OECD | Draft Detailed Review Paper on the inclusion of thyroid endpoints in OECD fish tests

This document presents a detailed review paper (DRP) on the thyroid hormone system (THS) in fish and identification of potential THS related endpoints for inclusion in existing OECD fish test guidelines, prepared by Denmark.

There is increasing concern that many chemical compounds may act as thyroid hormone (TH) disrupters. However, there is a clear lack of THS related endpoints in OECD fish test guidelines. In this DRP, the THS of fish is described, possible THS related endpoints proposed in the scientific literature are identified and their usability as endpoints in OECD fish test guidelines is assessed. The objective is to identify endpoints applicable for assessment of THS disrupting chemicals in fish. Numerous measurable molecular, histological and morphological endpoints in fish are dependent on the THS and many different THS disruption pathways with various molecular initiating events are identified. The DRP does not present an exhaustive evaluation of all available studies for all endpoints (e.g. gene expression). However, the DRP provides a summary of the literature up to 2021 including all key studies considered relevant to making assessments of the various endpoints. In general, studies using the chemicals most widely accepted as THS disrupting compounds, e.g. perchlorate, propylthiouracil, methimazole, iopanoic acid, and halogenated flame retardants, are included.