Regulatory and practical considerations on the implementation of a mixture allocation factor in REACH

There is indisputable evidence that the environment, humans and wildlife are continuously exposed not to single but to multiple chemicals from different sources. Exposure to these mixtures can lead to combined risks not yet sufficiently addressed in any of the European chemical legislations. Under the REACH regulation for industrial chemicals, specific environmental mixture assessments are challenged by a lack of data on toxicity, use and exposures and the communication of data along the supply chain. Within the Chemicals Strategy for Sustainability the European Commission proposed to introduce (a) mixture allocation factor(s) (MAF) as regulatory management tool to reduce exposures, effects and potential risks of unintentional mixtures. The MAF is proposed to be applied as default value within the chemical safety assessments undertaken by companies under REACH. Here, we critically review the relevant literature discussing the conceptual background of the MAF and approaches to derive its magnitude. The analysis focuses on the environment and key issues for an implementation in regulatory practise together with remaining uncertainties and needs for possible ways forward. At this stage introducing a MAF in REACH Annex I appears the most pragmatic and immediately implementable measure to address risks from unintentional mixtures in the environment. A so-called MAF_ceiling appears as the preferred option of policy makers, since it would only affect relevant substances close to their respective risk threshold. While the magnitude of a MAF will be decided politically, the choice of methods and assumptions to derive its size should be clear and transparent, build on the available scientific evidence and take account for uncertainties. A MAF will be most effective reducing environmental releases and exposure levels if risk mitigation measures are implemented in practise. Its socioeconomic impacts and costs need to be assessed in a balanced way together with the benefits for the environment, society, and for companies—also in comparison to the efforts needed for specific mixture risk assessments. In the future and with the experiences gathered in practise, a discussion is needed on how to assess and regulate unintentional mixtures across different pieces of chemicals legislation to consider the true exposure situation and ensure harmonisation.