PUBLICATION | Evans et al 2015. How wide should the scope be for mixture risk assessment?

Should the scope of human mixture risk assessment span legislative/regulatory silos for chemicals?, Science of The Total Environment, RM Evans, OV Martin, M Faust, A Kortenkamp. Available online 10 November 2015, ScienceDirect (open-access)

Our recently accepted paper discusses whether the scope of a mixture risk assessment needs to include chemicals and/or effects that are subject to different pieces of legislation (which we defined as ‘silos’). We present illustrations of multiple situations in which it is entirely plausible that the risk to human health can only be accurately predicted by considering multiple chemicals across multiple silos – however this is almost never done, and nor is there a legislative framework for doing so. We propose the discussion of various options, ranging from small, incremental changes based on existing legislation and practice, up to larger, more ambitious proposals for new legislation.

We hope to promote discussion and would welcome comments via this blog, through email or via the full text paper.


Current chemicals regulation operates almost exclusively on a chemical-by-chemical basis, however there is concern that this approach may not be sufficiently protective if two or more chemicals have the same toxic effect. Humans are indisputably exposed to more than one chemical at a time, for example to the multiple chemicals found in food, air and drinking water, and in household and consumer products, and in cosmetics. Assessment of cumulative risk to human health and/or the environment from multiple chemicals and routes can be done in a mixture risk assessment (MRA). Whilst there is a broad consensus on the basic science of mixture toxicology, the path to regulatory implementation of MRA within chemical risk assessment is less clear.

In this discussion piece we pose an open question: should the scope of human MRA cross legislative remits or ‘silos’? We define silos as, for instance, legislation that defines risk assessment practice for a subset of chemicals, usually on the basis of substance/product, media or process orientation. Currently any form of legal mandate for human MRA in the EU is limited to only a few pieces of legislation. We describe two lines of evidence, illustrated with selected examples, that are particularly pertinent to this question: 1) evidence that mixture effects have been shown for chemicals regulated in different silos and 2) evidence that humans are co-exposed to chemicals from different silos. We substantiate the position that, because there is no reason why chemicals allocated to specific regulatory silos would have non-overlapping risk profiles, then there is also no reason to expect that MRA limited only to chemicals within one silo can fully capture the risk that may be present to human consumers. Finally, we discuss possible options for implementation of MRA and we hope to prompt wider discussion of this issue.

You can read the full text for free (open access) here.


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