Environmental Forensic Investigation of Historical Ethylene Oxide Emissions, Air Dispersion Modeling, and Community Exposure Assessment
Project Overview
Ethylene oxide (EtO) is a highly reactive industrial chemical widely used in the production of specialty chemicals, polymers, surfactants, and sterilized medical products. Although EtO has substantial commercial and industrial importance, it has also become the focus of increasing environmental and public health interest because of its classification as a human carcinogen and the development of increasingly health-protective regulatory risk assessment methodologies. Evaluating historical community exposure to EtO requires a multidisciplinary scientific approach integrating atmospheric science, environmental engineering, industrial process evaluation, emissions inventory development, air dispersion modeling, environmental chemistry, epidemiology, toxicology, and quantitative human health risk assessment. Because EtO is present in both anthropogenic emissions and measurable background concentrations, distinguishing facility contributions from regional and naturally occurring sources presents one of the most technically challenging aspects of environmental forensic investigations (U.S. EPA, 2016; ATSDR, 1990).
RoseyFields conducted a comprehensive environmental forensic investigation involving historical EtO emissions from multiple industrial facilities operating within a heavily industrialized region. The primary objectives were to reconstruct historical emissions over several decades, evaluate changing emission inventories across numerous industrial sources, estimate ambient EtO concentrations using regulatory air dispersion modeling, compare modeled concentrations with available environmental monitoring data, and assess the scientific evidence regarding potential human health impacts associated with long-term environmental exposure. The investigation integrated historical emissions inventories, engineering analyses, atmospheric dispersion modeling, environmental monitoring, epidemiological literature review, and quantitative risk assessment to develop a scientifically supported understanding of historical community exposure while carefully evaluating uncertainty associated with both emissions reconstruction and environmental measurements (U.S. EPA, 2017; U.S. EPA, 2024).
A major component of the investigation involved reconstructing historical EtO emissions using multiple decades of emissions inventory information from numerous industrial operations. Historical emissions varied substantially over time because of changing production rates, process modifications, pollution control technologies, reporting methodologies, and facility ownership. Rather than evaluating emissions from a single source, the investigation considered cumulative contributions from multiple industrial facilities together with other potential background sources. Long-term emissions inventories were integrated with engineering evaluations and atmospheric dispersion modeling to estimate historical ambient concentrations under representative operating conditions while accounting for changes in industrial activity over time. This historical reconstruction provided a scientifically robust framework for evaluating potential community exposure throughout multiple decades of industrial operation (U.S. EPA, 2017).
The investigation also evaluated the strengths and limitations of ambient air monitoring for measuring EtO concentrations. Because ambient EtO concentrations frequently approach analytical detection limits, interpreting monitoring results requires careful consideration of method sensitivity, measurement precision, background variability, and analytical uncertainty. Available monitoring data were therefore evaluated together with atmospheric dispersion modeling rather than independently. Consistent with current regulatory practice, air dispersion modeling provided an important tool for estimating long-term ambient concentrations where monitoring data alone were insufficient to characterize historical exposure. The investigation also evaluated monitoring uncertainty, including the influence of method detection limits and background concentrations observed at locations without known industrial EtO sources, emphasizing the importance of integrating environmental monitoring with engineering analyses and atmospheric modeling when evaluating long-term community exposure (U.S. EPA, 2024).
Chemicals of Concern
The principal chemical of concern evaluated during this environmental forensic investigation was ethylene oxide (EtO), a highly reactive organic compound used extensively in chemical manufacturing and in the sterilization of medical equipment and other temperature-sensitive materials. Because of its unique chemical properties, EtO serves as an important industrial intermediate in the production of numerous commercial products. However, EtO has also become one of the most closely studied airborne toxicants due to its classification as a human carcinogen and the development of increasingly protective health-based exposure guidelines. As a volatile organic compound, EtO is emitted directly into the atmosphere where it can disperse over varying distances depending on emission characteristics, meteorological conditions, atmospheric mixing, and chemical degradation processes. Consequently, evaluating airborne EtO requires an integrated understanding of industrial engineering, atmospheric science, environmental chemistry, toxicology, and exposure assessment (U.S. EPA, 2016; ATSDR, 1990).
