Research and analysis

Evaluation of the potential approaches to risk assessment of unintentional chemical mixtures for future UK REACH assessments: summary

Published 17 August 2022

1. Chief Scientist’s Group report summary

This joint report by the Environment Agency and the UK Health Security Agency identifies a recommended approach to address the risks to both the environment and human health from unintentional mixtures of chemicals under the UK Registration, Evaluation, Authorisation and restriction of Chemicals (REACH) Regulation. This work is important in informing future updates to UK REACH.

1.1 Background

There is international agreement that exposure to mixtures of chemicals has the potential to result in adverse effects in both people and the environment, even where individually the chemicals are below concentrations of concern. This can be the result of additive effects, for example. However, the current risk assessment approach under UK REACH considers chemicals in isolation as it applies to the manufacture and use of discrete registered substances. We therefore wanted to consider how the potential risk from unintentional mixtures (as may be formed following release of the registered substance into the environment) could be incorporated into the risk assessment approach for industrial chemicals.

1.2 Approach

We summarised the different methods available to estimate mixture risk and reviewed studies that have estimated potential mixture toxicity based on measured chemical concentrations. We considered the benefits and disadvantages of different methods that can be used to assess the risks from unintentional mixtures.

1.3 Results

We found that it is practically impossible to identify in advance which specific substances have the potential to contribute most to mixture risk, as this varies depending on the specific sites, time points and populations investigated. Due to this, the application of a Mixture Assessment Factor (MAF) in risk assessment calculations is a pragmatic way forward. A MAF is an additional “safety factor”, which can either be used to derive ‘acceptable’ thresholds based on (eco)toxicity data or applied to the risk characterisation ratio (where a predicted or measured exposure concentration is divided by the acceptable threshold concentration). Either way, it would make risk assessment more conservative as it adds an additional layer of precaution.

Alternative approaches to a MAF require further data and resource before they can be applied, and the use of a MAF would retain the principle that it is the responsibility of the UK REACH Registrant to demonstrate that risks are adequately controlled. For the environment, a MAF of 5 appears to be appropriate and protective for most surface waters. For human health, it is not considered appropriate to apply a MAF at this time.

1.4 Next steps

Our report focussed on the scientific considerations of how the potential risk from unintentional mixtures could be addressed under UK REACH. We will continue to provide advice to the Department of the Environment, Food and Rural Affairs and other government bodies whilst they consider whether changes should be made to the current risk assessment approach.

1.5 Publication details

This summary relates to information reported in detail in the following output:

• Title: Evaluation of the potential approaches to risk assessment of unintentional mixtures for future UK REACH assessments
• Project manager: Claire Massey, Chemicals Assessment Unit, Chief Scientist’s Group
• Research Contractor: Environment Agency and UK Health Security Agency

This project was published 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.

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