The development of acute exposure guideline levels for hazardous substances
ABSTRACT The primary purpose of the National Advisory Committee for Acute Exposure Guideline Levels for Hazardous Substances (NAC/AEGL) is to develop guideline levels for short-term exposures to airborne concentrations for approximately 400 to 500 high priority, acutely hazardous substances within the next ten years. These Acute Exposure Guideline Levels (AEGLs) are needed for a wide range of planning, response, and prevention applications.
The NAC/AEGL Committee seeks to develop the most scientifically credible, acute (short-term) exposure guideline levels possible within the constraints of data availability, resources and time. This includes a comprehensive effort in data gathering, data evaluation and data summarization; fostering the participation of a large cross-section of the relevant scientific community; and the adoption of procedures and methods that facilitate consensus-building for AEGL values within the Committee. The NAC/AEGL Committee is currently comprised of representatives of federal, state and local agencies, private industry and other organizations in the private sector that will derive programmatic or operational benefits from the existence of the AEGL values.
AEGL values are determined for three different health effect end-points. These values are intended for the general public where they are applicable to emergency (accidental) situations. Threshold exposure values are developed for a minimum of 4 exposure periods (30 minutes, 1 hour, 4 hours, 8 hours). In certain instances, AEGL values for a 10-minute exposure period also will be developed. Each threshold value is distinguished by varying degrees of severity of toxic effects, as initially conceived by the AIHA ERP Committee, subsequently defined in the NAS' National Research Council Report, Guidelines for Developing Community Emergency Exposure Levels for Hazardous Substances, published by the National Academy of Sciences in 1993, and further refined by the NAC/AEGL Committee. To date, the committee has reviewed over 80 chemicals.
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ABSTRACT: Emergency preparedness personnel at U. S. 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) for each chemical in a mixture 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 exceeding the concentration limit and indicates the potential for adverse health effects. Next, Health Code Numbers (HCNs) are used to identify the target organ systems that may be impacted by exposure to each chemical in a mixture. The sum of the HIs for the maximally impacted target organ system 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 enhance the effectiveness of the CMM by using HCN weighting factors. 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 weighting factors that are based on the exposure route used to derive PAC values and a priority ranking of the HCNs (the same ranking as used in the second approach). Initial testing indicates that applying weighting factors increases the effectiveness of the CMM chemical mixtures in general, though care must be taken to avoid introducing non-conservative results. In the near future, additional testing and analysis will be conducted that may lead to the adoption of one of the tested approaches into the CMM.Toxicology 11/2012; 313(2-3). DOI:10.1016/j.tox.2012.10.011 · 3.75 Impact Factor
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ABSTRACT: The primary aim of the Acute Exposure Guideline Level (AEGL) program is to develop scientifically credible limits for once-in-a-lifetime or rare acute inhalation exposures to high-priority, hazardous chemicals. The program was developed because of the need of communities for information on hazardous chemicals to assist in emergency planning, notification, and response, as well as the training of emergency response personnel. AEGLs are applicable to the general population, including children, the elderly, and other potentially susceptible subpopulations. AEGLs are the airborne concentrations of chemicals above which a person could experience notable discomfort or irritation (AEGL-1); serious, long-lasting health effects (AEGL-2); and life-threatening effects or death (AEGL-3). AEGLs are determined for five exposure periods (10 and 30 min and 1, 4, and 8 h). Physiologically based pharmacokinetic (PBPK) models can be very useful in the interspecies and time scaling often required here. PBPK models are used for the current article to predict AEGLs for trichlorethylene (TCE), based on the time course of TCE in the blood and/or brain of rats and humans. These AEGLs are compared to values obtained by standard time-scaling methods. Comprehensive toxicity assessment documents for each chemical under consideration are prepared by the National Advisory Committee for AEGLs, a panel comprised of representatives of federal, state, and local governmental agencies, as well as industry and private-sector organizations. The documents are developed according to National Research Council (NRC) guidelines and must be reviewed by the NRC Subcommittee on Acute Exposure Guideline Levels before becoming final. AEGLs for 18 chemicals have been published, and it is anticipated that 40 to 50 chemicals will be evaluated annually.Journal of Toxicology and Environmental Health Part A 04/2004; 67(8-10):621-34. DOI:10.1080/15287390490428017 · 1.83 Impact Factor
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ABSTRACT: Risk assessment utilizes human and animal studies and mathematical models to arrive at threshold exposures for toxic effects of various chemicals. In 1995 the Environmental Protection Agency (EPA) formed an acute risk assessment committee to assist in the planning for worst case chemical releases. The National Advisory Committee for Acute Exposure Guideline Levels (AEGL) examines the toxicological properties and studies of each chemical and then recommends appropriate levels. For the majority of chemicals, the committee relies on animal data (where the most data exists) supplemented with a limited number of human studies. In some cases, human studies are relied on to derive AEGL values. In the published levels for hydrogen cyanide (HCN), the AEGL committee used five human studies and a "weight-of-the-evidence" approach. A number of these studies did not investigate adverse health effects, however, the AEGL committee used these studies as evidence that no health effect occurred. In addition, a number of other errors in conflict with well accepted principles of industrial hygiene were made. In order to adequately evaluate human studies, risk assessment committees must be composed of a balance of professionals with a wide variety of expertise, including epidemiology and industrial hygiene.American Journal of Industrial Medicine 04/2005; 47(4):370-5. DOI:10.1002/ajim.20142 · 1.59 Impact Factor