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5 Process for Establishing and Applying Military Exposure Guidelines The health-protective nature of the current military exposure guidelines (MEGs) makes them most appropriate for use as part of the Army’s force health protection initiative. In this chapter, the subcommittee reviews how MEGs were derived in Reference Document 230 (RD-230) (USACHPPM 2002) and provides comments and recommendations on their application. In addition, the subcommittee considers the need to address risks from multiple exposure pathways, multiple chemicals, and repeated deployments. AIR EXPOSURE GUIDELINES This section provides a summary of the U.S. Army Center for Health Promotion and Preventive Medicine’s (USACHPPM’s) approaches to de- riving its current air MEGs. The basic approach to determining air MEGs was to review the exposure guidelines of other agencies, use a hierarchical scheme to select the most appropriate guideline for the exposure duration of interest, and then adjust that guideline to meet the military’s needs, if necessary. Air MEGs were developed for exposures of 1 hour, 8 hours, 14 days, and 1 year. In the sections below, the process used to derive the duration-specific MEGs is described and evaluated, followed by a review of some chemical-specific MEGs and criteria air pollutants. 91
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92 TECHNICAL GUIDES ON ASSESSING AND MANAGING CHEMICAL HAZARDS 1-Hour MEGs Derivation One-hour air MEGs were developed to consider three levels of health effects: • Minimal effects. Above this level, individuals could begin to experience mild, transient effects that should not impair performance. • Significant effects. Above this level, individuals could begin to experience irreversible or serious effects that might degrade performance and incapacitate a small portion of the people exposed. • Severe effects. Above this level, some within an exposed popula- tion could begin to experience life-threatening or lethal effects. The hierarchy used to select source material was (1) acute exposure guide- line levels (AEGLs), (2) emergency response planning guidelines (ERPGs), (3) temporary emergency exposure limits (TEELs), and (4) other. AEGLs are developed by the U.S. Environmental Protection Agency (EPA) and reviewed by a National Advisory Committee and by the National Research Council (NRC). AEGLs are developed for three severity levels, and all of the values are intended to protect the general public, including sensitive and susceptible subpopulations. Above AEGL-1 concentrations, the general population could experience discomfort and irritation effects that are not disabling and are reversible upon cessation of exposure. Above AEGL-2 concentrations, the general population could experience irrevers- ible or serious health effects or impaired ability to escape. Above AEGL-3, the general population could experience life-threatening health effects or death. These levels were developed for exposure durations of 10 minutes (min), 30 min, 1 hour, 4 hours, and 8 hours. All AEGL-1 and AEGL-2 exposures were reviewed by EPA to ensure that they do not pose an excess cancer risk greater than 1 × 10-4. ERPGs are developed by the American Industrial Hygiene Association (AIHA) and are intended for emergency planning and response operations. They also have three levels of health effects that are quite similar to those of the AEGLs. They were created to target the general population, but not particularly susceptible individuals. TEELs are developed by the U.S. Department of Energy and are essentially interim ERPGs.
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MILITARY EXPOSURE GUIDELINES 93 Evaluation The hierarchy for selecting sources for the 1-hour MEGs is based on a logical argument and is consistent with the NRC (2000) recommendations for developing standards. The NRC (2000) noted that in the development of guidelines, different kinds of guidelines are appropriate for different settings. The report also stated that it is useful to allow for guidelines that permit some degree of toxic response but protect against incapacitation or irreversible injury for use in decision making during emergencies or when important risk trade-off decisions must be made quickly, such as in combat. The quality of the 1-hour MEGs is limited to the quality of the source assessments. Those assessments are, in turn, limited by the quality of the database and how recently the assessments were performed. AEGLs can be assumed to be of higher quality because they were developed recently, had more data to consider, and are extensively peer-reviewed. However, they are few in number. That makes it important for TG-230 and RD-230 to be “living” documents that incorporate new values as soon as they become available. For example, RD-230 mentions that interim and proposed AEGLs were used. It is necessary to track the final versions and to ensure that the final AEGL values are incorporated into the documents. As chemicals are selected for AEGLs development, USACHPPM should give priority consid- eration to those chemicals likely to be found in major theaters of operations. The 1-hour air MEGs are based on different sources. To facilitate making updates, it would be useful to document the existing guideline used and the date it was established in the supporting reference tables. In addi- tion, the entries in air MEG tables provided in TG-230 should be reviewed to ensure that they describe specific end points of interest. Currently, some entries in the tables provide only a broad description of the critical-study end points (e.g., systemic, irritation). Sometimes the entries do not describe the end points at all (e.g., “based on a slightly higher incidence of nasal tumors in rats,” “based on extrapolation of acute animal data and limited evidence in humans”). 8-Hour Air MEGs Derivation RD-230 indicates that the exposure duration of 8 hours was selected to
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94 TECHNICAL GUIDES ON ASSESSING AND MANAGING CHEMICAL HAZARDS be consistent with brief exposures. The corresponding MEGs represent levels below which no significant adverse health effects are expected and above which the probability of adverse health effects is increased. The 8- hour MEGs incorporate the assumption that exposures will be continuous. The hierarchy used to select sources to establish the 8-hour MEGs was (1) AEGL-1 values and (2) Threshold Limit Values (TLVs), which are devel- oped by the American Conference of Governmental Industrial Hygienists (ACGIH). The TLVs are developed to protect workers against the effects of a working lifetime of exposure (8 hours/day, 5 days/week, and 50 weeks/year for a working lifetime). RD-230 used the TLVs for 8-hour exposures when no AEGLs were available. In a number of cases, the 8- hour air MEGs are the same as the 1-hour air MEGs for minimal effects. Evaluation Because relatively few 8-hour AEGLs have been derived, TLVs are the preferred sources for the 8-hour MEGs. ACGIH criticizes the direct use of TLVs for purposes other than those intended. However, feasible alterna- tives will not exist until more AEGLs are established. TLVs are concentra- tions expected to be relatively safe for worker populations exposed intermit- tently (8-hour workdays) for a working lifetime. Thus, their direct applica- tion to a single 8-hour period is likely to be protective. Whether that ap- proach is overly protective depends on the database and the calculations that were used to set the particular TLV. TLVs do not use standardized formu- las, so it would be difficult to determine the likely margins of conservatism that were used to establish them. Determining what modifications are nec- essary to create an 8-hour MEG for continuous exposure from a TLV de- signed to be protective for intermittent exposure over a working lifetime is even more difficult. But, until revisions can be made, this approach is the most feasible, however overprotective. It appears that no consideration was given to making adjustments for the higher inhalation rate of deployed personnel; it might be appropriate to make those adjustments for 8-hour exposures. In the future, it would be useful to examine the data underlying the values selected for MEGs to determine whether the original data in- cluded exposure durations closer to 8 hours and therefore might be more appropriate than the calculations used by other agencies for other purposes.
