Chemical Mixtures Assessment

In collaboration with VITO, we analyzed environmental monitoring and human biomonitoring data to gain a deeper understanding of realistic co-exposure to chemicals and evaluate associated risks. Our findings revealed that mixtures in the environment are largely influenced by spatial processes, with complexity increasing from upstream to downstream and under high anthropogenic pressure. Our mixture pressure analysis indicated that the majority of observed mixture exposures do not pose a risk to the environment (81-94% of observed mixtures). For the remaining cases, combined exposure risk estimates are dominated by a few substances and heavily dependent on local factors. We were able to determine which EU Regulations or Directives would be most effective in managing these mixtures of concern. Our research concludes that a potential Mixture Assessment Factor (MAF) should be proportional to the magnitude of the identified mixture toxicity problem. For human exposure, only a small number of compounds are typically covered in monitoring studies, making it difficult to evaluate co-exposure patterns. While it is hard to draw robust conclusions because of the diversity in existing mixture risk studies, the available studies suggest that a small number of compounds tend to drive toxicity.

For more information, please download the final report below and review the technical annexes A-D (environment) and technical annex E (human).

Four different published MAF calculation methods were evaluated using freshwater monitoring data from 5 datasets. The robustness of each method was analyzed in terms of: (1) the choice of reference value (i.e. PNEC or HC5); (2) sample size and the presence of unknown and non-detected substances; (3) the consideration of mixtures with single substance risk and (4) the choice of protection level and level of conservatism. Which method takes preference is partly a policy decision, but analyses like these help inform the decision-making. Based on the set of criteria, the Maximum Cumulative Ratio method was found to be the most robust and reliable.

The assessment suggests that in a reasonable worst-case (ca. 90th percentile), a factor of 3 is sufficient to eliminate exposure concerns in most cases, but it is important to note that there can be significant differences between MAF methods. Therefore, future MAF calculations should use a robust method that takes these differences into account. The choice of method is partly a policy decision, but studies like this help inform the decision-making process.