Brussels, 09 February 2020 – An article by the Centre for chemical safety assessment (ECETOC) Special Thyroxine (T4) Task Force has recently been published in the peer-reviewed medical journal Critical Reviews in Toxicology.
The scientific and regulatory communities are concerned about a potential connection between low thyroid hormone levels in the blood of pregnant mothers, in particular thyroxine, and impaired mental development in their children.
The 2018 European Food Safety Authority/European Chemicals Agency Guidance on identifying endocrine disruptors is unclear about how the presence (or absence) of substance-induced maternal thyroid hormone imbalance, or its potential for harmful consequences in child neurodevelopment, should be established by toxicological testing. This has caused uncertainty for companies producing plant protection products, or biocides, as well as within the regulatory community.
Shortly after the above-mentioned guidance publication, ECETOC established a ‘Special T4 Task Force’ with the aim of tackling the uncertainties. The Task Force is reviewing the evidence that can be used to develop a science-based tiered testing strategy to identify, first, if a substance has the ability to disrupt thyroid hormones in mothers and potentially cause neurodevelopmental effects in their children; and second, if effects observed in tests on rodents are relevant for humans.
The new report, ‘ Toward a science-based testing strategy to identify maternal thyroid hormone imbalance and neurodevelopmental effects in the progeny – Part I: Which parameters from human studies are most relevant for toxicological assessments?’, is the first in a series of four reviews and outlines which parameters from human studies are most relevant for toxicological assessments. It goes on to identify additional research that is needed to contribute to the development of toxicity testing strategies.
Overall, the data support the conclusion that low maternal thyroid hormone levels can lead to an increased risk of impaired brain development in children. It was not possible to identify the most sensitive parameter(s) to assess effects in pregnant mothers or children, or specific hormone levels indicating increased risks (both of which would need to be reflected in the planned testing strategy).
The second review in the series, ‘Towards a science-based testing strategy to identify maternal thyroid hormone imbalances and neurodevelopmental effects in the progeny – Part II: How can key events of relevant adverse outcome pathways be addressed in toxicological assessments?’ has also been submitted to Critical Reviews in Toxicology. The report looks at adverse neurodevelopmental outcomes in mammals. It aims to establish if standard rodent toxicity test methods and in vitro assays allow identifying thyroid-related modes-action potentially leading to adverse neurodevelopmental outcomes, and the human relevance of effects – in line with the European Commission’s Endocrine Disruptor Criteria.
The third and potentially the fourth papers are currently under work by the Task Force and expected to be released the second half of 2021.
Olivier De Matos, ECETOC Secretary General, said: “The Special T4 Task Force is a great example of our Science Programme’s core mission at work: enhancing the effectiveness and efficiency of chemicals safety assessment using the very best scientific knowledge and techniques available.”