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MILITARY EXPOSURE GUIDELINES 95 14-Day MEGs Derivation The 14-day air MEGs incorporate the assumption that exposures will be continuous, recognizing the limited likelihood of that in the real world and that simplifications are essential to create workable guidelines. The hierarchy for selecting the sources of the 14-day MEGs was (1) continuous exposure guidance levels (CEGLs), (2) minimal risk levels (MRLs), (3) TLVs, and (4) special considerations. CEGLs were developed by the NRC (1986) for exposures to military personnel lasting up to 90 days. They are intended to prevent serious or permanent effects in a healthy male popula- tion and do not include consideration of susceptible subpopulations. The 14-day MEGs consider the possibility that increasing concentration or duration could increase the potential for delayed or permanent disease (e.g., kidney disease or cancer). MRLs are developed by the Agency for Toxic Substances and Disease Registry (ATSDR) for noncancer effects. An MRL is an estimate of the daily human exposure to a hazardous substance that is likely to be without appreciable risk of adverse health effects over a specified duration of expo- sure. These estimates are intended to serve as screening levels to identify contaminants and potential health effects that might be of concern at haz- ardous waste sites. ATSDR creates MRLs for acute (1-14 days), intermedi- ate (14-364 days), and chronic (365 days or longer) exposures. Although RD-230 states that the TLVs were not considered protective for continuous exposures of over 24 hours to 14 days, the TLVs were ex- trapolated down from working lifetime values to 14-day continuous expo- sure values. TLVs for “systemic” or “mixed-acting” substances were ad- justed by a factor of 5 days/7 days, a ventilation factor of 10 m3/20 m3 (10m3 is the worker 8-hour default factor) with another calculation of 20 m3/29.2 m3 to account for the military person’s increased ventilation rate (see Chapter 3) (equaling 10 m3/29.2 m3) , and an uncertainty factor of 10 to account for the uncertainty of extrapolation from intermittent to continu- ous exposure (see Equation 5-1). 14-day MEG = (TLV × 5 days/7 days × 10 m3/29.2 m3) × 0.1 (5-1) The TLVs for irritants were not adjusted because they are assumed to be mostly concentration-dependent.
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96 TECHNICAL GUIDES ON ASSESSING AND MANAGING CHEMICAL HAZARDS USACHPPM determined that more than 24 hours of continuous expo- sure to chemical warfare agents (CWAs) is unlikely. Therefore, no MEGs were established for CWAs for periods greater than 1 day. Twenty-four- hour MEGs for CWAs were derived by linear extrapolation from the 8-hour MEGs. Evaluation The CEGLs were derived assuming 90 days of continuous exposure, so it is likely that they are conservative. Because many were published in the late 1980s, some of them could be out-of-date. Furthermore, CEGLs were developed for use by the Navy on submarines and, therefore, the target population was assumed to be exclusively male. Thus, female reproductive end points and developmental toxicity were not considered in setting the CEGLs. The acute MRLs were calculated on the basis of exposure durations of 1-14 days. Thus, they are reasonably targeted for duration; however, they include UFs for susceptible groups. The MRL-based calculations for MEGs do not appear to include adjustments for military ventilation rates. USACHPPM should make those adjustments. For the 14-day values based on TLVs, adjusting the TLVs for the change from 8 hour/day, 5 day/week to 24 hour/day, 7 day/week and for the higher breathing rates of military personnel (i.e., 14-day air MEGs = TLVs × 5 days/7 days × 10 m3/29.2 m3) is reasonable for systemic chemicals when dose rate is not the determining factor and only total dose dictates effects (Gaylor 2000). The calculations assume that a C (concentration) × t (time) = k (total exposure) relationship holds for systemic effects. The basis for the 29.2 m3/day ventilation rate is reasonable, although it contains several assumptions. Because TLVs are intended to be protective over a worker’s lifetime, extrapolating 14-day continuous exposures from 8-hour TLVs introduces significant uncertainty. A UF of 10 was used to extrapolate from intermit- tent to continuous exposure. EPA and ATSDR make similar extrapolations for RfCs and MRLs, respectively, but do not use a UF. A weak justification is offered in RD-230, which says that some health effects have been ob- served in some workers at the TLV levels, without further specification. However, the UF of 10 is unduly conservative. Typically, concentration is more important than duration in the C × t equation (beyond acute lethality). When a guideline for intermittent exposure is converted to one for continu- ous exposure, it becomes more conservative. For example, consider an
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MILITARY EXPOSURE GUIDELINES 97 intermittent TLV of 0.5 mg/m3 for 8 hour/day, 5 days/week for 260 days/ year, or 2,080 hours of exposure. That is equivalent to a total exposure (k) of 1,040 mg-h/m3. When that value is converted to a continuous exposure (24 hours/day for 365 days, or 6,360 hours), the comparable C would be 0.16 mg/m3 (i.e., C = k ÷ t). In other words, if C × t = k operates, an inter- mittent inhalation of 0.5 mg/m3 is equivalent to a continuous inhalation of 0.16 mg/m3. Therefore, the 0.16 mg/m3 has built-in conservatism that is appropriate. Applying an additional UF of 10 would result in a guideline of 0.016 mg/m3, which is overly conservative. The 14-day air MEGs are difficult to develop because most of the source materials have different exposure durations and use different assess- ment methodologies. Table 5-1 summarizes the sources and highlights the differences in the portions of lifetime protected and the adjustments that were made to the source material. It would be advisable to check the refer- ence data of the sources to determine to what degree the databases were founded on studies approximating the duration of military interest. If ap- propriate, other data might be used to derive MEGs. Also, it would be best to use a standard approach to applying adjustments across all values. For example, adjustments for military ventilation rates should be used in all the MEGs. 1-Year Air MEGs Derivation The one-year air MEG is defined by USACHPPM (2002) as “The air- borne concentration for a continuous exposure up to 1 year (365 days, 24 TABLE 5-1 Sources for 14-day Air MEGs Exposure Source Duration and Portion of Lifetime USACHPPM Adjustments in Reference Frequency Protected 14-Day Air MEGs CEGL 90 days, 90 days No adjustments were made continuous MRL 1-14 days, daily 1-14 days No duration or ventilation rate adjustments were made TLVs 8 hours/day, 5 Working lifetime Adjustments to continuous days/ week 14-day and military ventilation rates
