Is the Fish Embryo Acute Toxicity Test Under Threat?
The SETAC Global Animal Alternatives Advisory Group propose that the FET test is considered more favorably than the ECHA-sponsored report may seem to suggest it ought to be.
After nearly eight years of formal development, a previous decade of investigational science and the most rigorous validation exercise for any new ecotoxicity test guideline to demonstrate reliability, robustness and repeatability, the Organization for Economic Co-operation and Development (OECD) fish embryo acute toxicity (FET) test guideline was officially adopted in 2013.
The test had already been previously adopted in Germany for assessing the acute toxicity of wastewater effluents in place of an acute fish toxicity assay to avoid unnecessary use of fish. However, for the assessment of wastewater purposes, the duration of the test was only 48 hours.
During the development of the FET test, it was recognized that some chemicals (e.g., cationic polymers) may not elicit their toxic potential until the embryo is free from the protective outer shell (chorion), and for this reason the OECD FET test was extended to 96 hours to encompass hatching. As a result, the 96 hour FET test was now able to comparably predict the acute toxicity of these chemicals.
One potential drawback with the FET test, which was established before the OECD test guideline was accepted, was its insensitivity to certain neurotoxicants requiring metabolic activation to cause toxicity to occur. But this is now well recognized, and with the addition of co-factors to the test solutions, comparable FET toxicity data to that in juvenile fish has been observed. Equally, interspecies differences between fish acute toxicity data for substances that require metabolic activation to elicit a toxic response is also a recognized phenomenon with some organophosphate substances differing by a factor of >100 between fish species. On the other hand, certain other chemicals causing developmental effects during embryogenesis (when approximately 90% of the genome is active) are not as acutely toxic to juvenile fish compared with the FET test.