Internal Workshop: What is a mixture?

This subproduct was an internal workshop/round table discussion. We discussed "what is a mixture?" across the different program offices and scientific disciplines. We also discussed methods commonly used in the epidemiological literature to analyze environmental mixtures (both chemical and non-chemical) in relation to cumulative health outcomes and the potential for inclusion of these studies in scientific health assessments. 

Impact/Purpose

Importance of the Topic: As noted in the Cumulative Impacts: Recommendations for ORD Research report, “the single pollutant/single exposure paradigm is not well suited to the reality that individuals, communities, and tribes are exposed to numerous pollutants from a wide array of sources through multiple media and pathways over time.” And that these pollutant exposures are accompanied by exposures to non-chemical stressors that can alter their impacts. There is a growing interest in cumulative impacts from both policy guidance and scientific understanding needs. However, the variety of scientific disciplines, approaches, and goals of research in this area can lead to confusion and crosstalk without understanding of the varying jargon for mixtures.  Current State of the Topic: The word “mixture” is frequently used, but the meaning varies between scientific disciplines. While “chemical mixture” has been defined in Agency Guidelines since 1986, the modern concept of mixtures has expanded to include physical, non-chemical, climate, and/or social stressors. In the context of cumulative impacts, understanding how different disciplines approach, measure, analyze, and interpret mixtures would benefit understanding across the Agency and allow for improved communication with stakeholders.  Desired State of the Topic: To quantify the definition of “mixture” across different scientific disciplines and/or different offices or programs within the Agency. What is Needed to Bridge the Gap Between Current and Desired States: This initial workshop will bring together a small group of EPA scientists to begin the discussion on what is a mixture and to help develop a better understanding of the jargon used to describe mixtures. This short-term goal, of creating a working definition of what a mixture is, will also help in identifying StRAP products and sub-products that may be addressing a similar research question from different scientific discipline perspectives or approaches. This in turn will help build cohesion and collaborations across these projects. A working definition of mixtures will also provide the foundation to develop a “best practices” document for consideration for how different scientific disciplines and offices and programs across the Agency. In the long-term, there are many topics surrounding mixtures research that would benefit from well-balanced perspectives. Topics include but are not limited to: mixtures in the context of cumulative impacts; environmental justice; mixtures across different media and contexts (e.g., water, air, built environment, etc.); analytical and/or statistical methods; and applications of mixtures in research and interpretation of results for scientific health assessments. These topics have the potential to lead to a series of future discussions, roundtables, workshops, and/or seminars.  This workshop is a starting point for discussing mixtures among Agency scientists. While this initial workshop is among internal Agency scientists, moving forward we would also like to include partners and policy makers, both internal and external to the Agency. We designed this workshop to engage participants in interdisciplinary problem formulation and to develop a shared multidimensional understanding of (1) how different scientific disciplines define “mixtures”; (2) what types of methods are used to analyze mixtures among the different scientific disciplines; and (3) how can we best communicate the differences in jargon to scientists across the Agency. The proceedings from this workshop will help to further research problem formulation approach to improve understanding of knowledge gaps.

Citation

Krajewski, A. AND K. Rappazzo. Internal Workshop: What is a mixture? Internal workshop: What is a mixture, Virtual, NC, July 29, 2024.