A group of chemists has proposed adding a new “mixture allocation factor” to EU chemicals rules so regulators account for the combined effects of multiple substances present in the environment.
Concerns about the effects of industrial chemicals, pesticides and pharmaceuticals on ecosystems and human health have been rising, the European Commission’s Science for Environment Policy service said in a release on Friday.
The EU’s Chemicals Strategy for Sustainability sets out an ambition for a pollution-free environment by 2050.
The proposal comes as chemical risk management at European level is under review, with no major changes to the EU’s main chemicals law — the REACH regulation — expected in the near future.
REACH is the EU framework for registering and controlling chemicals to protect human health and the environment.
Researchers argued that current approaches focus mainly on single substances and intentional mixtures, but do not properly account for “coincidental mixtures” that occur when a new chemical enters an environment where other chemicals already exist. They set out their proposal in a policy paper published in "Science."
A “risk cup” to assess combined exposure
The scientists suggested using a “risk cup” model — a concept originally developed by the US Environmental Protection Agency for assessing cumulative pesticide risks — to represent the way separate chemical exposures can add up, the EU service said.
Under this approach, chemicals might each be within their individual safety limits, but together exceed an overall threshold when combined in a single “cup.”
Their suggested “mixture allocation factor” would act as a correction when assessing each chemical on its own, and would be used to identify substances contributing most to combined risk.
In an example with five chemicals, the maximum mixture allocation factor would be 5, meaning each substance could take up one-fifth of the "risk cup."
Chemicals assigned a mixture allocation factor above 1 would be treated as higher-risk because they would push the combined exposure beyond the overall limit, the researchers argued.
They said this would concentrate additional controls on the chemicals contributing most to mixture-related risk, while leaving lower-risk substances less affected.
The team added the approach could be introduced first for industrial chemicals and later extended to pesticides and pharmaceuticals.
The researchers also flagged that a key regulatory question would be how to set the size of the mixture allocation factor — effectively, how large the “risk cup” should be — balancing protection of people and ecosystems against unnecessary changes to existing assessments.
They suggested starting with a modest factor and revising it as more data become available.
The study did not present new primary data, but offered a regulatory proposal intended to be incorporated into REACH without requiring detailed mixture calculations for thousands of chemicals, the Science for Environment Policy update said.