Unlike persistent contaminants that accumulate in soils or sediments, EtO exists primarily in the atmosphere following release and undergoes degradation through reactions with naturally occurring atmospheric oxidants, including hydroxyl radicals. Although its atmospheric lifetime is relatively short compared to many persistent pollutants, continuous industrial emissions may contribute to chronic ambient concentrations in surrounding communities when facilities operate over extended periods. Environmental concentrations therefore depend upon both emission rates and meteorological factors such as wind direction, atmospheric stability, mixing height, temperature, and seasonal variability. Because EtO does not remain localized near emission sources under many atmospheric conditions, evaluating community exposure requires scientifically rigorous atmospheric dispersion modeling supported by representative emissions inventories and meteorological data (U.S. EPA, 2017; World Health Organization, 2003).
The investigation also evaluated the occurrence of background ethylene oxide within ambient air. Scientific studies have demonstrated that measurable EtO concentrations may be detected even in areas without nearby industrial sources because EtO is produced naturally through atmospheric photochemical reactions, biomass combustion, and certain biological processes. In addition, mobile sources and diffuse industrial emissions may contribute to regional background concentrations. Distinguishing facility-related contributions from these background levels is a critical component of environmental forensic investigations because background concentrations may represent a substantial fraction of measured ambient EtO. Proper characterization of background conditions therefore improves interpretation of environmental monitoring data and strengthens source attribution when evaluating potential industrial impacts (U.S. EPA, 2024; Kirman & Hays, 2017).
An important component of this investigation involved evaluating the strengths and limitations of ambient air monitoring for EtO. Because environmental concentrations frequently approach or fall below analytical method detection limits, measured values may exhibit significant uncertainty, particularly at very low concentrations. Analytical precision, sampling duration, instrument sensitivity, background variability, and temporal fluctuations all influence the interpretation of monitoring results. For this reason, environmental monitoring was evaluated together with engineering analyses, historical emissions inventories, and regulatory air dispersion modeling rather than independently. Integrating multiple independent lines of evidence provides a more scientifically robust evaluation of long-term community exposure than reliance upon individual monitoring events alone (U.S. EPA, 2017; U.S. EPA, 2024).
Understanding historical EtO exposure therefore requires a multidisciplinary environmental forensic approach integrating industrial process engineering, emissions reconstruction, atmospheric science, environmental chemistry, toxicology, epidemiology, exposure assessment, and quantitative risk assessment. Combining these scientific disciplines allows investigators to reconstruct historical emission scenarios, evaluate long-term community exposure, distinguish facility-related emissions from regional background concentrations, and develop technically defensible conclusions regarding environmental transport and potential human health risks. This integrated methodology forms the foundation of modern environmental forensic investigations involving airborne hazardous air pollutants and complex industrial emission sources (ASTM International, 2021; National Academies of Sciences, Engineering, and Medicine, 2022).
Methods
A multidisciplinary environmental forensic investigation was conducted to evaluate historical ethylene oxide (EtO) emissions from multiple industrial operations and to characterize long-term community exposure using accepted engineering, atmospheric science, environmental chemistry, toxicology, and quantitative risk assessment methodologies. The investigation integrated historical emissions inventories, regulatory reporting records, process engineering evaluations, air dispersion modeling, ambient air monitoring, geographic information systems (GIS), meteorological analyses, exposure assessment, and epidemiological literature to develop a scientifically supported conceptual model describing historical EtO emissions and their contribution to ambient air concentrations. Rather than relying upon a single dataset, multiple independent lines of evidence were evaluated using a weight-of-evidence framework to characterize historical emissions, assess environmental transport, and evaluate potential human exposure under representative operating conditions (ASTM International, 2021; U.S. EPA, 2017).
The investigation began with a comprehensive review of historical emissions inventories, regulatory filings, engineering documentation, facility operating histories, and available environmental monitoring information. Historical emissions were evaluated across multiple decades to identify temporal trends associated with changing production rates, process modifications, pollution control technologies, and evolving industrial practices. Rather than evaluating individual facilities independently, cumulative regional emissions from multiple industrial operations were reconstructed to better characterize the overall contribution of industrial sources to ambient EtO concentrations. This historical reconstruction provided the basis for developing representative source terms used in subsequent atmospheric dispersion modeling and exposure assessment (U.S. EPA, 2024; U.S. EPA, 2017).
Atmospheric transport was evaluated using regulatory air dispersion modeling techniques consistent with current U.S. Environmental Protection Agency guidance. Engineering analyses incorporated representative source characteristics, emission rates, release parameters, building influences, terrain, and meteorological conditions to estimate ambient EtO concentrations throughout the surrounding region. Historical meteorological datasets were evaluated to characterize prevailing wind direction, atmospheric stability, mixing heights, and seasonal variability that influence contaminant dispersion. Geographic information systems were used to evaluate predicted concentration patterns and compare modeled results with available monitoring information, providing an additional line of evidence for assessing historical community exposure (American Meteorological Society & U.S. EPA, 2019; U.S. EPA, 2017).
