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Committee on Potential Health Risks from Recurrent Lead Exposure of DOD Firing-Range Personnel; Committee on Toxicology; Board on Environmental Studies and Toxicology; Division on Earth and Life Studies; National Research Council. Potential Health Risks to DOD Firing-Range Personnel from Recurrent Lead Exposure. Washington (DC): National Academies Press (US); 2012 Dec 3.

Cover of Potential Health Risks to DOD Firing-Range Personnel from Recurrent Lead Exposure

Potential Health Risks to DOD Firing-Range Personnel from Recurrent Lead Exposure.

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6Conclusions

The Occupational Safety and Health Administration (OSHA) lead standard for general industry applies to US military firing ranges and was the main focus of the committee's effort to determine whether “current exposure standards used at ranges are protective”. In addressing its charge, the committee initially evaluated the firing-range environment and associated occupational lead exposures (Chapter 1). Atmospheric lead concentrations collected by the US Army, US Air Force, and US Navy during the last few years showed that mean air lead concentrations on military firing ranges were often above OSHA's current permissible exposure limit (PEL) of 50 μg/m3 (8-hour time-weighted average). The committee reviewed the historical development of the current OSHA lead standard (Chapter 2) and the toxicokinetics of lead (Chapter 3) and then considered the adverse health effects of lead with respect to noncancer end points (Chapter 4) and cancer outcomes (Chapter 5).

In this chapter, the committee presents its conclusions as to whether current OSHA exposure standards used on firing ranges are protective. The committee used the following questions to guide the presentation of its conclusions:

  • Are OSHA's guidelines for blood lead levels (BLLs) adequate to protect Department of Defense (DOD) firing-range personnel?
  • Is the current OSHA PEL adequately protective of DOD firing-range personnel?
  • Is the current OSHA action level for medical surveillance appropriate?
  • Were data gaps identified in answering the questions above? Is research needed to fill those gaps?

The committee's charge also stated that “information will be evaluated on recurrent lead exposures at such firing ranges, and relevant toxicological and epidemiological information on any carcinogenic and non-carcinogenic effects of exposures to lead will be evaluated. The evaluated information will include reviews by the Environmental Protection Agency [EPA] and the National Toxicology Program [NTP]”. In keeping with its charge, the committee initially evaluated key literature presented in the NTP's 2012 Monograph on Health Effects of Low-level Lead, the EPA's 2006 Air Quality Criteria Document [AQCD] for Lead Final Report, the 2012 EPA's Integrated Science Assessment for Lead (Second External Review Draft), the International Agency for Research on Cancer (IARC) monograph Inorganic and Organic Lead Compounds (IARC 2006), and the 2004 and 2011 editions of the NTP Report on Carcinogens. The committee then considered studies that were not included in those reviews. During this step, the committee gave greater weight to other systematic reviews and studies that included meta-analyses.

The committee used additional considerations to narrow its work. Health-effects data on BLLs below 40 μg/dL were primarily considered because the current OSHA standard aims to maintain BLLs below that concentration. Whenever possible, the committee based its conclusions on occupational and other studies of relevance to DOD personnel that work at firing ranges. Special consideration was given to women who might be pregnant or nursing because of the well-known effects of lead on the developing nervous system. The committee also favored studies that considered potential covariates in their statistical analyses; these included tobacco use, alcohol consumption, and coexposure to other metals and chemicals. The committee's conclusions emphasized outcomes associated with clinical disease rather than early biologic effects. For example, the committee considered decrements in circulating hemoglobin to be more important than increases in zinc protoporphyrin. In reaching its conclusions, the committee considered the weight of evidence and relied most heavily on findings of lead-induced adverse health effects that had been replicated in multiple peer-reviewed studies.

The committee's conclusions are based on noncancer end points. Although IARC, NTP, and EPA have identified lead as probably carcinogenic in humans, such findings were based largely on studies of laboratory animals. The available human studies on cancer were insufficient for the committee to draw a conclusion about BLLs that might be associated with cancer in humans.

