Environmental Forensic Investigation of Ethylene Oxide Sterilization Emissions, Air Dispersion Modeling, and Community Exposure Assessment
Project Overview
Air dispersion modeling plays a central role in environmental forensic investigations involving medical sterilization facilities because it provides a scientifically accepted method for reconstructing historical airborne contaminant concentrations when direct environmental monitoring data are limited, unavailable, or collected after the relevant exposure period. Facilities that use ethylene oxide (EtO) for sterilization may emit contaminants through stack discharges, building ventilation systems, process vents, and fugitive pathways associated with sterilization and aeration operations. Evaluating potential community exposure from these facilities therefore requires integrating engineering source characterization, atmospheric science, meteorological observations, terrain, receptor mapping, and quantitative exposure assessment within a technically defensible scientific framework capable of reconstructing historical ambient concentrations over extended periods (U.S. EPA, 2017; American Meteorological Society & U.S. EPA, 2019).
RoseyFields conducted a comprehensive environmental forensic investigation involving a medical sterilization facility to evaluate historical airborne exposure associated with EtO sterilization emissions and to assess how alternative source representations influenced predicted concentrations in surrounding residential communities. The investigation extended beyond preparation of a single regulatory air model by evaluating multiple technically reasonable emission scenarios representing different assumptions regarding the release configuration of sterilization emissions. This approach is especially important in environmental forensic analyses involving sterilization facilities because historical emissions may originate from more than one type of release mechanism, and the selection of source geometry can materially influence modeled ground-level concentrations. By incorporating engineering source characterization, receptor mapping, and atmospheric dispersion modeling into a unified analytical framework, the investigation provided a more robust assessment of potential off-site exposure than would have been possible using a single deterministic modeling scenario alone (ASTM International, 2021; U.S. EPA, 2017).
A principal focus of the investigation involved evaluating the spatial relationship between facility emissions and nearby residential receptors. Community exposure assessments involving hazardous air pollutants require more than generalized modeling contours; they also require understanding where potentially exposed populations live relative to modeled concentration gradients and how those concentrations may vary under alternative source and meteorological assumptions. Geographic information systems (GIS), receptor mapping, and source-to-receptor analysis are therefore important tools in environmental forensic investigations because they help connect modeled airborne transport to real-world residential exposure settings. Integrating atmospheric modeling with receptor-based spatial analysis allowed the investigation to evaluate potential exposure patterns across nearby neighborhoods rather than limiting the assessment to the facility boundary or a small number of isolated receptors (National Academies of Sciences, Engineering, and Medicine, 2022; U.S. EPA, 2017).
The investigation was designed as a multidisciplinary environmental forensic assessment rather than a narrow compliance exercise. Engineering source characterization, atmospheric dispersion modeling, sensitivity analysis, receptor mapping, and exposure reconstruction were considered together to evaluate the robustness of historical exposure estimates under multiple technically plausible conditions. This type of integrated approach is consistent with accepted environmental forensic practice because it allows investigators to evaluate not only whether modeled concentrations occur, but also how those concentrations depend on source assumptions, meteorological conditions, terrain, and the location of nearby residents. By combining these multiple lines of evidence, RoseyFields developed a scientifically supported framework for evaluating historical airborne exposure associated with sterilization emissions while preserving complete confidentiality regarding the underlying project (ASTM International, 2021; National Academies of Sciences, Engineering, and Medicine, 2022).
Chemicals of Concern
The principal chemical of concern in this investigation was ethylene oxide, a highly reactive, colorless gas used extensively as a low-temperature sterilant for medical devices and healthcare products that cannot be sterilized using conventional steam or high-temperature methods. EtO has long been used because of its ability to penetrate complex packaging materials and effectively eliminate bacteria, fungi, viruses, and spores without damaging heat-sensitive equipment. At the same time, EtO is also recognized as a hazardous air pollutant and human carcinogen, making the evaluation of historical emissions and potential community exposure an important component of environmental forensic investigations involving commercial sterilization facilities (U.S. EPA, 2016; International Agency for Research on Cancer, 2012).
