Research and analysis

Methodology for the scientific derivation of environmental assessment levels: summary

Published 21 March 2025

Applies to England

1. Chief Scientist’s Group report summary

This project updates the Environment Agency’s method for the scientific derivation of environmental assessment levels for air (EALs). It provides clarifications from the experience gained following the publication of new and revised EALs in recent years and illustrates its application with worked examples.

1.1 Background

Many industrial and waste management activities that could pollute the environment need a permit from the Environment Agency.  As part of the application process, operators may be required to complete an air-emissions risk assessment. This includes a comparison of predicted chemical emissions to air with relevant environmental standards.  Statutory environmental standards for air exist only for a small number of substances. The Environment Agency derives and publishes non-statutory standards for other substances commonly emitted by industrial processes.  EALs are the levels of a substance in air below which there is no appreciable risk or a minimal risk to public health.  EALs allow the Environment Agency to put the right level of protection in place for sites that we regulate.    

1.2 Approach

EALs are derived from toxicological risk assessment, which is based on the adverse effects of a substance on humans, evaluated or estimated based on the available knowledge.  This knowledge may include evidence of toxic effects from passive observation of human or animal exposure to the substance, but the main source is from more structured active investigation.  Where possible, human data from epidemiology (mainly occupational studies) or volunteer experimental studies is used. However, due to the ethical issues of human testing, many risk assessments rely on reported effects on laboratory animals.

Toxicological risk assessment is commonly described in four steps: hazard identification, hazard characterisation, exposure assessment, and risk characterisation.  The derivation of EALs primarily requires the use of the first two steps and these are outlined in the methodology document.

This project reviewed our existing guidance from 2012, updating it with more examples and useful clarifications taken from the development of new and revised EALs between 2020 and 2024.  The main updates included an expansion of the potential sources of information, new flow charts for EALs, and examples of the uncertainty factors used such as for the extrapolation from experimental exposure duration to long-term human exposure duration.  

1.3 Conclusions

This report sets out the Environment Agency approach to the derivation of EALs, which can be followed by industry and other organisations, although it is not a comprehensive how-to guide. Gathering, synthesising, and interpreting evidence on the human and mammalian toxicology of a substance is often a complex and challenging procedure. It should only be carried out by suitably qualified assessors with relevant experience, notably in toxicology. 

The Environment Agency will keep this methodology under review. Further experience on derivation of EALs for a range of substances and the continual development of new methods for toxicological assessment (many focusing on reducing the need for laboratory animal testing) will be considered.

1.4 Publication details

This summary relates to information from the following project:

• Title: Methodology for the scientific derivation of environmental assessment levels
• Project manager: Ian Martin, Chief Scientist’s Group

This project was delivered 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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