Research and analysis

Deriving acceptable concentrations for endocrine disrupting chemicals using aquatic toxicity data: summary

Published 29 January 2026

1. Chief Scientist’s Group report summary

There is no current regulatory guidance on determining acceptable concentrations for environmental endocrine disrupting chemicals (EDCs) under the UK Registration, Evaluation, Authorisation and restriction of CHemicals (UK REACH) regulation. This project aimed to close this gap by testing approaches to derive predicted no effect concentrations (PNECs) using aquatic ecotoxicity datasets, and ensuring these thresholds are protective of mechanistic effects. This is relevant to both the risk assessment and risk management of EDCs, including applications for authorisation under UK REACH.

1.1 Background

Several “Substances of Very High Concern” are listed in Annex 14 of UK REACH based on their endocrine disruption potential in wildlife. Their continued use requires authorisation by demonstrating either “adequate control” or “socioeconomic need”.

Applications for the authorisation of EDCs have only been based on socioeconomic need to date, as there is no guidance on how an “adequate control” argument can be made. This project reviewed available ecotoxicology data to assess how a PNEC could be set that represents a suitable threshold for this purpose. PNECs are extrapolated from ecotoxicity test data using assessment factors which reflect how comprehensive the dataset is, to account for uncertainties.

1.2 Methodology

The project reviewed available environmental endocrine disruption data for three well-characterised EDCs to derive PNECs for the aquatic environment. We found that suitable PNECs could be derived by applying assessment factors to the lowest no-observed effect concentration from reliable and relevant studies. The size of the assessment factor depends on the position of the data in the Organisation for Economic Co-operation and Development’s conceptual framework (OECD CF) for the testing and assessment of endocrine disruptors. This framework describes five study levels, each giving a different amount of confidence in the results based on study duration and life stage(s) covered as well as the parameters measured. We tested the concept by applying our initial findings to eight further EDCs with smaller amounts of data. The approach covers EDCs acting via oestrogen, androgen, and steroidogenesis modes of action, but not ones affecting the thyroid due to limited data.

1.3 Results

The project found that the multi-generation fish tests at OECD CF Level 5 provide sufficient data to allow a PNEC to be derived using an assessment factor of 10. The less comprehensive studies at Level 4 also provide sufficient data but require a larger assessment factor of 100. If only Level 3 screening data are available, an indicative PNEC can be derived using a very large assessment factor of 1000.

1.4 Conclusions

The report shows that it is possible to derive precautionary threshold values for EDCs from aquatic toxicity test data. It also shows that a varying assessment factor based on the level and quality of the data can generate pragmatic endocrine disrupting PNECs that are protective of mechanistic endocrine effects. This is relevant to both the risk assessment and risk management of EDCs, including applications for authorisation under UK REACH.

1.5 Publication details

This summary relates to information from the following project:

• Title: Deriving acceptable concentrations for endocrine disrupting chemicals using aquatic toxicity data
• Project managers: Ian Doyle and Morné Van Der Mescht, Chemicals Assessment Unit
• Research Contractor: wca Environment Limited

This project was commissioned by the Environment Agency’s Chief Scientist’s Group, which provides scientific knowledge, tools and techniques to enable us to protect and manage the environment as effectively as possible.

Enquiries: research@environment-agency.gov.uk.

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