Recommendations

Recommendation 1

Given the risk of harm due to the lack of current regulation and high uncertainty stemming from systemic data gaps, Defra and the Environment Agency should look to rapidly implement pragmatic and precautionary regulation for chemical mixtures in aquatic environments. As new evidence, data and methodologies become available and uncertainty decreases, the regulation should evolve towards a probabilistic and risk-based approach for different chemicals and/or chemical classes.

At present, chemical safety assessments in the UK are largely conducted on a single-chemical basis. Yet as this report has described, there is a weight of evidence – considering experimental, observational and mechanistic data – that suggests that even when chemicals are present individually, at potentially ‘safe’ concentrations, mixtures of environmental chemicals can have adverse effects on aquatic ecosystems, above and beyond the sum of their constituent parts. Innovative approaches are expanding our ability to predict environmental co-exposure and its potentially harmful effects. However, significant uncertainties and data gaps are likely to persist into the future.

In view of these uncertainties, it is not yet feasible to implement a fully informed probabilistic, risk-based, regulatory system for chemical mixtures. Given this and the risk of harm, we recommend that a precautionary approach, enshrined in UK law under the Environment Act 2021 (Section 17), be pragmatically applied in the interim with respect to environmental chemical mixtures. This should be with the aim of reducing the number of chemicals in the environment in the immediate term, recognising the risk of harm posed by chemical mixtures, as well as moving towards a more risk-based and probabilistic approach to mixture regulation as the evidence, data and tools become available. There are many ways this could be achieved (examples in Box 1) and options should be explored in detail along with a review of the current approach to individual chemical regulation and/ or new legislation, risk-management and regulation specific to diffuse mixture effects.

Recommendation 2

To capitalise on opportunities for faster, more accurate and cost-effective risk assessment, Defra and relevant UK agencies should become early adopters of innovative approaches for monitoring, managing and regulating chemical mixtures in the aquatic environment.

Innovative scientific approaches such as ‘new approach methodologies’ (NAMs), machine learning and ‘omics’ techniques, present potentially transformative opportunities for managing and regulating chemical mixtures in the environment. Given these opportunities and the possible cost-saving benefits, UK regulators and agencies (eg the Environment Agency, the Scottish Environmental Protection Agency and the Health and Safety Executive) should look to become early adopters of these approaches and work closely with researchers to operationalise these techniques for use in policymaking. For example, the Hazardous Substances Advisory Committee has recently published a paper outlining how NAM’s could be adopted into UK chemical regulation (footnote 1). Over time, the adoption of new methods may allow a shift towards the development of probabilistic risk assessments for mixtures, leading to an estimate of the likelihood of harm, while accounting for uncertainties in data.

However, it is important to recognise that new approaches are unlikely to address the significant data gaps and biases in our current knowledge base in the short term. Many environmental chemicals remain poorly studied and our understanding of their effects varies across chemical classes, exposure scenarios and endpoints. This uneven distribution highlights the need for a dual strategy: embracing new techniques while simultaneously prioritising research efforts to fill critical knowledge gaps (see Recommendation 4).

Recommendation 3

Address the fragmentation of current chemical monitoring data by creating a centralised, open-access hub. This might be achieved using the National Data Library that is currently being developed by the Department for Science, Innovation and Technology.

Current datasets related to chemical pollutants are stored in different repositories and some of these data are poorly curated and never published in open access databases. This makes it difficult to use these data for risk assessment without committing time and resources to obtaining the data and readying them for use, creating an immediate barrier for researchers, regulators and policymakers seeking to integrate datasets to understand chemical mixture risk. Establishing a data ‘hub’ would greatly aid mixture risk research and regulation and would minimise duplication of scientific effort.

Those establishing the data hub should consider mechanisms for encouraging industry participation via data sharing, while protecting commercial interests. The hub should be accompanied by guidance and reporting templates to support the use of these data for regulatory purposes – from collection and experimental procedures to the reporting of results. The ‘National Data Library’ of public sector data, announced in the 2024 Labour manifesto (footnote 2) and currently being developed by the Department for Science, Innovation and Technology, may be an appropriate means of delivering this.

Recommendation 4

UKRI should coordinate the development of an interdisciplinary research strategy that incentivises collaboration between funders, researchers, industry stakeholders and regulators, targeting critical evidence gaps with respect to the effects of chemicals and their mixtures.

Research into the effects of chemical mixtures does not currently target key evidence gaps, meaning significant uncertainty remains regarding the effects of mixtures in the environment. For example, published mixture studies are biased towards already relatively well-researched chemicals and species and few studies go beyond binary or tertiary mixtures (2 – 3 chemicals) (footnote 3). Targeted research efforts could usefully focus on lesser-studied chemicals and validation of findings in real-world environments.

