There is currently heightened concern about the impact of chemicals on ecosystems and human health, with industrial chemicals, pesticides and pharmaceuticals all in the spotlight. The EU’s Chemicals Strategy for Sustainability aims for a pollution-free environment by 2050.
With this in mind, chemical risk management at the European level is being reviewed, although no major changes to the EU’s Regulation on the Registration, Evaluation, Authorization and Restriction of chemicals (REACH) are expected in the near future. Nevertheless, this process keeps open the possibility of future amendments and offers an opportunity to improve the way the EU regulates chemical-related harms, including by addressing the underrepresented topic of chemical mixtures which a team of chemists has drawn attention to in a recent policy paper published in Science.
Decision-makers currently look at individual substances and intentional mixtures of chemicals, but the researchers argue that it is difficult to assess the safety of new chemicals coming to market without considering coincidental mixtures which occur when new chemicals are introduced into an environment where other chemicals are already present. They suggest the introduction of a ‘mixture allocation factor’, or MAF, to address this gap.
To embed the MAF into REACH regulation, they offer the ‘risk cup’ concept, which was originally conceived by the US Environmental Protection Agency to evaluate cumulative pesticide risks. This idea demonstrates that even when individual chemicals fall within safe limits within their individual ‘cups’, when combined in a single cup they can exceed the cup’s capacity, becoming unsafe at those levels of exposure. To bring the mixture back within safe boundaries, stricter limits for the chemicals posing the largest risk should be imposed.
The mixture allocation factor would function as a correction factor when assessing the safety of each chemical in isolation. For example, in a mixture of five chemicals, the maximum MAF value is 5, so each could occupy 1/5 of the risk cup. In this scenario, any chemicals with a MAF of more than 1 would be seen as high-risk, having caused the risk cup to ‘overflow’ and resulted in unacceptable levels of chemical risk. As such, only higher-risk chemicals (those with the largest MAF numbers) would be affected by mixture related regulation, while manufacturers of lower-risk chemicals would be left unburdened with risk management.
The researchers suggest that such an approach could initially be implemented for industrial chemicals and broadened in the future to include the likes of pesticides and pharmaceuticals.
The team also acknowledged that the key regulatory issue for introducing the mixture allocation factor would be choosing specific MAF values, (i.e. the size of the ‘risk cup’) with a need to balance protection of humans and ecosystems without making unnecessary alterations to risk assessments, particularly for chemicals that contribute negligibly to mixture risks. Initially, a modest MAF size could be used to introduce ‘mixture awareness’ into chemical risk management. This could then be reviewed and if necessary revised as new data emerge.
The proposal is backed by empirical arguments. The team suggest it is wrong to assume that mixtures of individual chemicals with different modes of action, within regulatory thresholds, cannot cause combined effects. They note that threshold levels of chemicals rarely carry no residual risk, and that different chemicals seldom act in isolation; instead, their modes of action combine in unintended ways. Sticking with the present logic goes against fundamental biological principles on the interactive nature of cells, tissues and organs, they argue, citing a study on chemical mixtures and sperm quality that shows cumulative chemical exposure exceeded acceptable total limits by factors of 5 to 100 in that research context alone.
Not every mixture poses unacceptable risks, and some chemicals contribute very little to overall combined risk, argue the researchers. However, to effectively protect humans and the environment we must move away from the assumption that chemicals can be dealt with as discrete entities.
REACH legislation is still under discussion and as such, while this study presents no new primary data, it offers a concrete, timely proposal that informs policymakers of the benefits of considering the risks posed by chemical mixtures. Thttps://environment.ec.europa.eu/news/new-rules-streamlining-chemical-assessments-enter-force-2026-01-05_enhe researchers suggest that their proposed approach is pragmatic and could be easily incorporated into REACH through the risk cup concept, avoiding detailed mixture risk calculations for each of the thousands of available chemicals.
Reference:
S Backhaus, T., Scholze, M., Brack, W., Martin, O., Slunge, D., Ågerstrand, M., Kortenkamp, A. and Escher, B., 2025. Include a mixture allocation factor to improve EU chemical risk management. Science, 390(6774), pp.678-680.
To cite this article/service:
“Science for Environment Policy”: European Commission DG Environment News Alert Service, edited by the Science Communication Unit, The University of the West of England, Bristol.
Notes on content:
The contents and views included in Science for Environment Policy are based on independent, peer reviewed research and do not necessarily reflect the position of the European Commission. Please note that this article is a summary of only one study. Other studies may come to other conclusions.
