Medaka ( Oryzias latipes ) Multigeneration Test with Triclosan

The medaka extended one‐generation reproduction test (MEOGRT) is a tier‐2 study in the US Environmental Protection Agency's Endocrine Disruptor Screening Program and a level‐5 study in the Organisation for Economic Co‐operation and Development's conceptual framework. Integrating nonspecific apical and endocrine‐specific mechanistic endpoints, results of a MEOGRT can be used, with other data, in a weight‐of‐evidence evaluation to establish a dose–response relationship for risk assessment and identify potential causal relationships between an endocrine mode of action and adverse effects. The MEOGRT test design was used to evaluate the multigenerational effects of the antimicrobial agent triclosan. Japanese medaka were exposed to nominal concentrations of 1.4, 2.8, 5.6, 11, and 23 μg/L triclosan and a dilution water control starting with adult medaka (F0) through hatch in the second generation (F2). No consistent or concentration‐related responses occurred in the 182‐d test that suggested an endocrine‐mediated effect. There were no impacts on hepatic vitellogenin, secondary sex characteristics, or sex ratio that were linked to an adverse reproductive outcome. Histopathological responses were consistent with a toxic or stress effect, particularly when considered in context with observed reductions in growth. The overall population‐relevant no‐observed‐effect concentration was 11 µg/L based on effects on growth. The results of the present study support a previously conducted weight‐of‐evidence evaluation concluding that triclosan does not act as an agonist or antagonist within estrogen, androgen, thyroid, or steroidogenic pathways. Environ Toxicol Chem 2019;38:1770–1783. © 2019 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals, Inc. on behalf of SETAC.