ARE OCCUPATIONAL SAFETY AND HEALTH GUIDELINES FOR BLOOD LEAD LEVELS ADEQUATE TO PROTECT DEPARTMENT OF DEFENSE FIRING-RANGE PERSONNEL?

The primary purpose of the Occupational Safety and Health Act (29 USC 655 et seq) is to ensure, to the extent possible, safe and healthful working conditions for every American worker over his or her working lifetime. OSHA's lead standard requires that a worker who has a single BLL over 60 μg/dL or three BLLs averaging over 50 μg/dL be removed from performing lead work until his or her BLL is under 40 μg/dL on two occasions. Thus, the current OSHA lead standard recognizes a level of concern for workers who have BLLs of 40–60 μg/dL or higher. The committee therefore focused its attention on whether lead exposures that result in BLLs of 40 μg/dL or below could result in material impairment of health or functional capacity in DOD firing-range workers. It is important to note that BLL generally reflects short-latency, acute health effects of recent lead exposure. However, to some extent, BLLs later in life reflect cumulative lead exposure, so the interpretation of studies of BLLs later in life is problematic with regard to defining a “threshold level” for a health effect. The committee also recognized that peak BLLs, average BLLs, and current BLLs could be expected to have different associations with health outcomes, depending on mechanism of action, latency, and other considerations.

The committee concludes that the current OSHA standard of a BLL of under 40 μg/dL is not sufficiently protective of personnel who have repeated lead exposures on firing ranges. The committee concludes that the evidence is sufficient to infer causal relationships between BLLs under 40 μg/dL and impaired neurologic, hematopoietic, renal, reproductive, and cardiovascular function. Examples of acute and chronic adverse health effects that have been reported in the literature and are relevant for DOD firing-range personnel (and their associated mean BLL, benchmark dose, or lowest observed BLLs) are1

  • Reduced fetal growth and low birth weight (maternal BLL under 5 μg/dL).
  • Increased cardiovascular-disease mortality (BLL 8 μg/dL or higher).
  • Increased serum creatinine, an indicator of renal injury (BLL 8–12 μg/dL).
  • Hearing loss (BLL under 10 μg/dL).
  • Increased blood pressure (BLL under 10 μg/dL).
  • Preterm birth (BLL under 10 μg/dL; evidence on this level is growing stronger).
  • Altered postnatal development and growth (maternal BLL under 10 μg/dL).
  • Impaired balance (BLL = 14 μg/dL, identified as a benchmark dose).
  • Neuronal loss and myelin alterations (BLL = 16.9 μg/dL).
  • Slowed visual evoked potentials (BLL = 17–20 μg/dL).
  • Decreased psychomotor speed and dexterity and executive function (BLL = 18 μg/dL).
  • Decreased erythrocyte, hematocrit, and hemoglobin concentrations (BLL = 20–30 μg/dL).
  • Decreased creatinine clearance and glomerular filtration rate, indicators of renal injury (BLL = 20–30 μg/dL).
  • Altered parasympathetic and sympathetic activity (BLL = 20 μg/dL or higher).
  • Slowed brainstem auditory evoked potentials (BLL = 26–30 μg/dL).
  • Altered verbal memory and learning and reaction time (BLL = 26–30 μg/dL).
  • Changes in electric activity of the brain evidenced by slow alpha rhythm (BLL = 29 μg/dL).
  • Altered peripheral sensory nerve function (BLL = 30 μg/dL).
  • Increased plasma renin activity, angiotensin, angiotensin-converting enzyme, and aldosterone (BLLs = 30–40 μg/dL; these changes are indicative of alterations in renal endocrine functioning and may be responsible, in part, for the increases in blood pressure observed with high BLLs).