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98 TECHNICAL GUIDES ON ASSESSING AND MANAGING CHEMICAL HAZARDS hours/day) that is considered protective against all health effects including chronic disease and increased risk to cancer (i.e., cancer risk greater than 1 × 10-4). No performance degradation or long-term health consequences are expected with exposure at or below this level. Increasing concentration and/or duration could increase the potential for delayed/permanent disease (e.g., kidney disease or cancer).” The 1-year MEGs were not designed to address continuous exposure exceeding 1 year. Inhalation reference concentrations (RfCs) for noncarcinogenic effects, air unit risks, or inhalation cancer slope factors (CSFi) from the EPA’s Integrated Risk Information System (IRIS) and the Health Effects Assess- ment Summary Tables (HEAST) were selected to derive preliminary long- term MEGs (PMEG-L). When those EPA sources were not available, addi- tional sources, including TLVs and MRLs, were used with additional ad- justments (see discussion below). For carcinogenic polycyclic aromatic hydrocarbons (PAHs), provisional EPA values were used; they included toxicity equivalence factors relative to benzo(a)pyrene. The air-MEG selec- tion was based on the following hierarchy: (1) PMEG-L, (2) TLV-adjusted, and (3) MRL-adjusted. If significant (more than an order of magnitude) discrepancies between those values existed, USACHPPM reviewed the data and selected the final 1-year air MEGs. Derivation of PMEG-Ls USACHPPM developed military “noncancer” risk concentrations (MRCs) and cancer risk concentrations (MCRCs) using a method similar to that used in the derivation of EPA’s Region III risk-based concentration values, which are consistent with risk-assessment guidance for Superfund. The cancer and noncancer values were compared, and the lower one (i.e., the more protective one) was identified as the PMEG-L. Because a 1-year exposure duration is of interest for noncancer risks, the first-choice sources were the subchronic RfCs in HEAST; if those were not available, chronic values were used. Subchronic is defined as one-tenth of the average lifespan, or 2 weeks to 7 years, and chronic is defined as more than 7 years. To derive MRCs, RfCs (in units of milligrams per cubic meter [mg/m3]) were converted to reference doses (RfDs, in milligrams per kilogram per day [mg/kg/day]) by multiplying the inhalation rate of 20 m3/day and dividing by 70 kg, the average weight for adults. With the target hazard quotient (THQ) set at 1, a backward calculation was per- formed to derive the MRCs using the following assumptions: (1) body weight (BW) of 70 kg, (2) military inhalation rate (IRA) of 29.2 m3/day, (3)
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MILITARY EXPOSURE GUIDELINES 99 exposure duration (ED) of 1 year, (4) exposure frequency (EF) of 365 days/year, and (5) average time (AT) of 365 days (see Equation 5-2). THQ × RfD × BW × AT MRC = (5-2) EF × ED × IRA EPA’s CSFs were used as a basis for deriving the MCRCs. Those unit cancer risks also were converted from risk per microgram per cubic meter to risk per milligram per kilogram per day, assuming a body weight of 70 kg and an inhalation rate of 20 m3/day. To calculate the MCRC, the target cancer risk (TCR) was set at 1 × 10-4 and the following assumptions were made: (1) BW = 70 kg, (2) IRA = 29.2 m3/day, (3) ED = 1 year, (4) EF = 365 days/year, and (5) AT = 25,550 days (70 years × 365 days) (see Equa- tion 5-3). TCR × BW × AT MCRC = (5-3) EF × ED × IRA × CSF Adjustments of TLVs and MRLs When TLVs were used as the sources for the 1-year MEGs, they were adjusted to account for the military person’s assumed respiratory rate and for uncertainties associated with extrapolating values for intermittent expo- sures to continuous exposures. For extrapolation, a UF of 10 was applied. However, the TLVs for irritants were not duration-adjusted. Intermediate MRLs (15-364 days) were given preference over chronic MRLs. The MRLs were adjusted to account for the assumed military inha- lation rate. Evaluation Quality of the Source References EPA, ACGIH, and ATSDR sources are appropriate. IRIS is the only fully official set of EPA assessments. HEAST includes some values that have not been agreed on, some that have not been peer-reviewed, and some that have been removed from IRIS because of quality problems. Also, the
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100 TECHNICAL GUIDES FOR ASSESSING AND MANAGING CHEMICAL HAZARDS use of provisional values for PAHs that are close to 10 years old suggests that some significant uncertainties in the available data have not been ad- dressed. Furthermore, many of the current IRIS values, TLVs, and MRLs are out-of-date, and some of them are obsolete because of newer informa- tion. Although it is not feasible for DOD to revise all the source data, po- tential problems associated with using those sources should be recognized and stated. EPA Region IX values were used as sources for many of the 1-year MEGs; however, those EPA values were created using a complex process and they have little apparent worth for the MEGs. The rationale offered by USACHPPM for the MRC and MCRC adjustments from milligrams per cubic meter to milligrams per kilogram per day appears to be numerically driven, and ultimately the additional conversion factors cancel themselves out. That conversion, however, was not applied to MRLs and TLVs. In developing the RfC and cancer unit risks, EPA made decisions to use milli- grams per cubic meter or