Unlike contaminants that persist primarily in soil or groundwater, EtO exists predominantly in the atmosphere following release and is transported by prevailing meteorological conditions. Wind speed, wind direction, atmospheric stability, mixing height, terrain, and local aerodynamic effects can all influence the transport and dilution of airborne EtO. As a result, historical community exposure generally cannot be reconstructed through environmental sampling alone and instead requires atmospheric dispersion modeling combined with engineering source characterization and emissions reconstruction. This reliance on air modeling makes EtO investigations especially sensitive to the quality of source characterization and the assumptions used to represent how emissions enter the atmosphere (U.S. EPA, 2017; American Meteorological Society & U.S. EPA, 2019).
Medical sterilization facilities may release EtO through several different mechanisms depending on facility design, process configuration, and control technologies. Potential release pathways can include dedicated exhaust stacks, sterilization chamber vents, aeration room exhausts, abatement-system discharges, building ventilation releases, and diffuse or fugitive emissions associated with indoor handling and process losses. Because uncertainty often exists regarding the relative contribution of these different pathways, environmental forensic investigations commonly evaluate multiple source representations rather than relying upon a single release configuration. Testing alternative source geometries—such as elevated point sources and distributed area sources—can provide important insight into how engineering assumptions influence predicted ground-level concentrations and can substantially strengthen the technical defensibility of exposure reconstruction (U.S. EPA, 2022; ASTM International, 2021).
The toxicological significance of EtO further underscores the importance of reconstructing historical airborne concentrations with care. Numerous scientific and regulatory evaluations have identified EtO as a carcinogenic inhalation hazard, and regulatory agencies have devoted substantial attention to understanding emissions from commercial sterilization facilities and their implications for nearby communities. In environmental forensic investigations, the objective is not merely to acknowledge that EtO is hazardous, but to determine how historical facility emissions may have been transported through the atmosphere, whether modeled concentrations remain consistent across technically reasonable scenarios, and how those predicted concentrations align with nearby residential populations. Integrating toxicology with atmospheric modeling, engineering evaluation, and receptor analysis therefore provides a more rigorous framework for evaluating long-term community exposure than would be possible through any single discipline alone (U.S. EPA, 2016; Kirman & Hays, 2017).
Methods
A comprehensive environmental forensic investigation was conducted to evaluate historical airborne exposure associated with sterilization emissions using accepted methodologies from environmental engineering, atmospheric science, regulatory air dispersion modeling, GIS-based receptor analysis, and exposure assessment. The investigation integrated engineering source characterization, atmospheric dispersion modeling files, source and receptor geometry, mapped residential receptor information, and conceptual exposure reconstruction to evaluate how emissions from a sterilization facility may have affected nearby communities over time. Rather than relying on a single deterministic air model, the investigation evaluated multiple technically reasonable source representations in order to assess how predicted concentrations varied under alternative assumptions regarding the manner in which emissions entered the atmosphere. This use of sensitivity analysis is an important component of environmental forensic investigations because it allows modelers to determine whether overall exposure conclusions remain robust despite uncertainty in source configuration (U.S. EPA, 2017; ASTM International, 2021).
The investigation began with engineering review and source characterization of the sterilization facility. Potential release pathways were evaluated in the context of typical EtO sterilization operations, including elevated exhaust releases and more diffuse facility-related emissions. Source characterization is a critical first step in air dispersion modeling because source geometry, release height, exhaust temperature, exit velocity, and the physical footprint of the release all influence plume rise, dilution, and ground-level concentration patterns. In sterilization cases, uncertainty often exists regarding the relative contribution of stack emissions, building ventilation discharges, and fugitive losses; accordingly, the investigation evaluated multiple representative source configurations to test whether modeled community exposure remained consistent under more than one technically plausible emissions scenario (U.S. EPA, 2022; American Meteorological Society & U.S. EPA, 2019).