The committee also considered studies that reported an association between cumulative lead dose, as assessed by cumulative blood lead index (CBLI) or bone lead concentration, and adverse health outcomes. Associations of health outcomes with CBLI or tibia lead concentrations are probably representative of longer-latency, chronic health effects of cumulative dose. In considering CBLI and bone lead data, the committee used the following assumptions: a BLL of 40 μg/dL over a 40-y working lifetime would be equivalent to a CBLI of 1,600 μgyears/dL, and this CBLI is roughly equivalent to a bone lead concentration of 40–80 μg/g (on the basis of the published relation that tibia lead can be estimated as 2.5–5% of the CBLI) (Hu et al. 2007; Healey et al. 2008). Thus, the committee examined evidence that suggested whether a CBLI of under 1,600 μgyears/dL or a bone lead concentration of under 40–80 μg/g may be associated with adverse health effects of lead exposure.

Because the current OSHA standard does not address CBLI or bone lead concentrations directly, the committee considered data on this measurement to be supportive evidence for its conclusions. Such data included the following:

  • Neuronal loss and myelin alterations of brain measured with magnetic resonance spectroscopy (mean bone lead = 7 μg/g).
  • Hypertension (bone lead concentrations of 13–38 μg/g).
  • Slow alpha activity on electroencephalogram (mean bone lead = 26 μg/g, mean CBLI = 546 μg-years/dL).
  • Increased cardiovascular mortality (bone lead concentration over 35 μg/g).
  • Increased incidence of ischemic heart disease (bone lead concentrations over 35 μg/g).
  • Decreased hemoglobin and hematocrit (bone lead concentration around 35 μg/g, the difference between the highest and lowest quintiles of bone lead).
  • Depression symptoms (mean bone lead = 37 μg/g).
  • Altered quantitative sensory function in peripheral nerves (mean bone lead = 37 μg/g, mean CBLI = 546 μg-years/dL).
  • Altered psychomotor speed and dexterity (mean bone lead = 38 μg/g).
  • Slowed brainstem auditory evoked potentials (mean CBLI = 723–934 μg-years/dL).
  • Altered psychomotor speed, dexterity, verbal memory, and executive function (mean CBLI = 765 μg-years/dL).
  • White matter change in the brain measured by magnetic resonance imaging (mean bone lead = 39 μg/g, mean CLBI = 826 μg-years/dL).

IS THE CURRENT OCCUPATIONAL SAFETY AND HEALTH ADMINISTRATION PERMISSIBLE EXPOSURE LIMIT ADEQUATELY PROTECTIVE OF DEPARTMENT OF DEFENSE FIRING-RANGE PERSONNEL?

The ability to predict BLLs on the basis of air lead concentrations is central to the development of the OSHA standard's PEL. The OSHA PEL of 50 μg/m3 was set to result in the average lead worker's having a BLL under 40 μg/dL. That BLL was judged by the committee to be inadequate for protecting personnel who had repeated lead exposures on firing ranges (see response to the first question above); thus, the OSHA PEL for lead would also be insufficiently protective.

The committee was not able to estimate an air lead concentration that would protect firing-range workers from adverse health effects that could occur at BLLs of 40 μg/dL or lower, but a concentration below the current PEL of 50 μg/m3 clearly is warranted. As discussed in Chapter 3, the OSHA PEL was based on a model produced by the Massachusetts Institute of Technology Center for Policy Alternatives (CPA) (Ashford et al. 1977). The CPA model relied on data from manufacturing operations that may not be directly relevant to firing-range exposures, including differences in lead aerosol particle size, frequency and duration of exposure, assumptions regarding lung deposition and absorption of inhaled particles, and contributions from routes of exposure other than inhalation.

IS THE CURRENT OCCUPATIONAL SAFETY AND HEALTH ADMINISTRATION ACTION LEVEL FOR MEDICAL SURVEILLANCE APPROPRIATE?