Ambient air monitoring data were independently evaluated to assess consistency with modeled concentrations while recognizing the analytical limitations associated with measuring extremely low ambient EtO concentrations. Sampling methodologies, analytical detection limits, temporal variability, background concentrations, and measurement uncertainty were reviewed to determine the reliability of observed monitoring results. Particular attention was given to distinguishing facility-related contributions from regional background concentrations, as measurable EtO may be detected even in areas without nearby industrial sources. Integrating environmental monitoring with engineering analyses and air dispersion modeling provided a more scientifically robust assessment than relying on monitoring data alone, particularly where measured concentrations approached analytical detection limits (U.S. EPA, 2024; Kirman & Hays, 2017).
Finally, quantitative exposure assessment and human health risk assessment were performed by integrating modeled air concentrations, environmental monitoring results, historical emissions data, toxicological reference values, and current regulatory guidance. Chronic inhalation exposure scenarios were evaluated using established risk assessment methodologies while considering both facility-related emissions and representative background concentrations. Combining environmental engineering, atmospheric science, industrial process evaluation, exposure science, epidemiology, and toxicology produced a comprehensive environmental forensic evaluation capable of supporting environmental consulting, regulatory investigations, environmental due diligence, remediation planning, and expert witness services involving complex airborne hazardous air pollutants (National Academies of Sciences, Engineering, and Medicine, 2022; U.S. EPA, 1989).
Results
The environmental forensic investigation demonstrated that historical ethylene oxide (EtO) emissions varied substantially over time because of changes in industrial production, process modifications, emission control technologies, and facility operations. Reconstruction of historical emissions inventories showed that numerous industrial sources contributed to regional EtO emissions during different operational periods, with annual emissions fluctuating significantly as manufacturing practices evolved. Evaluating these long-term trends was essential for accurately characterizing historical community exposure because emissions from individual facilities changed considerably over multiple decades rather than remaining constant. Integrating historical emissions inventories with engineering evaluations provided a scientifically robust foundation for reconstructing representative historical emission scenarios and estimating long-term ambient EtO concentrations (U.S. EPA, 2024; U.S. EPA, 2017).
Atmospheric dispersion modeling demonstrated that prevailing meteorological conditions exerted a dominant influence on the transport and distribution of EtO following release. Wind direction, atmospheric stability, mixing height, terrain, and source characteristics collectively influenced predicted ambient concentrations throughout the surrounding area. Modeling results indicated that ambient EtO concentrations varied spatially and temporally in response to changing meteorological conditions and source emissions rather than remaining uniformly distributed. Geographic information system analyses further illustrated regional concentration gradients and allowed modeled concentrations to be compared with available environmental monitoring information, strengthening confidence in the overall conceptual exposure model (American Meteorological Society & U.S. EPA, 2019; U.S. EPA, 2017).
Evaluation of ambient air monitoring data demonstrated both the value and limitations of direct environmental measurements for assessing long-term EtO exposure. Monitoring results confirmed that measurable EtO concentrations could be detected throughout the study area, including at locations without known nearby industrial emission sources. The occurrence of measurable background concentrations highlighted the importance of distinguishing regional ambient EtO from facility-specific contributions during environmental forensic investigations. The investigation further demonstrated that many measured concentrations approached analytical detection limits, increasing uncertainty associated with individual sampling events. Consequently, environmental monitoring was interpreted together with engineering analyses and atmospheric dispersion modeling rather than independently, providing a more scientifically defensible assessment of long-term community exposure (U.S. EPA, 2024; Kirman & Hays, 2017).
Comparison of modeled and monitored concentrations demonstrated general consistency between predicted ambient concentrations and observed environmental measurements while also illustrating the inherent variability associated with low-level atmospheric monitoring. The investigation found that air dispersion modeling provided a more reliable method for estimating long-term average community exposure than short-duration monitoring events alone because atmospheric models integrate historical emissions, source characteristics, and meteorological conditions over extended periods. This integrated approach reduced uncertainty associated with temporal fluctuations and analytical limitations while providing a scientifically sound framework for evaluating historical environmental conditions (American Meteorological Society & U.S. EPA, 2019; U.S. EPA, 2017).