Atmospheric dispersion modeling was then evaluated using AERMOD-based modeling methodologies consistent with current U.S. Environmental Protection Agency guidance. AERMOD is widely used in regulatory and forensic investigations because it incorporates source parameters, terrain, atmospheric stability, wind speed, wind direction, and other meteorological factors to estimate ambient air concentrations at discrete receptor locations. The modeling framework included near-field and broader off-site receptor networks so that concentration gradients could be evaluated both close to the facility and throughout the surrounding community. Receptors were terrain-adjusted to reflect local elevation and hill-height conditions, which can influence plume behavior and predicted ground-level concentrations even in areas without dramatic topographic relief. Incorporating terrain and a nested receptor structure strengthened the realism of the modeling analysis by allowing the investigation to evaluate both localized near-source impacts and broader community-scale exposure patterns (U.S. EPA, 2017; American Meteorological Society & U.S. EPA, 2019).
A distinguishing feature of the investigation was the integration of receptor mapping and residential exposure analysis into the modeling framework. Rather than treating the air model as an abstract technical exercise, the investigation evaluated nearby residential locations in relation to the modeled source and receptor domain. GIS-based source-to-receptor analysis was used to consider the spatial relationship between facility emissions and surrounding residential neighborhoods, which is an essential component of environmental forensic exposure reconstruction. Linking modeled concentration fields to nearby residences improves the scientific usefulness of the analysis because it allows investigators to evaluate not only whether elevated concentrations occur, but whether those concentrations overlap spatially with actual potentially exposed populations. This type of receptor-based analysis is particularly important in toxic tort and community exposure investigations involving hazardous air pollutants such as EtO (National Academies of Sciences, Engineering, and Medicine, 2022; U.S. EPA, 1989).
The investigation also incorporated sensitivity analysis through evaluation of alternative source geometries representing different engineering assumptions regarding sterilization emissions. One modeled scenario represented emissions using a distributed facility-related source configuration consistent with a more diffuse release pathway, while another scenario represented emissions as an elevated point-source release with stack-like characteristics. Comparing these scenarios allowed the investigation to assess how source geometry influenced plume transport, near-field concentration gradients, and the spatial pattern of potential community exposure. This type of scenario testing is particularly valuable in environmental forensic analyses because it helps identify whether predicted exposure patterns are driven by the underlying emissions behavior of the facility or by a single modeling assumption chosen at the outset. By evaluating multiple technically plausible source configurations, the investigation substantially strengthened the defensibility of the exposure reconstruction (ASTM International, 2021; U.S. EPA, 2017).
Finally, modeled concentrations were interpreted within a broader environmental forensic framework that integrated engineering source assumptions, atmospheric science, GIS-based receptor analysis, and accepted exposure-assessment principles. Rather than relying upon one line of evidence alone, the investigation considered how source characterization, receptor placement, terrain, and alternative modeling scenarios collectively influenced the interpretation of historical airborne exposure. This multidisciplinary methodology is consistent with accepted environmental forensic practice because it emphasizes the integration of engineering, atmospheric modeling, exposure science, and uncertainty analysis to reconstruct historical community exposure in a scientifically rigorous and technically defensible manner (ASTM International, 2021; National Academies of Sciences, Engineering, and Medicine, 2022).
Results
The environmental forensic investigation demonstrated that historical sterilization emissions can be evaluated using a modeling framework that meaningfully captures both facility-scale plume behavior and the spatial relationship between emissions and nearby residential receptors. By integrating alternative source representations, nested receptor grids, terrain-adjusted receptor elevations, and GIS-based residential mapping, the investigation provided a scientifically grounded basis for evaluating potential off-site exposure associated with sterilization emissions. The use of multiple technically reasonable source scenarios was particularly important because it allowed the investigation to test whether predicted exposure patterns remained generally consistent despite differences in source geometry and release assumptions. This substantially improved the robustness of the exposure reconstruction relative to a single deterministic modeling approach (U.S. EPA, 2017; ASTM International, 2021).