The OSHA lead standard also creates an air action level for medical surveillance. If it is determined that airborne lead concentrations exceed the action level for more than 30 days/year, an employer must provide a medical surveillance program that consists of biologic monitoring and medical examinations and consultations. The OSHA action level for airborne lead exposure is 30 μg/m3 (8-hour time-weighted average). On the basis of the CPA model (Ashford et al. 1977), that exposure concentration would mean that the average lead worker with 1 year of work experience would have a BLL of about 30 μg/dL. Workers with longer job duration would have higher BLLs. As noted above in response to the first question, BLLs under 30 μg/dL have been linked to renal, neurologic, hematologic, reproductive, cardiovascular, and developmental effects. Thus, the action level for lead would have to be lowered in conjunction with the PEL if the lower PEL is still deemed insufficient to protect all workers. In setting the action level, consideration should also be given to the contribution of oral (hand-to-mouth) exposure to lead.

WERE DATA GAPS IDENTIFIED IN ANSWERING THE QUESTIONS ABOVE? IS RESEARCH NEEDED TO FILL THOSE GAPS?

The committee did not identify any data gaps that threatened its confidence in answering the questions above. However, several data gaps on related subjects were identified during the committee's deliberations, including the following:

  • Epidemiology studies of firing-range personnel are few.
  • To the committee's knowledge, size distribution and chemical speciation of airborne lead particles associated with firing ranges have not been performed. Such information could be used to estimate the bioavailability of the lead particles found in firing-range air.
  • The CPA model used in the OSHA standard to predict BLLs from air lead concentrations may not be appropriate for direct application to firing-range personnel, so physiologically based pharmacokinetic or other dosimetry models may need to be developed for this purpose. Those models could consider other biometrics of exposure, such as bone and semen lead levels.
  • The extent to which occupational oral exposure to lead-based dusts found in the firing-range environment by hand-to-mouth contact contributes to total lead body burden has not been adequately characterized.
  • The immunotoxicity of low-level lead exposure has been incompletely studied in adults.
  • Interactions between noise and lead exposure have been incompletely evaluated.

POTENTIAL RISK-ASSESSMENT OPTIONS

Many groups have proposed alternative management guidelines for BLLs. Most recently, an expert group recommended that BLLs be kept below 20 μg/dL to prevent the acute effects of recent doses (Schwartz and Hu 2007), and this has been supported by the American College of Occupational and Environmental Medicine (ACOEM 2010). For the prevention of the chronic health effects of cumulative doses, the group recommended that tibia lead levels not be allowed to exceed 15 μg/g; this could be achieved, for example, by keeping the average BLL below 10 μg/dL for 40 y (Hu et al. 2007; Schwartz and Hu 2007).

Professional organizations—such as ACOEM, the Association of Occupational and Environmental Clinics (AOEC), and the Council of State and Territorial Epidemiologists (CSTE)—have called for more protective guidelines. For example, ACOEM (2010) has recommended medical removal of workers who have BLLs of 20 μg/dL or higher. AOEC (2007) has recommended more stringent guidelines for medical management of lead-exposed workers, which have been incorporated into DOD's guidance for occupational medical examinations and surveillance (DOD 2007). CSTE (2009) has recommended that the case definition of elevated BLLs in adults be changed from 25 μg/dL to 10 μg/dL. All those organizations recommend that BLLs be kept under 5 μg/dL in pregnant women to reduce the risk of spontaneous abortion.

The US Centers for Disease Control and Prevention (CDC) has developed guidelines that recommend followup activities and interventions beginning at a BLL of 5 μg/dL in pregnant women (CDC 2010) and children (CDC 2012). That BLL is not a “level of concern” or an allowable exposure but rather a level at which it may be prudent to initiate testing and interventions to reduce lead exposure. CDC found convincing evidence that prenatal lead exposure impairs children's neurodevelopment and so places them at increased risk for developmental delay, reduced IQ, and behavioral problems (CDC 2010). The committee agrees that there is a need for additional protection of women of childbearing age, especially pregnant and lactating women.