Researchers, funders, industry stakeholders and regulators should collaborate to develop an interdisciplinary research strategy to guide research efforts and funding to target key evidence gaps. This strategy should clearly delineate between fundamental research that will likely require state investment and ‘near market’ research that could be industry funded. Given novel chemicals will continue to be developed, this agenda-setting process must be iterative to adapt to new challenges and ensure that the latest research continually informs policy and regulation. In the short term, retrospective research that integrates diverse datasets might be an effective means of establishing strong correlations between mixtures and their impacts.

Recommendation 5

To address current skills and expertise gaps, regulatory agencies such as the Environment Agency and Cefas should prioritise the development of a future pipeline of appropriately trained toxicologists and ecotoxicologists.

The UK needs to invest in toxicology and ecotoxicology expertise. Firstly, it is critical that the current workforce is supported to remain at the forefront of scientific innovation through continuous professional development. For example, to capitalise on the opportunities presented by machine learning or NAMs, regulators, contract research organisations and industry will need to develop skills and expertise so that they know how and when these techniques may be beneficially used and how to interpret and critically appraise the results.

Secondly, the UK currently faces a concerning decline in skilled applicants for toxicology and ecotoxicology roles and a limited number of specialised academic programmes (footnote 4). These challenges are particularly acute given the increased regulatory burden following the UK’s exit from the EU. Training programmes should equip emerging toxicologists and ecotoxicologists with a holistic skill set, including an understanding of the fast-moving science and familiarity with regulatory frameworks, to bridge the divide between scientific research and regulatory processes. In England, the Environment Agency and Cefas should work together as regulatory agencies to invest in and develop the pipeline of expertise required to deal with toxicology-related regulatory challenges.

Box 1: Example policy options for implementing a pragmatic approach to chemical mixture risk

Illustrative and hypothetical examples of policy options that could be used to regulate chemical mixtures. These interventions aim to reduce the number of chemicals in the environment in the immediate term and achieve more risk-based and probabilistic approaches to chemical mixture regulation in the future. The options are indicative only and exclude direct financial controls such as taxes and levies, as well as behaviour-based interventions such as codes of conduct changes, supply chain scrutiny, labelling and advertisement.

Detect and monitor to allow preventative action

Investing in the detection and monitoring of chemicals/chemical mixtures and their effects in aquatic environments could, if coupled with a dynamic regulatory response mechanism, allow regulators to take much swifter action when these are found to be present and causing harm. Persistent and bioaccumulative chemicals (like PFAS) could then be identified, phased out and/or tightly controlled before widespread contamination occurs. Techniques such as environmental DNA and biomarkers (see Chapter three), combined with analysis using machine learning, can be used to regularly monitor the environment and more quickly identify concerning exposure-effect relationships.

Adapt the regulation and/or management of individual chemical contaminants

Minimising the number of contaminants entering the environment is the most effective way to reduce the exposure risk from mixture effects. There are several ways this could be achieved, some examples include:

• Moving towards a more circular economy for chemicals, aiming to reduce, reuse and recycle (advances in green chemistry have a lot to offer in this regard (footnote 5));
• Tighter regulations to restrict or ban chemicals (especially persistent chemicals), based on potential hazards, not just proven harm;
• Target the existing risk assessment process, for example, by implementing a Mixture Assessment Factor (MAF) (footnote 6). Applying a MAF lowers the acceptable concentration of a substance being discharged, providing a greater chemical ‘safe space’ to allow for mixture effects.

Group contaminants based on shared properties for risk assessment

This approach aims to group contaminants based on shared properties such as structures, modes of action or adverse effects – and these groupings could be used to assess and regulate mixture risk (New Approach Methodologies can be particularly helping for informing these groupings, see Chapter three). Grouping can be done in either a precautionary or more targeted way, depending on the amount of information available. An approach such as this could increase efficiency and help to prevent “regrettable substitution” (replacing one hazardous chemical with another similar one). Particularly problematic groups of persistent or rapid/acutely damaging chemicals could also be more heavily regulated on this basis. Regulators could choose to consider shared properties or mechanisms of action at relevant geographic scales, for example water catchment areas.

Reduce the amount of known contaminant mixtures entering the environment

Additional risk assessments could be performed for groups of chemicals that are known to enter the environment as chemical mixtures. For example, mixtures of chemicals emitted from single industrial, manufacturing or formulation sites. This approach could reduce exposure to known contaminant mixture risk before those mixtures become widespread in the environment. This is similar to how co-formulants are considered in pesticides legislation (footnote 7).

Implement regulation based on the level of risk associated with exposure

This could target particularly vulnerable or important species or habitats and aim to minimise or remove the number of chemicals entering these environments. Such an approach would likely have to be catchment-based, recognising the interconnectedness of freshwater, estuarine and marine systems and consider vulnerable species from a more diverse range of phyla than are currently tested.

Restrict chemicals shown to be harmful, either individually or as components of mixtures to only ‘essential’ uses and if no safer alternatives exist

This could require an agreed definition of what an ‘essential use’ and ‘safer alternative’ is – but is an example of a pragmatic approach, where some degree of use is tolerated if the benefits are seen to outweigh the risks.