micrograms per cubic meter as the units for the durations of interest (typically continuous exposure for 70 years). Those units are used in the underlying research studies and are the units that would eventually be used in regulations. Although cubic meters of air breathed per day has a relationship to body weight, the convention of measuring exposure in milligrams per cubic meter is more accurate than the milligrams per kilogram per day. Conversion from an RfC or a cancer unit risk to milligrams per kilogram per day at the level of the individual studies would introduce unnecessary uncertainties. The subcommittee recommends that USACHPPM consult additional sources of guideline values, such as the World Health Organization (WHO 2001) and the State of California. WHO (2001) has health-based guidelines for 35 air pollutants, and most were derived using expert judgment and include consideration of susceptible populations. The State of California has hundreds of values that were derived following a standard procedure similar, but not identical to that used by EPA. The subcommittee recommends that HEAST values not be used to derive long-term air MEGs, because the quality of those assessments is not as strong as that of the other guidelines. For the other sources, the date of the original assessment should be provided in the tables in RD-230 to indi- cate the degree of potential obsolescence of the source material. Inhalation Adjustment Factor Most of the starting values were adjusted from EPA, ACGIH, or MRL
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MILITARY EXPOSURE GUIDELINES 101 ventilation defaults of 20 m3/day or 10 m3/day to the military ventilation rate of 29.2 m3/day. The military default rate is based on a series of mea- surements, scenario estimations, and judgments. No default rate is or will ever be perfect, so the rate should be judged relative to its purpose of pro- viding an appropriate level of protection for the population of concern. USACHPPM evaluated all the components of the military inhalation rate assumption, and on the basis of limited information for the types of activity likely to be performed, concluded that it is reasonable (see Chapter 3). However, the RfC methodology used to derive several of the MEGs in- cludes a dosimetric extrapolation from animals to humans that considers ventilation rate. The implications of that are likely to be greater for reactive gases and some particles. The dosimetric model is based on a ventilation rate of 20 m3/day, and a rate of 29.2 m3/day would alter the pattern of respi- ratory tract deposition. RfCs are based on regional deposited dose when that method is supported by the data. Thus, ventilation can influence the RfC, depending on the specific circumstances. For example, a reactive gas with an assessment based on nasopharyngeal doses might be impacted. That possible impact is unlikely to have a major influence on the MEGs, but it bears consideration if there is an attempt to go back to the original data and recalculate the MEGs. Applying a UF of 10 to the TLVs Extrapolating the TLVs from intermittent to continuous exposures is acceptable for nonirritants because incorporating the area under the expo- sure curve is scientifically appropriate and is routine practice in most as- sessments (e.g., RfC, MRLs). However, applying a UF of 10 is not support- able, as discussed earlier (see “14-Day Air MEGs”). The MEGs should therefore be revised. Varying Exposure Durations One overarching problem is that the 1-year air MEGs are based on source references with varying exposure durations. Table 5-2 summarizes the exposure durations and frequencies associated with the sources used by USACHPPM in developing the 1-year air MEGs. USACHPPM mentioned that they used subchronic RfCs when they are available. However, the chronic RfCs and unit cancer risks, which are both based on lifetime exposure, were also used. For carcinogenic agents, the MCRCs are derived by averaging the 70-year cumulative lifetime dose limit
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120 TECHNICAL GUIDES FOR ASSESSING AND MANAGING CHEMICAL HAZARDS develop appropriate risk-management plans for when measured or predicted exposure concentrations exceed the MEGs and how to adequately character- ize the risks in the event of exposures to the same toxic agent through multi- ple routes and pathways or simultaneous exposures to several chemicals. Interpreting MEG Exceedances As noted in Chapter 2, two separate sets of guidelines are necessary to appropriately assess chemical threats to the mission and chemical threats to force health. Under this new scheme, it would not be appropriate for the health-based MEGs to be used in conjunction with the military’s mission risk assessment matrix to evaluate mission risks, as is currently recom- mended in TG-230. Rather, the subcommittee envisions that MEGs will be used as guidelines to assess health risks and the potential risk-management options for reducing or eliminating those risks. That information would then be considered by decision makers in conjunction with mission-related risk assessments. For example, in cases where some level of health risk is accepted to complete the military objective, MEGs could be used to deter- mine the medical follow-up responsibilities of DOD. The subcommittee recommends that DOD develop a risk-management framework that focuses on action plans (i.e., responses) for when MEGs are exceeded. Actions plans should include, but should not be limited to the following elements: • Formulating better characterizations of exposures, including identi- fication of the sources and of the contributions from various contaminated media. (More extensive discussion on exposure assessment is provided in Chapter 3.) • Setting limitations on the lengths of deployments. • Identifying remedial options. • Identifying exposed individuals who are at greater risk for adverse effects, triggering one or more of the following actions: —Post-deployment follow-up with exposed individuals. —Identification of unusually susceptible individuals. —Limitations on multiple deployments. —Consideration of the possibilities of other exposures contributing to the same health outcomes. —Provision of long-term care.