ADDITIONAL CONSIDERATIONS

It was unclear to the committee what the potential health risks to DOD firing-range personnel might be, because BLL data specifically on DOD firing-range workers were limited. However, data on airborne concentrations of lead on DOD firing ranges indicate that the current OSHA PEL is exceeded in the performance of some job duties—in some cases by several orders of magnitude. Thus, DOD should consider analyzing BLLs of a representative sample of firing-range workers in all the services and comparing them with BLLs linked to adverse health outcomes so that it can understand potential risks and guide risk-management decisions regarding its ranges. Consideration should be given to risk analyses of available control options to determine how to minimize exposure to lead. Control options that could be explored in such analyses include the following:

  • Ammunition substitution. Exposure of shooters to airborne lead might be reduced by replacing traditional lead bullets with nylon-clad, copper-jacketed, zinc-based, or other forms of ammunition. However, the committee recognizes that training requirements may limit the use of those forms of ammunition and that the use of jacketed and other alternative bullets may entail increased cost.
  • Continuing improvement in range design and ventilation. The committee recognizes that some modifications may be difficult to implement, particularly as “retrofits” of existing ranges, and that high-efficiency ventilation is expensive to install and operate.
  • Range cleaning. Scott et al. (2012) found that although ventilation is important for controlling lead exposures, housekeeping can also have a substantial effect on lead contamination on surfaces on and around a shooting range. Even on ranges that have good ventilation and that use ammunition with lead-free primers, poor housekeeping or failing to decontaminate a range thoroughly before switching primers may adversely affect lead exposures.
    The Navy Environmental Health Center notes, in its Indoor Firing Ranges Industrial Hygiene Technical Guide (NEHC 2002), that although there are no established limits for surface lead contamination in workplaces, OSHA (1993) has indicated in a compliance instruction for the construction industry (CPL 2-2.58) that an acceptable lead loading for nonlead work areas should be 200 μg/ft2. Appendix D of the technical guide suggests clearance levels of 200 μg/ft2 for interior floors and horizontal surfaces and 800 μg/ft2 for exterior concrete.
  • Hygiene practices. Strict adherence to the OSHA lead-standard recommendations for personal hygiene is critical, and additional hygiene practices should also be considered. Sato and Yano (2006) detected lead contamination on the hands of lead-handling workers at a battery-recycling plant even after workers had washed their hands or bathed. More recent investigations have demonstrated that washing with soap and water is not effective in removing lead from skin. Esswein et al. (2011) found that hand decontamination, rather than washing, is required to ensure complete removal of lead. A mixture of isostearamidopropyl morpholine lactate and citric acid applied with a textured absorbent material was almost 100% effective in removing lead from skin. They suggest that the best method for preventing hand-to-mouth exposure to lead may be skin decontamination and a colorimetric method to detect remaining contamination.

If DOD's occupational exposure limit for lead is lowered, surface and skin decontamination is likely to play an even more important role in effective control of employee exposures than in the past. It will be important for updated guidelines to address the importance of decontamination in more detail and with greater precision. When possible, quantitative levels of contamination should be included in the guidelines rather than qualitative statements regarding the importance of housekeeping.

