Research and analysis

Characterising the hazard of highly persistent substances that exhibit low levels of bioaccumulation: summary

Published 3 February 2022

Applies to England

1. Chief Scientist’s Group report summary

This project found a standard exposure model can identify highly persistent chemicals for which a more conservative regulatory assessment may be appropriate. This work is important for determining and prioritising the potential hazard and risk management of these chemicals.

1.1 Background

Chemicals that are highly persistent but do not accumulate in living organisms can remain in water for a long time. Concerns are growing internationally that current regulatory processes may not adequately control risks. They have the potential to travel to areas far from the point of release, where they may eventually reach concentrations that could result in adverse environmental effects.

1.2 Approach

We explored the environmental assessment of this type of chemical by modelling two case study per- and polyfluorinated alkyl substances (PFAS), PFHxA and GEN-X, which are known to be very persistent. We wanted to determine whether a standard exposure model is suitable, investigate alternative modelling approaches and consider whether a hazard-based assessment may be more appropriate than the current risk-based approach.

1.3 Results

We found that the current quantitative approach to risk assessment at a local and regional scale appears to be equally appropriate for highly persistent substances as for non-persistent substances. An approximate “time to steady-state” can also be calculated at the global scale from our standard regulatory model outputs, and this could be a useful metric for decision-making. For the water environment, the concentration at the local scale is typically the highest environmental concentration modelled, and therefore a worst case for the purposes of risk assessment.

1.4 Next steps

Uncertainties remain with the use of a quantitative risk assessment approach due to the length of time the chemicals remain in the environment. These could be addressed by requiring a more conservative assessment or using a hazard-based approach.

A way forward for the regulatory hazard and risk assessment of highly persistent substances may be to make a distinction, based on modelling results, between those substances that are predicted to reach steady-state within a few years and those that are predicted to reach steady-state over much longer periods. Substances with longer times to steady-state may build up in remote regions at a global scale, and the concentrations in such regions would be expected to decline very slowly following a cessation or reduction in emission.

1.5 Publication details

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

• Title: Characterising the hazard of highly persistent substances that exhibit low levels of bioaccumulation
• Project manager: Claire Massey, Chemicals Assessment Unit, Chief Scientist’s Group
• Research Contractor: Peter Fisk Associates

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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