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MILITARY EXPOSURE GUIDELINES 121 Assessing Aggregate Exposure As discussed in Chapter 3, aggregate exposure is total exposure to a single chemical by multiple pathways and routes. The paths that chemicals travel to reach the media through which individual exposures occur are referred to as exposure pathways. Most pathways are complex. For exam- ple, lead added to gasoline (medium 1) is emitted to the air (medium 2) when gasoline is burned. Some of the airborne lead is deposited in soil (medium 3), which is used for growing corn. Some of the lead in soil dis- solves in water (medium 4) and moves through the roots of the corn plant, accumulating in the kernels of corn (medium 5), and the corn is fed to dairy cattle, leading some of the lead to be excreted in cows’ milk (medium 6). In this scenario, milk is the medium through which humans are exposed to the lead. The lead passed through six media before it reached human be- ings. To make matters more complex, humans could have been exposed to lead at several other points along the pathway—for example, by breathing the air (medium 2) or coming into contact with the soil (medium 3). Expo- sure routes are the ways that chemicals can move into the body. They include inhalation, ingestion, skin absorption, absorption through the eyes, placental transfer from a pregnant woman to the fetus, and transfer from mother to child through breast-feeding. In many cases, contaminated media (air, soil, or water) can lead to several exposure routes. For example, hu- mans could be exposed to an organic solvent in tap water through drinking the contaminated water or through inhaling chemical vapors during warm showers. All of the exposure possibilities should be considered when as- sessing human health risks. During short-term missions and deployments, the route of exposure most likely to be of relevance to deployed personnel is inhalation. During longer-term deployments, deployed personnel might be exposed to low levels of common contaminants through various environmental media. In those longer-term scenarios, personnel could inhale contaminants in air that were volatilized from soil and/or water; ingest contaminated water; and/or experience dermal exposures from bathing or from direct contact with con- taminated soils. Assessing risk from each exposure route independently might indicate “low to moderate” risk categories; however, considering these potential exposures in aggregate could indicate more significant risks. EPA’s hazard index (HI) method is an example of a simple aggregate- exposure assessment framework that could be implemented by DOD. EPA defines the HI method as an aggregation of individual hazard quotients (HQs) for each route of exposure. The HQs are ratios of exposures to refer-
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122 TECHNICAL GUIDES FOR ASSESSING AND MANAGING CHEMICAL HAZARDS ence concentrations. For example, the HQ for inhalation is calculated as follows: HQinhalation = Exposure Concentration (mg/m3). (5-4) RfC (mg/m3) An oral RfD, a dermal RfD, and/or an inhalation RfC must be defined for each route of concern. HQs for each route of concern can then be aggre- gated into an HI. HIpathway = HQoral + HQdermal + HQinhalation. (5-5) Risk increases with increasing HQs and HIs. Generally, HQs or HIs of less than or equal to 1 are of little concern, whereas HQs or HIs of greater than 1 are of greater concern. This is a simple summary of the EPA procedure. EPA’s methodology for aggregate exposure (EPA 1999b, 2001b) should be consulted for more details. For the purpose of assessing aggregate expo- sures involving MEG chemicals, the subcommittee recommends DOD adapt EPA’s method for use with MEGs. For example, HQair, water, or soil = Exposure Concentration/MEG; (5-6) HI = HQair + HQwater + HQsoil. (5-7) Assessing Cumulative Risk TG-230 points out that because “certain contaminants may have similar adverse effects on the human body, it is necessary to consider the total sum of all similar effects” (USACHPPM 2000a). The document further indi- cates that in the preliminary threat analysis, when occupational and environ- mental health (OEH) hazards are identified and prioritized, the effects of exposures to the same or similar chemicals through different media should be considered additive. Algorithms have been adopted by federal agencies to address the problem of exposures to multiple chemicals; however, in RD- 230 USACHPPM states that those quantitative approaches are “not well- suited to the overall qualitative/ranking nature of the TG-230 deployment risk assessment approach” (USACHPPM 2002b, p. 5). The subcommittee agrees that conventional algorithms used to assess health risks from multi- ple chemicals are not useful for assessing mission risks. However, for the
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MILITARY EXPOSURE GUIDELINES 123 purposes of force health protection, those algorithms are appropriate for assessing cumulative risks to the deployed force. The most common proce- dure is discussed below. Cumulative exposures involve exposures to multiple chemicals. EPA defines cumulative risk as the likelihood of occurrence of an adverse health effect from exposure to multiple chemicals that have common modes of toxicity from all routes and pathways. The subcommittee agrees with the Army’s assumption that the toxicity of a mixture of chemicals that have similar modes of action will be equal to the sum of the weighted dose toxic- ities of the individual chemicals in the mixture. When assuming “addi- tivity,” the methods for combining component data described in EPA’s Supplementary Guidance for Conducting Health Risk Assessment of Chemi- cal Mixtures (EPA 2000) could be implemented. The primary method for component-based risk assessments of mixtures of chemicals with similar modes of action is the hazard index (HI), which is derived from dose addition. In the EPA guidance, dose addition is inter- preted as simple similar action where the component chemicals act as if they were dilutions or concentrations of each other, differing only in rela- tive toxicity. Dose additivity might not hold for all toxic effects, and the relative toxic potency between chemicals might differ for different types of toxicity or for toxicity by different routes. To reflect those differences, an HI usually is developed for each exposure route of interest and for a single specific toxic effect or for toxicity to a single target organ. A mixture could then be assessed using several HIs, each representing one route and one toxic effect or target organ. EPA’s HI is defined as a weighted sum of the exposure measures for the mixture component chemicals. According to dose addition, the “weight” factor should be a measure of the relative toxic strength. The guidelines formula for the HI is general. n HI1 = Σ Ei/ALi, (5-8) i= where Ei is the exposure level to chemical i, ALi is the acceptable level for chemical i, and n is the number of chemicals in the mixture. When an effect-specific HI exceeds 1, potential toxicity is a concern. In practice, EPA usually calculates the HIs by using RfDs or RfCs as the ALs. By modifying the formula, DOD can utilize other expressions for exposure and relative toxicity that might be more appropriate for deployment situations.
