Recommended Default Methodology for Analysis of Airborne Exposures to Mixtures of Chemicals in Emergencies

Abstract

Emergency planning and hazard assessment of Department of Energy (DOE) facilities require consideration of potential exposures to mixtures of chemicals released to the atmosphere. Exposure to chemical mixtures may lead to additive, synergistic, or antagonistic health effects. In the past, the consequences of exposures to each chemical have been analyzed separately. This approach may not adequately protect the health of persons exposed to mixtures. This article presents default recommendations for use in emergency management and safety analysis within the DOE complex where potential exists for releases of mixtures of chemicals. These recommendations were developed by the DOE Subcommittee on Consequence Assessment and Protective Actions (SCAPA). It is recommended that hazard indices (e.g., HIi = Ci/Limiti, where Ci is the concentration of chemical "i") be calculated for each chemical, and unless sufficient toxicological knowledge is available to indicate otherwise, that they be summed, that is, sigma i(n) = 1HIi = HI1 + HI2 + ... + HIn. A sum of 1.0 or less means the limits have not been exceeded. To facilitate application of these recommendations for analysis of exposures to specific mixtures, chemicals are classified according to their toxic consequences. This is done using health code numbers describing toxic effects by target organ for each chemical. This methodology has been applied to several potential releases of chemicals to compare the resulting hazard indices of a chemical mixture with those obtained when each chemical is treated independently. The methodology used and results obtained from analysis of one mixture are presented in this article. This article also demonstrates how health code numbers can be used to sum hazard indices only for those chemicals that have the same toxic consequence.

The Toxicology of Chemical Mixtures Risk Assessment for Human and Ecological Receptors

“…The approach assumes that for two chemicals, when the mode of action is not the same, interaction does not occur (Craig et at., 1999) or interaction will be insignificant at environmental exposure levels (U.S. EPA, 2000). A good dose-response curve for each component is necessary for calculating response addition; the data, cancer or non-cancer, should be expressed as percent responding (Teuschler et al, 2001).…”

“…The procedure is also used by the ACGIH and the Occupational Safety and Health Administration (OSHA) (ATSDR, 2001a). The 24 Department of Energy (DOE) calculates emergency airborne exposures by the HI procedure (Craig et al, 1999).…”

“…ACGIH and OSHA divide the eight-hour time weighted average exposure concentration for individual chemicals by the chemical's threshold limit value (TLV) or permissible exposure level (PEL) to derive their HQs, respectively (ATSDR, 2001a). For emergency planning purposes, the DoE recommends dividing the maximum expected airborne concentration of each component by its temporary emergency exposure limit (TEEL) (Craig et al, 1999). The HI approach attempts to approximate the toxicity of the mixture if the mixture were to be tested in entirety (U.S. EPA, 2000).…”

“…The U.S. Army Center for Health Promotion and Preventative Medicine (USACHPPM) is developing a hierarchical chart of 14 target systems (e.g., skeletal, nervous) divided into 76 target organs (e.g., bone, ligaments and cartilage, connective tissue) to help guide placement of chemical found at a site into the appropriate HI calculations (Johnson, personal communication, 2004). Similarly, the DoE uses health code numbers such as those published in Patty's Industrial Hygiene and Toxicology (John Wiley and Sons, NY) to sort chemicals by target organ and mode of action (Craig et al, 1999).…”

Health hazard evaluation report: HETA-2000-0134-2847, SFO International Terminal, San Francisco, California.

“…If the units for the exposure limits are different (e.g., mg/m³ versus 'fibers per cc'), then the 'unity formula' approach discussed by the ACGIH is appropriate. Additional guidance regarding dealing with exposures to mixtures can be found in the following references: Ballantyne (1985), Krystofiak and Schaper (1996), and Craig et al (1999).…”