An exposure to a single, pure chemical does not exist in the real world. Instead, chemical pollution is characterised by complex multi-component mixtures that can easily comprise dozens or even hundreds of chemicals. How can we keep people and the environment safer from the potential harm caused by chemical mixtures? The European Commission has proposed the Mixture Assessment (or Allocation) Factor (MAF) as part of the Chemicals Strategy for Sustainability (CSS) to streamline mixture risk assessment, or in other words, to assess the safety of chemicals when they are combined together. However, the specifics of MAF implementation remain underdeveloped, limiting broader discussion on its regulatory application.

Different approaches to estimate Mixture Assessment Factor (MAF)

In response to the request to include the MAF in the upcoming REACH revision, PARC has intensively engaged in an activity led by the Austrian Agency for Health and Food Safety to scrutinize various MAF types and their estimation methods as outlined in scientific literature and by stakeholders. This effort aims to identify the most suitable MAF type for integration into chemical safety assessment under REACH and similar regulatory frameworks. Notably, the so-called “MAF_ceiling” approach has emerged as a straightforward option, notably not requiring additional (eco)toxicological data. The MAFceiling is a tool that works by lowering the maximum acceptable level of risk posed by a chemical, from a value of 1 to below 1. This adjustment is important because it considers the combined effect of multiple chemicals. Setting such a lower limit ensures that even if several chemicals co-occur, the total risk of mixture remains below a critical threshold of 1.

Crucially, the “MAF_ceiling” targets predominately components that significantly contribute to a mixture’s risk, potentially requiring regulatory actions to reduce the exposure or refine the hazard and/or exposure assessments only for these chemicals. Conversely, the so-called “MAF_factor” approach could impose similar regulatory requirement also on substances with minimal contribution to combined toxicity, which may lead to disproportionate regulatory actions on low-risk substances without leading to any appreciable risk reduction. The regulatory application of “MAF_ceiling” would require a larger factor than a “MAF_factor” but would impact fewer substances. "The University of Gothenburg led work to evaluate different MAF classes from a regulatory perspective, providing insights into their comparative effectiveness and implications", highlights Thomas Backhaus, professor from the University of Gothenburg.

Implementation of MAF in the regulatory frameworks

An overview ↗ of the current state of the MAF discussions and positions from regulatory authorities, academia, civil society organisations and industry has been published. This compilation underscores varying perspectives, with civil society strongly advocating for the adoptation of the MAF, while business associations express economic concerns. European regulatory authorities, with some notable exceptions, generally offer cautious support but are also clearly waiting for more details to emerge. However, there seem to be a large agreement that the MAF_factor is not a suitable regulatory instrument, due to its potential to penalise chemicals with minimal contribution to the mixture risk.

The Austrian Agency for Health and Food Safety and the University of Basel under the PARC’s activities ‘Innovation in regulatory risk assessment’ is currently implementing various case studies on typical mixtures in environmental and human contexts. These studies further evaluate the different approaches from a regulatory perspective and estimate the MAF sizes that effectively protect human health and the environment without being unnecessarily stringent. The results of these studies will be published soon and then shared with the PARC partners.