Chemical Mixture Risk Assessment:
May 31, the European Chemical Industry Council (Cefic) unveiled a tool for assessing the risks posed by chemical combinations: the Maximum Cumulative Ratio (MCR) (see e.g., news release, combination effects tools). MCR compares the toxicity of individual chemicals to the cumulative toxicity of all chemicals in an exposure scenario. Cefic argues that in most exposure scenarios the risk of one or two chemicals contribute nearly all risk of harm. The organization notes that prioritization of chemical combinations is necessary to identify combinations of concern that warrant full risk assessment.
Cefic references Maximum Cumulative Ratio (MCR) as a Tool for Assessing the Value of Performing a Cumulative Risk Assessment (in International Journal of Environmental Research and Public Health) for full discussion of the application of MCR. The article comprises an investigation of the magnitude of toxicity from multiple chemical exposure that is missed in scenarios where no cumulative risk assessment is conducted. U.S. Geological Survey water quality data were used for the evaluation. From 5 to 81 chemicals were present in the 3,000 samples analyzed. The authors estimate that approximately 20 percent of cumulative toxicity –compared to component chemical toxicity– is missed where cumulative risk assessments are not conducted. However, mixture toxicities were dominated by only a fraction of chemical compounds present.
Because risk is usually driven by one or two chemicals in a combination, Cefic believes that controlling individual substances through the current regulatory schemes will often control the risk from combination exposures.
Cefic notes that MCR is based on the WHO risk assessment framework (see e.g., Combined Exposure Risk Assessment Workshop Report) and relies on cumulative risk assessment theories from the European Scientific Committees (see e.g., Environmental Risk Assessment of Mixtures Symposium).