Chemical risk assessment has long relied on a robust and pragmatic premise: assess a substance, characterise its hazards, estimate exposure and derive safe levels for defined uses. This logic remains essential. It underpins European frameworks for industrial chemicals, pesticides, biocides, food and feed, cosmetics, pharmaceuticals, consumer products and occupational exposure. Yet real-world exposure is rarely organised by regulatory sector. Humans, animals and ecosystems may encounter multiple substances from food, packaging, personal-care products, medicines, workplaces, indoor environments and the wider environment. The challenge is not that single-substance assessment has become obsolete, but that it now needs to be connected more systematically with combined-exposure thinking.
That distinction matters. The EU’s One Substance, One Assessment (OSOA) framework, which entered into force in January 2026, is designed to improve coherence, transparency and efficiency across chemical assessments. OSOA improves coherence across single-substance assessments, while mixture toxicity highlights the need to connect these assessments across exposure contexts. In other words, mixture toxicity is not a competing agenda. It is part of the same movement towards better integrated chemical governance.
This policy direction is increasingly reflected in the scientific debate. A recent article in Science argued that EU chemical risk management should better account for coincidental mixtures through concepts such as a Mixture Allocation Factor, using the “risk cup” metaphor to show how individually acceptable exposures can still contribute to an overall cumulative burden. The point is not that every substance requires the same level of concern, but that risk management needs ways to recognise when several small contributions may jointly occupy the available safety space.
Building on this policy direction, mixture toxicity is no longer only a scientific concern but is becoming an operational priority in Europe. The Partnership for the Assessment of Risks from Chemicals (PARC) is developing tools, case studies and regulatory options for improved assessment and management of chemical risks, including co-exposure to multiple chemicals and mixture risk assessment. This places mixture toxicity within a broader European agenda: safer chemicals, improved evidence generation, reduced animal testing, and more usable data for risk assessors and risk managers.
Regulatory science has already made concrete progress. EFSA has developed methodologies for cumulative risk assessment, particularly for pesticides grouped by common toxicological effects, and the RIVM Monte Carlo Risk Assessment (MCRA) platform continues to support probabilistic cumulative exposure and risk assessment. The European Commission’s Chemicals Strategy for Sustainability also explicitly recognises that combined exposure to multiple chemicals must be addressed more effectively and ECHA is a key implementation actor in this landscape, particularly through its role in data, regulatory processes and new approach methodologies. Taken together, these initiatives show that mixture assessment is not being built from scratch, but is being progressively embedded into existing European regulatory infrastructure.
The practical difficulty is deciding which mixtures should be assessed. The number of possible combinations is effectively unlimited. Regulators therefore need prioritisation strategies based on co-exposure patterns, shared endpoints, common mechanisms of action, vulnerable populations, or substances that contribute most to an overall risk burden. This prioritisation step is essential because mixture assessment cannot be reduced to testing every possible combination. It requires a structured way to identify where combined exposure is most plausible, most relevant and most likely to affect the margin of safety. This is where the science becomes highly data-dependent. Without structured information on occurrence, exposure, toxicological endpoints, mode of action and uncertainty, even well-established mixture models become difficult to apply consistently.
Interactions between chemicals add another layer of complexity. Additivity is often used as a pragmatic and protective default, but synergistic or antagonistic effects may occur in specific biological contexts. Classic work on endocrine-active substances showed that mixtures can produce relevant effects even when individual components are present at levels that appear low when assessed alone. Such examples remain important, but they should be interpreted carefully: the regulatory question is not whether every mixture is synergistic, but how to identify the combinations, endpoints and exposure windows that deserve deeper assessment.
The methodological toolbox is also changing rapidly. High-throughput screening, omics technologies, adverse outcome pathways, quantitative structure-activity relationships (QSAR), read-across, toxicokinetic modelling and probabilistic approaches are increasingly relevant to mixture assessment. The direction of travel is reinforced by recent EU developments. In June 2026, the European Commission published its roadmap towards phasing out animal testing for chemical safety assessments, and ECHA convened the first meeting of its Collaborative Platform on Alternatives to Animal Testing . These initiatives are expected to increase the need for transparent, structured and mechanistically interpretable evidence.
This is where data integration becomes central. It is not an accessory issue. It is the infrastructure that makes mixture thinking possible. Exposure data, toxicological reference values, mechanistic evidence, monitoring results, literature evidence and regulatory decisions must be findable, interoperable and reusable across domains. The planned EU common data platform on chemicals under OSOA, EFSA’s OpenFoodTox 3.0 migration into IUCLID and OECD Harmonised Templates, and the JRC’s IPCHEM platform all point in this direction. The remaining challenge is not only to collect more data, but to connect data in forms that support assessment, prioritisation and uncertainty analysis.
The cross-sector dimension is particularly important. Mixture toxicity is relevant to pesticide residues and environmental contaminants, but also to food additives, feed additives, cosmetics, pharmaceuticals, biocides, consumer products, industrial chemicals and substances encountered in occupational settings. The same individual or ecosystem may be exposed through several routes and regulatory domains. This reinforces the need for approaches that do not collapse sector-specific expertise, but make it easier to connect evidence across sectors. A food-chain assessor, a REACH assessor, a cosmetics expert and an occupational-risk specialist may each hold part of the evidence needed to understand the same real-world exposure picture. The value lies in making those pieces interoperable without losing their regulatory context. In this context, organisations working at the interface of data, toxicology and regulatory science have a practical role to play. Innovamol supports evidence mapping, structured toxicological data and computational workflows. Through a combination of internal tools and scientific-regulatory expertise, it helps organise heterogeneous evidence, identify data gaps, connect hazard and exposure information, and make uncertainty explicit for human experts. Addressing mixture toxicity is therefore not only about adding complexity to risk assessment. It is about making chemical safety assessment more realistic, more transparent and more usable for decision-making.
“The whole is more than the sum of its parts” – Aristotle