REFERENCES

  • ACOEM (American College of Occupational and Environmental Medicine). Recommendation to OSHA Regarding Blood Lead Levels; Blood Lead Task Force Proposal to the ACOEM Board of Directors; March 25, 2010; 2010. [June 20, 2012]. {online]. Available: http://www​.acoem.org/BloodLeadLevels​.aspx.
  • AOEC (Association of Occupational and Environmental Clinics). Medical Management Guidelines for Lead-Exposed Adults, Revised; April 24, 2007; 2007. [Apr. 16, 2012]. [online]. Available: http://www​.aoec.org/documents​/positions/MMG_FINAL.pdf.
  • Ashford NA, Gecht RD, Hattis DB, Katz JI. Center for Policy Alternatives, Massachusetts Institute of Technology; Cambridge, MA: 1977. The Effects of OSHA Medical Removal Protection on Labor Costs of Selected Lead Industries. (CPA Report No. CPA-77/11. NTIS PB-278653).
  • CDC (Centers for Disease Control and Prevention). Guidelines for the Identification and Management of Lead Exposure in Pregnant and Lactating Women. U.S; November 2010; Atlanta, GA: Department of Health and Human Services; 2010. [July 27, 2012]. [online]. Available: http://www​.cdc.gov/nceh​/lead/publications​/LeadandPregnancy2010.pdf.
  • CDC (Centers for Disease Control and Prevention). A Renewed Call for Primary Prevention Report of the Advisory Committee on Childhood Lead Poisoning Prevention. 2012. [October 1, 2012]. Low Level Lead Exposure Harms Children. http://www​.cdc.gov/nceh​/lead/ACCLPP/Final_Document_030712​.pdf .
  • CSTE (Council of State and Territorial Epidemiologists). Public Health Reporting and National Notification for Elevated Blood Lead Levels; Position Statement 09-OH-02, Revised; June 10, 2009; 2009. [Apr. 16, 2012]. [online]. Available: http://www​.cste.org/dnn​/AnnualConference​/PositionStatements/09PositionStatements/tabid/333/Default​.aspx.
  • DoD (U.S. Department of Defense). Department of Defense, Undersecretary of Defense for Acquisition, Technology and Logistics; Washington, DC: 2007. [Apr. 16, 2012]. Occupational Medical Examinations and Surveillance Manual DoD 6055.05-M. U.S. [online]. Available: http://www​.dtic.mil/whs​/directives/corres/pdf/605505mp.pdf.
  • Esswein EJ, Boeniger MF, Ashley K. Handwipe method for removing lead from skin. J. ASTM Int. 2011;8(5):1–10.
  • Healey N, Chettle DR, McNeill FE, Fleming DE. Uncertainties in the relationship between tibia lead and cumulative blood lead index. Environ. Health Perspect. 2008;116(3):A109–A110. [PMC free article: PMC2265029] [PubMed: 18335076]
  • Hu H, Shih R, Rothenberg S, Schwartz BS. The epidemiology of lead toxicity in adults: Measuring dose and consideration of other methodologic issues. Environ. Health Perspect. 2007;115(3):455–462. [PMC free article: PMC1849918] [PubMed: 17431499]
  • IARC (International Agency for Research on Cancer). IARC Monographs on the Evaluation of Carcinogenic Risks to Humans Vol. 87. Lyon, France; IARC: 2006. [Oct. 2, 2012]. Inorganic and Organic Lead Compounds. [online]. Available: http://monographs​.iarc​.fr/ENG/Monographs/vol87/index.php.
  • NEHC (Navy Environmental Health Center). Indoor Firing Ranges, Industrial Hygiene Technical Guide, Technical Manual NEHC-TM6290.99–10 Rev. 1; Navy Environmental Health Center, Bureau of Medicine and Surgery; May 2002; 2002. [Dec. 19, 2011]. [online]. Available: http://www​.nmcphc.med​.navy.mil/downloads​/IH/indoor_firing_range.pdf.
  • OSHA (Occupational Safety and Health Administration). Lead Exposure in Construction; Interim Final Rule--Inspection and Compliance Procedures OSHA Instruction CPL 2-2.58; Occupational Safety and Health Administration, Office of Health Compliance Assistance; December 13, 1993; 1993. [online]. Available: http://www.osha.gov/pls/oshaweb/owadisp.show_document?p_id=1570&p_table=DIRECTIVESaccessed Nov 28, 2012]
  • Sato M, Yano E. The association between lead contamination on the hand and blood lead concentration: A workplace application of the sodium sulphide (Na2S) test. Sci. Total Environ. 2006;363(1–3):107–113. [PubMed: 16153691]
  • Schwartz BS, Hu H. Adult lead exposure: Time for change. Environ. Health Perspect. 2007;115(3):451–454. [PMC free article: PMC1849904] [PubMed: 17431498]
  • Scott EE, Pavelchak N, DePersis R. Impact of housekeeping on lead exposure in indoor law enforcement shooting ranges. J. Occup. Environ. Hygiene. 2012;9(3):D45–D51. [PubMed: 22353015]

Footnotes

1

The reader is referred to Chapter 4 for additional details about individual studies.

Copyright 2013 by the National Academy of Sciences. All rights reserved.
Bookshelf ID: NBK206971

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