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124 TECHNICAL GUIDES FOR ASSESSING AND MANAGING CHEMICAL HAZARDS To apply this HI approach to military situations, the relevant MEGs should be used as the ALs. In practice, the HI method could be applied to chemicals that have similar target-organ effects. However, given the range of data sources on which the current MEGs were based, to begin considering cumulative risk the existing information in TG-230 and RD-230 would have to be reorga- nized by target organs. That will require going back to the source data in some cases to identify all of the end points considered in addition to the critical effects on which the source guidelines were based. It might be more practical to use a qualitative assessment scheme as the first stage in integrat- ing cumulative risk considerations into the MEG guidance. Repeated Exposures and Multiple Deployments Many soldiers will participate in multiple deployments during their military career. It is unlikely that multiple short-term deployments (less than or equal to14 days) involving exposures at levels below the MEGs (but not necessarily the CCEGs) will affect the likelihood of toxicity. The im- pacts of multiple long-term deployments are more relevant to force health protection. As described in previous sections, long-term MEGs for noncancer effects were based preferentially on subchronic toxicity values. However, in the many cases where only chronic toxicity values were available, those values were used. When long-term MEGs are based on chronic toxicity data they will be protective for lifetime exposures and will, therefore, also be protective for multiple deployments. When long-term MEGs are based on subchronic toxicity data, they will be protective for up to 7 years (10% of lifetime). Thus, a soldier would need to have more than 7 years of de- ployment exposures to a chemical at concentrations close to the long-term MEG before any concern would arise regarding the health impacts of those multiple deployment exposures. Furthermore, the UFs applied to the noncancer MEGs provide additional protection. For the long-term MEGs based on cancer risks, risks from multiple deployments might be viewed as irreversible over time. In a worst-case scenario with multiple exposures near MEG concentrations based on 1 × 10-4 incremental cancer risk, it is unlikely that risks from multiple deployments will contribute to total risk in excess of 1 × 10-3, which is a target risk used to develop many occupational standards. At that upper-bound risk level, risks to an individual soldier are still low compared with the background cancer risks of 0.25 (or one in four).
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MILITARY EXPOSURE GUIDELINES 125 The subcommittee was informed that DOD is working to record sol- diers’ exposures, to the extent feasible. Those records would be available if the need for retrospective analysis arose. For example, when exposures in excess of long-term MEGs occur during a deployment, it might be useful to review the records of exposures from previous deployments. However, there is no indication of an imminent need for prospective analysis of these records for the purpose of monitoring future deployments. RECOMMENDATIONS This section summarizes the major recommendations for the develop- ment and application of MEGs. The chapter itself should be consulted for more thorough descriptions and for several other recommendations that are more detailed, are more chemical-specific, or are of secondary importance. Overall, the MEGs must be re-evaluated and revised to make them more relevant to force health protection and more consistent with each other. Ideally, USACHPPM will develop a set of principles, guidelines, and proce- dures for developing MEGs de novo from the primary toxicology data. Those procedures would solidify the purpose and goals of the MEGs and would make explicit the risk-management policy decisions that underpin the removal or modification of uncertainty factors used in the existing guide- lines set by other agencies. However, the subcommittee realizes the immen- sity of that undertaking and suggests that, in the interim, revisions be made to improve the quality of the MEGs. To assist in obtaining and managing resources for this effort, DOD should analyze the resources (staff and fund- ing) needed to accomplish the recommendations, prioritize the tasks, and estimate how much time it will need to complete this work. Near-Term Revisions • Improve the quality of the MEGs by making revisions that require relatively minimal resources. Specifically, USACHPPM has applied some adjustments to the source guidelines to make them relevant to the deployed population but does not appear to have done so consistently. The following are recommended modifications: —When using TLVs to derive the 14-day and 1-year MEGs, it is unnecessarily conservative to apply a UF of 10 to account for uncer-
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126 TECHNICAL GUIDES FOR ASSESSING AND MANAGING CHEMICAL HAZARDS tainty associated with extrapolation from intermittent to continuous exposure. —All relevant MEGs should include the military adjustment factors for higher ventilation and water-intake rates. —For the six criteria air pollutants, ensure that the MEGs are ap- propriate to the military population rather than to susceptible civilian subpopulations. —Periodically review the guidelines set by other organizations that were used as sources for the MEGs. If those sources have been revised, incorporate the changes into the MEGs. Values reported in HEAST should not be used as bases for MEGs, because they have not been peer-reviewed. Additional exposure guidelines should be consulted, such as the RfCs developed by the State of California’s Office of Envi- ronmental Health Hazard Assessment. —Improve the documentation of the existing exposure guidelines by specifying the date of their establishment, the toxicity end points on which they are based, UFs used, and any special considerations in the supporting reference tables. Adjustments to the values should be made on a case-by-case basis. —Develop short-term soil MEGs for certain contaminants, particu- larly volatile organic compounds. —Re-evaluate the approach used to assess dermal exposures to CWAs. • Establish risk-management framework that focuses on action plans (i.e., responses) for when the MEGs are exceeded. Appropriate actions would include considering risk-management options for reducing or elimi- nating risks (e.g., using protective gear) and determining the appropriate medical follow-up responsibilities of DOD (e.g., documenting the exposure in medical records, tracking exposed individuals, providing long-term care) when some health risks must be borne. Mid-Term Revisions Steps in this category would result in more relevant and internally con- sistent MEGs that would be less likely to be overly conservative. However, there should be an analysis of the level of effort required for this activity relative to that required for the long-term revisions. The optimal approach to revising the MEGs would be for USACHPPM to consult the original source material (e.g., the critical study selected by EPA for an RfC or can-
