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Title: Enhancing the Chemical Mixture Methodology in Emergency Preparedness and Consequence Assessment

Emergency preparedness personnel at US Department of Energy (DOE) facilities use the chemical mixture methodology (CMM) to estimate the potential health impacts to workers and the public from the unintended airborne release of chemical mixtures. The CMM uses a Hazard Index (HI) to compare a chemical’s concentration at a receptor location to an appropriate concentration limit for that chemical. This limit is typically based on Protection Action Criteria (PAC) values developed and published by the DOE. As a first cut, the CMM sums the HIs for all the chemicals in a mixture to conservatively estimate their combined health impact. A cumulative HI ≥ 1.0 represents a concentration at or exceeding the concentration limit and indicates the potential for adverse health effects. Next, health code numbers (HCNs) are used to identify the target organ sets that may be impacted by exposure to each chemical in a mixture. The sum of the HIs for the maximally impacted target organ set is used to provide a refined, though still conservative estimate, of the potential for adverse health effects from exposure to the chemical mixture. This paper explores approaches to further enhance the effectiveness of the CMM by using HCN weighting factors to reducemore » over-conservatism. A series of 24 case studies have been defined to evaluate both the existing CMM and three new approaches for improving the CMM. The first approach uses a set of HCN weighting factors that are applied based on the priority ranking of the HCNs for each chemical. The second approach uses weighting factors based on the priority rankings of the HCNs established for a given type of concentration limit. The third approach uses information on the exposure route used to derive PAC values and the second approach’s HCN ranking to derive and apply its HCN weighting factors. Initial testing indicates that applying weighting factors reduces the over-conservatism in the CMM for certain types of chemical mixtures, though care must be taken to avoid introducing non-conservative results. In the near future, additional testing and analysis will be conducted that will lead to the adoption of one of the tested approaches into the CMM. The long-term goal is to develop and implement a more comprehensive approach that will take into account the specific health effects that were observed during the studies used to derive the chemical-specific concentration limits used in the CMM.« less
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Resource Type:
Journal Article
Resource Relation:
Journal Name: Toxicology, 313(2-3):174-184
Research Org:
Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
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Country of Publication:
United States
chemical mixture methodology; health code numbers; weighting factors; acute health effects; exposure route; protection action criteria