August 1, 2014.
The Chemical Mixture Methodology (CMM) is a tool used to assess potential hazardous health impacts of the release of chemical mixtures into the atmosphere. Furthermore, the CMM helps determine if these potential adverse toxic effects will affect an individual’s ability to take protective actions in an emergency. The CMM first calculates the Hazard Index (HI) of each chemical then adds the individual HIs together. If the value of the summed HI is >1.0 further examination is warranted. To do so, Health Code Numbers (HCNs), that are similar to medical diagnostic codes, are used to group toxic effects targeting the same organ or organ system. HCNs are sorted using Target Organ System Effect and Specific Target Organ Effect to examine which target organs are likely to be affected. To accommodate severity, the HCN for respiratory irritation was expanded into three categories: severe, moderate, and mild. To make the CMM more realistic, weighting factors of “1”, “0.5”, and “0.25” are applied to the HIs of severe, moderate, and mild irritants respectively. Using 127 test cases with three concentration scenarios, extensive testing is conducted to investigate if there is any benefit using the improved respiratory irritant HCNs. By refining the respiratory irritants to severe, moderate, and mild categories and applying weighting factors, the conservatism has been reduced. In 23% of test cases benefit increased and none decreased in benefit. Currently the user’s guides for the CMM Workbook and Wizard are being updated to include the aforementioned modifications. PNNL-SA-104175
Pacific Northwest National Laboratory (PNNL)
This material is based upon work supported by the S.D. Bechtel, Jr. Foundation and by the National Science Foundation under Grant No. 0952013. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the S.D. Bechtel, Jr. Foundation or the National Science Foundation. This project has also been made possible with support of the National Marine Sanctuary Foundation. The STAR program is administered by the Cal Poly Center for Excellence in Science and Mathematics Education (CESaME) on behalf of the California State University (CSU).