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MILITARY EXPOSURE GUIDELINES 127 cer unit risk) and perform its own calculations. That would bring more unity to the guidelines. The effort would be time-consuming and would have flaws resulting from out-of-date source materials. However, it would avoid the more time-consuming tasks of literature searches and evaluations of the primary literature while providing a transparent, systematic, and uniform method of applying adjustments to exposure durations, inhalation rates, and water intake rates. It would also standardize the treatment of susceptible subpopulations. In some cases, other agencies could be asked to provide assistance. Discussions with other agencies also might reveal possibilities for accessing professionals already familiar with the assess- ments who could go back and make recalculations. Long-Term Revisions • As discussed, the source material used to derive the MEGs has inherent problems, the primary problem being the obsolescence of many of the values. Thus, simply changing the UFs and other factors will not solve all of the underlying difficulties. However, it is not feasible for USACH- PPM to create MEGs entirely de novo by beginning with literature searches. All of the agencies developing health-based guidelines struggle with the problem of obsolescence. For example, EPA is beginning a major effort to reinvigorate IRIS. That presents an opportunity to explore partnership arrangements. For example, if one agency were doing a de novo assessment on a chemical of interest to the military, it would be relatively easy for that agency to establish one guideline applicable to their interests and another applicable to the military. The word relatively is used because the major effort in assessments is evaluating and interpreting the literature, which would have to be done by the agency as well as the military. • Aggregate exposure and cumulative risk should be addressed, to the extent feasible, in each stage of revisions to the MEGs. • USACHPPM should periodically update the list of chemicals for which MEGs have been derived to include chemicals that were omitted in previous reviews (e.g., gasoline) or that have been newly identified as con- taminants. REFERENCES ATSDR (Agency for Toxic Substances and Disease Registry). 2003. Minimal Risk Levels
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128 TECHNICAL GUIDES FOR ASSESSING AND MANAGING CHEMICAL HAZARDS (MRLs). Agency for Toxic Substances and Disease Registry, Atlanta, GA. [Online]. Available: www.atsdr.cdc.gov/mrls.html [accessed Dec. 3, 2003]. Bowers, T.S., and J.S. Cohen. 1998. Blood lead slope factor models for adults: Compari- sons of observations and predictions. Environ. Health Perspect. 106(Suppl. 6):1569- 1576. Bowers, T.S., B.D. Beck, and H.S. Karam. 1994. Assessing the relationship between environmental lead concentrations and adult blood lead levels. Risk Anal. 14(2):183- 189. EPA (U.S. Environmental Protection Agency). 1996a. Air Quality Criteria for Ozone and Related Photochemical Oxidants. EPA/600/P-93/004cF. National Center for Environ- mental Assessment, Office of Research and Development, U.S. Environmental Protec- tion Agency, Washington, DC. EPA (U.S. Environmental Protection Agency). 1996b. Soil Screening Guidance: User’s Guide, 2nd Ed. Pub. No. 9355.4-23. EPA540/R-96/018. Office of Solid Waste and Emergency Response, U.S. Environmental Protection Agency, Washington, DC. [Online]. Available: http://www.epa.gov/superfund/resources/soil/index. htm#user [accessed Dec. 5, 2003]. EPA (U.S. Environmental Protection Agency). 1996c. Recommendations of the Technical Review Workgroup for Lead for an Interim Approach to Assessing Risks Associated with Adult Exposures to Lead in Soil. Environmental Criteria and Assessment Office, U.S. Environmental Protection Agency, Research Triangle Park, NC. EPA (U.S. Environmental Protection Agency). 1996d. Drinking Water Regulations and Health Advisories. EPA822-R-96-001. Office of Water, U.S. Environmental Protec- tion Agency. October 1996. EPA (U.S. Environmental Protection Agency). 1998. U.S. EPA Region 9 Preliminary Remediation Goal Tables. Office of Solid and Hazardous Waste, U.S. Environmental Protection Agency. EPA (U.S. Environmental Protection Agency). 1999a. EPA Region 3 Risk-Based Concen- tration Table. Risk Assessment, Office of Solid Waste and Emergency Response, U.S. Environmental Protection Agency. EPA (U.S. Environmental Protection Agency). 1999b. Guidance for Performing Aggregate Exposure and Risk Assessments, Draft, February 1, 1999. Office of Pesticide Pro- grams, U.S. Environmental Protection Agency. [Online]. Available: www.epa.gov/ scipoly/sap/1999/february/guidance.pdf [accessed Dec. 5, 2003]. EPA (U.S. Environmental Protection Agency). 2000. Supplementary Guidance for Con- ducting Health Risk Assessment of Chemical Mixtures. EPA/630/R-00/002. Risk Assessment Forum, U.S. Environmental Protection Agency, Washington, DC. [On- line]. Available: http://www.epa.gov/iris/backgr-d.htm [accessed Dec. 3, 2003]. EPA (U.S. Environmental Protection Agency). 2001a. Risk Assessment Guidance for Superfund—Volume I: Human Health Evaluation Manual. (Part E, Supplemental Guidance for Dermal Risk Assessment), Interim Review Draft. EPA/540/R/99/005. OSWER 9285.7-02EP. PB99-9633112. Office of Emergency and Remedial Response, U.S. Environmental Protection Agency, Washington, DC. [Online]. Available: http://www.epa.gov/oerrpage/superfund/programs/risk/ragse/ [accessed Dec.3, 2003]. EPA (U.S. Environmental Protection Agency). 2001b. General Principles for Performing Aggregate Exposure and Risk Assessments. Office of Pesticide Programs, U.S. Envi- ronmental Protection Agency. [Online]. Available: http://www.epa.gov/pesticides/ trac/science/aggregate.pdf [accessed Dec. 3, 2003].