Comparison of alternative source representations demonstrated that engineering assumptions regarding the release pathway can materially influence predicted ground-level concentrations, especially in the near field surrounding a sterilization facility. Distributed or area-type source representations are useful for evaluating diffuse or fugitive emissions associated with building ventilation, broad process areas, or uncertain release locations, whereas elevated point-source representations are more appropriate for stack-like discharges characterized by a defined release height, exit velocity, and exhaust temperature. Because these source types interact differently with atmospheric turbulence and plume rise, they can produce different concentration gradients near the source even when the underlying emissions mass is similar. Evaluating both source representations therefore provided important context for interpreting model sensitivity and helped ensure that exposure conclusions were not dependent on a single assumed release configuration (American Meteorological Society & U.S. EPA, 2019; U.S. EPA, 2017).
The receptor structure also strengthened the technical rigor of the investigation by allowing evaluation of both near-source impacts and broader neighborhood-scale exposure patterns. Dense receptor spacing in the immediate vicinity of a facility is especially important in EtO investigations because the highest modeled concentrations frequently occur close to the source where plume interception, limited dilution, and building-related turbulence may affect ground-level concentrations. Broader receptor spacing at larger distances is then necessary to evaluate how modeled concentrations attenuate across surrounding residential areas. This nested receptor framework allowed the investigation to evaluate not only the existence of potential off-site exposure, but also the spatial gradient of modeled concentrations across the community. In an environmental forensic context, that type of receptor structure is important because it supports a more nuanced assessment of community exposure than would be possible using a sparse or overly generalized receptor network (U.S. EPA, 2017; National Academies of Sciences, Engineering, and Medicine, 2022).
Terrain-adjusted receptor evaluation further improved the scientific defensibility of the modeling framework. Even in communities without dramatic terrain relief, receptor elevation and local hill-height relationships can influence how plume centerlines intersect populated areas and where modeled concentrations are predicted to occur. By incorporating terrain-adjusted receptor information, the investigation better represented the physical environment in which emissions dispersed and reduced the likelihood that modeled concentrations would be interpreted without regard to the local topographic setting. This is particularly important in historical exposure reconstruction because even modest terrain variation can influence the relative location of maximum ground-level concentrations under certain meteorological conditions (American Meteorological Society & U.S. EPA, 2019; U.S. EPA, 2017).
The integration of residential mapping into the modeling framework also provided an important line of evidence regarding potential community exposure. Environmental forensic investigations are most informative when modeled concentration fields are interpreted in relation to the actual locations of nearby residents rather than solely as abstract contour plots. GIS-based source-to-receptor evaluation allowed the investigation to examine whether modeled concentration patterns overlapped with nearby residential areas and whether the receptor network adequately represented the surrounding community. This type of residence-focused spatial analysis is especially valuable in EtO investigations because it helps translate engineering and atmospheric modeling outputs into a framework relevant to long-term human exposure and community risk evaluation (National Academies of Sciences, Engineering, and Medicine, 2022; U.S. EPA, 1989).
Overall, the investigation demonstrated that evaluating historical EtO sterilization emissions requires more than simply running a regulatory air model. It requires integrating source characterization, sensitivity analysis, receptor design, terrain evaluation, and residential mapping to determine whether predicted concentration patterns remain scientifically defensible across multiple technically plausible scenarios. By synthesizing engineering evaluation, atmospheric modeling, GIS-based receptor analysis, and exposure reconstruction, the investigation developed a comprehensive environmental forensic framework for evaluating historical community exposure associated with sterilization emissions. This multidisciplinary approach reduced uncertainty, improved the interpretability of modeled concentration patterns, and provided a technically rigorous basis for environmental consulting, toxic tort litigation, and expert witness services involving historical EtO emissions and community exposure (ASTM International, 2021; National Academies of Sciences, Engineering, and Medicine, 2022).