Overall, the investigation demonstrated that combining historical emissions reconstruction, engineering evaluations, atmospheric dispersion modeling, ambient air monitoring, environmental chemistry, toxicology, and quantitative exposure assessment produced a comprehensive environmental forensic evaluation of historical EtO emissions. No individual dataset independently characterized long-term community exposure; however, integrating multiple independent lines of evidence substantially strengthened source attribution, improved interpretation of environmental monitoring data, and provided a technically rigorous basis for environmental consulting, regulatory investigations, environmental due diligence, remediation planning, and expert witness services involving airborne hazardous air pollutants (ASTM International, 2021; National Academies of Sciences, Engineering, and Medicine, 2022).
Conclusions
This environmental forensic investigation demonstrated that evaluating historical ethylene oxide (EtO) emissions requires a comprehensive multidisciplinary approach integrating environmental engineering, atmospheric science, industrial process evaluation, environmental chemistry, epidemiology, toxicology, air dispersion modeling, exposure assessment, and quantitative risk assessment. Because ambient EtO concentrations are influenced by multiple industrial sources, regional background concentrations, meteorological variability, and evolving industrial operations, accurately reconstructing historical community exposure requires the integration of multiple independent scientific disciplines rather than reliance upon any single dataset. The weight-of-evidence approach employed in this investigation provided a scientifically robust framework for evaluating historical emissions while improving confidence in the interpretation of environmental monitoring and modeled air concentrations (ASTM International, 2021; U.S. EPA, 2017).
The investigation demonstrated that historical emissions inventories and engineering analyses are fundamental components of environmental forensic evaluations involving airborne hazardous air pollutants. Industrial emissions changed substantially over time as manufacturing practices, production rates, pollution control technologies, and regulatory requirements evolved. Reconstructing these historical operating conditions allowed representative source terms to be developed for atmospheric dispersion modeling, providing a more scientifically realistic estimate of long-term ambient concentrations than would be possible using contemporary emissions data alone. This historical perspective is essential when evaluating potential chronic exposures associated with industrial operations spanning multiple decades (U.S. EPA, 2024; American Meteorological Society & U.S. EPA, 2019).
The investigation further demonstrated the importance of integrating ambient air monitoring with atmospheric dispersion modeling when evaluating low-concentration airborne contaminants such as EtO. While environmental monitoring provides valuable empirical information, measurements approaching analytical detection limits may be influenced by method sensitivity, temporal variability, and naturally occurring or regional background concentrations. Air dispersion modeling complements monitoring by integrating source characteristics, emissions, and meteorological conditions over extended periods, thereby providing a more comprehensive understanding of long-term community exposure. Evaluating these independent lines of evidence collectively strengthens source attribution and reduces uncertainty associated with individual measurements or isolated sampling events (Kirman & Hays, 2017; U.S. EPA, 2017).
This case study highlights the critical role of environmental forensic science in evaluating historical industrial emissions involving hazardous air pollutants and complex community exposure scenarios. By integrating historical emissions reconstruction, industrial process engineering, atmospheric dispersion modeling, meteorological analysis, environmental chemistry, toxicology, epidemiology, exposure science, and quantitative human health risk assessment, RoseyFields provides scientifically rigorous evaluations capable of supporting environmental consulting, regulatory investigations, environmental due diligence, remediation planning, and expert witness services. These multidisciplinary investigations provide objective, evidence-based scientific analyses that improve understanding of historical emissions, atmospheric transport, environmental exposure, and potential human health risks while remaining consistent with accepted engineering practice, current environmental science, and evolving regulatory guidance (National Academies of Sciences, Engineering, and Medicine, 2022; U.S. EPA, 2016).
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, hazardous air pollutant exposure assessment, historical emissions reconstruction, air dispersion modeling, and human health risk evaluation. Dr. Rosenfeld’s work focuses on complex environmental contamination matters involving ethylene oxide emissions, industrial sterilization and chemical manufacturing operations, cumulative multi-source air impacts, atmospheric transport, background-versus-facility source attribution, ambient air monitoring interpretation, and long-term community exposure pathways affecting residential populations near industrial corridors. His expertise includes reconstructing historical emission scenarios through the integration of emissions inventories, industrial process engineering, meteorology, environmental chemistry, toxicology, epidemiology, air dispersion modeling, and quantitative exposure assessment to determine whether historical industrial operations are consistent with observed environmental conditions and potential human health impacts. 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, industrial air emissions, chronic inhalation exposure, source attribution, and long-term environmental and human health risks associated with hazardous air pollutants.
References
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Kirman, C. R., & Hays, S. M. (2017). Ethylene oxide exposure, endogenous production, and risk assessment: A review of key issues. Critical Reviews in Toxicology, 47(8), 709–730.
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