Task Force publishes second of four reports developing science-based testing strategy for maternal thyroid disruption

Brussels, 9 June 2021 – The second in a series of four reports on developing a science-based testing strategy for maternal thyroid disruption has just been published in the peer-reviewed medical journal Critical Reviews in Toxicology.

The report, by the Centre for chemical safety assessment (ECETOC) Special Thyroxine (T4) Task Force, looks at how different chemicals may cause harmful effects on the thyroid gland via different processes (known as “modes-of-action” or “adverse outcome pathways”).

In its report, “Towards a science-based testing strategy to identify maternal thyroid hormone imbalance and neurodevelopmental effects in the progeny – part II: how can key events of relevant adverse outcome pathways be addressed in toxicological assessments?”, the Task Force aimed to establish whether tests carried out on rodents enable the identification of thyroid-related modes-action potentially leading to adverse neurodevelopmental outcomes. It also studied the relevance of these effects on humans – in line with the European Commission’s Endocrine Disruptor Criteria.

EU guidelines on how to identify substances that can interfere with endocrine (hormone) systems are not clear on how toxicological testing can measure maternal thyroid hormone imbalance caused by chemicals. Nor are they clear on how to assess the potential for harmful consequences to child brain development.

To address these uncertainties, the Task Force collected data on important (molecular and cellular) events of modes-of-action and/or adverse outcome pathways that relate to the thyroid gland function being disrupted, both in humans and rodents. In addition, it assessed how parameters reflecting these events could be included in the planned scientific testing strategy.

Olivier De Matos, ECETOC Secretary General, said: “The review showed significant differences between humans and rodents in all processes related to thyroid function, but the biological implications of these differences are often still unknown. The Task Force has therefore identified further research needed to facilitate the development of the planned scientific testing strategy.”

He continued: “The T4 Task Force’s work is a great example of how ECETOC shapes scientific knowledge around the safety of chemicals, and then uses this to develop solutions to today’s scientific challenges.”

The Task Force’s first report, the ‘Human Evidence Paper’, completed at the end of last year, outlined the parameters from human studies that are most relevant for toxicological assessments. The  third and  fourth papers are currently under work by the Task Force and expected to be released the second half of 2021.