Conclusions
This environmental forensic investigation demonstrated that robust evaluation of historical EtO sterilization emissions requires a multidisciplinary scientific approach that extends beyond a single regulatory air model. By integrating engineering source characterization, atmospheric dispersion modeling, GIS-based receptor analysis, residential mapping, and exposure reconstruction, the investigation developed a comprehensive understanding of how sterilization emissions may have been transported through the atmosphere and how modeled concentration patterns related to nearby residential communities. This integrated framework is consistent with accepted environmental forensic practice and provides a more scientifically defensible basis for evaluating historical community exposure than reliance upon any one dataset or modeling assumption in isolation (ASTM International, 2021; U.S. EPA, 2017).
A principal finding of the investigation was the importance of sensitivity analysis in reconstructing historical exposure associated with sterilization emissions. Evaluating alternative source geometries demonstrated that engineering assumptions regarding the release pathway can materially influence predicted concentration patterns, particularly in the near field surrounding a facility. Systematically testing more than one technically plausible source representation allowed the investigation to identify the role of source geometry in plume behavior while confirming that the broader exposure framework remained grounded in accepted atmospheric modeling principles. Sensitivity analysis therefore served not only as a measure of uncertainty but also as an important quality-assurance tool that strengthened confidence in the overall exposure assessment (American Meteorological Society & U.S. EPA, 2019; ASTM International, 2021).
The investigation also highlighted the value of integrating modeled concentration fields with nearby residential receptors and community geography. Air dispersion modeling is most informative in environmental forensic investigations when predicted concentrations are evaluated in relation to actual populations rather than treated solely as abstract contour outputs. By incorporating receptor mapping and source-to-receptor spatial analysis into the modeling framework, the investigation improved the scientific basis for assessing long-term community exposure and strengthened the interpretability of the results in a human-exposure context. This type of receptor-based analysis is particularly important for hazardous air pollutants such as EtO, where the ultimate objective of the investigation is to understand how facility emissions may have affected nearby residents over time (National Academies of Sciences, Engineering, and Medicine, 2022; U.S. EPA, 1989).
This case study highlights the important role of environmental forensic science in evaluating historical EtO emissions and reconstructing long-term community exposure near sterilization facilities. By integrating engineering analyses, atmospheric dispersion modeling, GIS, receptor mapping, sensitivity analysis, and exposure assessment, RoseyFields provides scientifically rigorous evaluations capable of supporting environmental consulting, regulatory investigations, toxic tort litigation, and expert witness services involving hazardous air pollutants and historical industrial emissions. These multidisciplinary investigations provide objective, evidence-based scientific analyses that improve understanding of airborne contaminant transport, long-term exposure, and the technical reliability of historical air-modeling conclusions while remaining consistent with accepted engineering practice, current environmental science, and evolving regulatory guidance (ASTM International, 2021; National Academies of Sciences, Engineering, and Medicine, 2022).
This investigation was conducted under the direction of Dr. Paul Rosenfeld, an environmental scientist and environmental forensic expert with extensive experience in ethylene oxide investigations, air dispersion modeling, sensitivity analysis, source characterization, and community exposure reconstruction. Dr. Rosenfeld’s work includes complex environmental matters involving historical industrial air emissions, fugitive and point-source releases, building and terrain influences on plume behavior, GIS-based receptor analysis, and the integration of engineering records, environmental monitoring, and atmospheric modeling to evaluate long-term community exposure. Through RoseyFields LLC, Dr. Rosenfeld provides environmental forensic analysis, environmental due diligence, regulatory and compliance support, remediation evaluation, toxic tort and personal injury case assessment, and expert witness testimony involving ethylene oxide contamination, hazardous air pollutant emissions, air-dispersion sensitivity analyses, source attribution, and long-term environmental and human health risks associated with historical industrial operations (ASTM International, 2021; U.S. EPA, 2017).
References
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U.S. Environmental Protection Agency. (2022). National emission standards for hazardous air pollutants for ethylene oxide commercial sterilization facilities. U.S. Environmental Protection Agency.