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MILITARY EXPOSURE GUIDELINES 129 EPA (U.S. Environmental Protection Agency). 2002a. U.S. EPA Region 3 Risk-Based Concentration Table. Risk Assessment, Office of Solid Waste and Emergency Re- sponse, U.S. Environmental Protection Agency. [Online]. Available: www.epa.gov/ reg3hwmd/risk/ [updated semiannually]. EPA (U.S. Environmental Protection Agency). 2002b. U.S. EPA Region 9 Preliminary Remediation Goal Tables. Office of Solid and Hazardous Waste, U.S. Environmental Protection Agency. [Online]. Available: http://www.epa.gov/region09/waste/sfund/ prg/index.htm [updated annually]. EPA (U.S. Environmental Protection Agency). 2002c. Supplemental Guidance for Devel- oping Soil Screening Levels for Superfund Sites. OSWER 9355-4-24. Office of Solid Waste and Emergency Response, U.S. Environmental Protection Agency, Washington, DC. [Online]. Available: http://www.epa.gov/ superfund/ programs/ risk/toolthh.htm [accessed Dec. 3, 2003]. EPA (U.S. Environmental Protection Agency). 2002d. Blood Concentrations of U.S. Adult Females: Summary Statistics from Phases 1 and 2 of the National Health and Nutrition Evaluation Survey (NHANES III). OSWER 9285.7-52. Office of Solid Waste and Emergency Response, U.S. Environmental Protection Agency, Washington, DC. [Online]. Available: www.epa.gov/superfund/ programs/lead/products.htm [accessed Dec. 3, 2003]. EPA (U.S. Environmental Protection Agency). 2002e. 2002 Edition of the Drinking Water Standards and Health Advisories. EPA 822-R-02-038. Office of Water, U.S. Environ- mental Protection Agency, Washington, DC. [Online]. Available: http://www.epa. gov/waterscience/drinking/ [accessed Dec. 3, 2003]. Gaylor, D.W. 2000. The use of Haber’s law in standard setting and risk assessment. Toxi- cology 149(1):17-19. Graham, J.A., L. Folinsbee, J.M. Davis, J. Raub, and L.D. Grant. 1999. Critical health issues of criteria air pollutants. Pp. 365-397 in Toxicology of the Lung, 3rd Ed, D.E. Gardner, J.D. Crapo, and R.O. McClellan, eds. Philadelphia, PA: Taylor and Francis. Henry, C.D. 1985. Heat stress and its effects on illness and injury rates. Mil. Med. 150(6):326-329. Holmes, K.K., J.H. Shirai, K.Y. Richter, and J.C. Kissel. 1999. Field measurements of dermal soil loading in occupational and recreational activities. Environ. Res. 80(2Pt1):148-157. Kissel, J.C., K.Y. Richter, and R.A. Fenske. 1996. Field measurement of dermal soil load- ing attributed to various activities: Implications for exposure assessment. Risk Anal. 16(1):115-125. Kissel, J.C., J.H. Shirai, K.Y. Richter, and R.A. Fenske. 1998. Investigation of dermal contact with skin in controlled trials. J. Soil Contam. 7(6):737-752. NRC (National Research Council). 1986. Criteria and Methods of Preparing Emergency Exposure Guidance Level (EEGL), Short-Term Public Emergency Guidance Level (SPEGL), and Continuous Exposure Guidance Level (CEGL) Documents. Washing- ton, DC: National Academy Press. NRC (National Research Council). 2000. Strategies to Protect the Health of Deployed U.S. Forces: Analytical Framework for Assessing Risks. Washington, DC: National Acad- emy Press. O’Flaherty, E.J. 1993. Physiologically based models for bone-seeking elements. IV: Kinetics of lead disposition in humans. Toxicol. Appl. Pharmacol. 118(1):16-29. USACHPPM (U.S. Army Center for Health Promotion and Preventive Medicine). 1999. Derivation of Health-based Environmental Screening Levels for Chemical Warfare
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130 TECHNICAL GUIDES FOR ASSESSING AND MANAGING CHEMICAL HAZARDS Agents. U.S. Army Center for Health Promotion and Preventive Medicine, Aberdeen Proving Ground, MD, and Oak Ridge National Laboratory, Oak Ridge, TN. USACHPPM (U.S. Army Center for Health Promotion and Preventive Medicine). 2002a. Chemical Exposure Guidelines for Deployed Military Personnel. Technical Guide 230. U.S. Army Center for Health Promotion and Preventive Medicine. January 2002. [Online]. Available: http://chppm-www.apgea.army.mil/deployment/ [accessed No- vember 25, 2003] USACHPPM (U.S. Army Center for Health Promotion and Preventive Medicine). 2002b. Chemical Exposure Guidelines for Deployed Military Personnel. A Companion Docu- ment to USACHPPM Technical Guide (TG) 230 Chemical Exposure Guidelines for Deployed Military Personnel. Reference Document (RD) 230. U.S. Army Center for Health Promotion and Preventive Medicine January 2002. [Online]. Available: http://chppm-www.apgea.army. mil/deployment/ [accessed November 25, 2003] U.S. Department of the Army. 1999. Sanitary Control and Surveillance of Field Water Supplies, Draft, May 1999. Technical Bulletin, Medical 577. (as cited in USACHPPM 2002a) Wester, R.C., H.I. Maibach, L. Sedik, J. Melendres, C.I. Liao, and S. DiZio. 1992. Percutaneous absorption of [14C]chlordane from soil. J. Toxicol. Environ. Health 35(4):269-277. WHO (World Health Organization). 2000. Air Quality Guidelines for Europe, 2nd Ed. European Series No 91. Copenhagen: World Health Organization.
Representative terms from entire chapter: