicity, FETAX must be used with and without a metabolic activation system (MAS). Use of this exogenous MAS should increase the predictive accuracy of the assay to approximately 95 %. The accuracy rate compares favorably with other currently available “ in vitro teratogenesis screening assays” (3). Any assay employing cells, parts of embryos, or whole embryos other than in vivo mammalian embryos is considered to be an in vitro assay.

5.2 It is important to measure developmental toxicity because embryo mortality, malformation, and growth inhibition can often occur at concentrations far less than those required to affect adult organisms.

5.3 Because of the sensitivity of embryonic and early life stages, FETAX provides information that might be useful in estimating the chronic toxicity of a test material to aquatic organisms.

5.4 Results from FETAX might be useful when deriving water quality criteria for aquatic organisms (4).

5.5 FETAX results might be useful for studying structure-activity relationships between test materials and for studying bioavailability.

1.1 This guide covers procedures for obtaining laboratory data concerning the developmental toxicity of a test material. The test utilizes embryos of the African clawed frog, Xenopus laevis and is called FETAX (Frog Embryo Teratogenesis Assay-Xenopus) (1).² Some of these procedures will be useful for conducting developmental toxicity tests with other species of frogs although numerous modifications might be necessary. A list of alternative anurans is presented in Appendix X1.

1.2 A renewal exposure regimen and the collection of the required mortality, malformation, and growth-inhibition data are described. Special needs or circumstances might require different types of exposure and data concerning other effects. Some of these modifications are listed in Appendix X2 although other modifications might also be necessary. Whenever these procedures are altered or other species used, the results of tests might not be comparable between modified and unmodified procedures. Any test that is conducted using modified procedures should be reported as having deviated from the guide.

1.3 These procedures are applicable to all chemicals either individually or in formulations, commercial products or mixtures that can be measured accurately at the necessary concentrations in water. With appropriate modification these procedures can be used to conduct tests on the effects of temperature, dissolved oxygen, pH, physical agents, and on materials such as aqueous effluents (see Guide E1192), surface and ground waters, leachates, aqueous and solid phase extracts, and solid phase samples, such as soils and sediments, particulate matter, sediment, and whole bulk soils and sediment.

1.4 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.

1.5 This guide is arranged as follows:

Section

Referenced Documents

2

Terminology

3

Summary of Guide

4

Significance and Use

5

Safety Precautions

6

Apparatus

7

Water for Culturing Xenopus adults

8

 Requirements

8.1

 Source

8.2

 Treatment

8.3

 Characterization

8.4

FETAX Solution Water

9

 Requirements

9.1

 Formulation

9.2

Test Material

10

 General

10.1

 Stock Solution

10.2

Test Organisms

11

 Species

11.1

 Source

11.2

 Adults

11.3

 Breeding

11.4

 Embryos

11.5

Procedure

12

 Experimental Design

12.1

 Temperature and pH Requirements

12.2

 Beginning the Test

12.3

 Renewal

12.4

 Duration of Test

12.5

 Exogenous Metabolic Activation System (MAS)

12.6

 Biological Data

12.7

Analytical Methodology

13

Acceptability of the Test

14

Documentation

15

Keywords

16

Appendixes

17

 X1. List of Alternative Species

Appendix X1

 X2. Additional Endpoints and Alternative Exposures

Appendix X2

 X3. Concentration Steps for Range-Finding Tests

Appendix X3

 X4. Microsome Isolation Reagents and NADPH Generating
   System Components,

Appendix X4

References