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OCR for page 164
6
Conclusions
The Occupational Safety and Health Administration (OSHA) lead stan-
dard for general industry applies to US military firing ranges and was the main
focus of the committee’s effort to determine whether “current exposure stan-
dards 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 cur-
rent permissible exposure limit (PEL) of 50 µg/m3 (8-hour time-weighted aver-
age). 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 cur-
rent OSHA exposure standards used on firing ranges are protective. The com-
mittee used the following questions to guide the presentation of its conclusions:
Are OSHA’s guidelines for blood lead levels (BLLs) adequate to pro-
tect 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 Toxi-
164
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Conclusions 165
cology Program [NTP]”. In keeping with its charge, the committee initially
evaluated key literature presented in the NTP’s 2012 Monograph on Health Ef-
fects 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. Dur-
ing 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. When-
ever possible, the committee based its conclusions on occupational and other
studies of relevance to DOD personnel that work at firing ranges. Special con-
sideration 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 analy-
ses; these included tobacco use, alcohol consumption, and coexposure to other
metals and chemicals. The committee’s conclusions emphasized outcomes asso-
ciated with clinical disease rather than early biologic effects. For example, the
committee considered decrements in circulating hemoglobin to be more impor-
tant than increases in zinc protoporphyrin. In reaching its conclusions, the com-
mittee 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 conclu-
sion 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 condi-
tions 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
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166 Potential Health Risks to DOD Firing-Range Personnel
exposures that result in BLLs of 40 µg/dL or below could result in material im-
pairment of health or functional capacity in DOD firing-range workers. It is im-
portant to note that BLL generally reflects short-latency, acute health effects of
recent lead exposure. However, to some extent, BLLs later in life reflect cumu-
lative lead exposure, so the interpretation of studies of BLLs later in life is prob-
lematic with regard to defining a “threshold level” for a health effect. The com-
mittee 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 un-
der 40 µg/dL is not sufficiently protective of personnel who have repeated lead
exposures on firing ranges. The committee concludes that the evidence is suffi-
cient to infer causal relationships between BLLs under 40 µg/dL and impaired
neurologic, hematopoietic, renal, reproductive, and cardiovascular function. Ex-
amples 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).
1
The reader is referred to Chapter 4 for additional details about individual studies.
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Conclusions 167
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 be-
tween 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 µg-
years/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 commit-
tee examined evidence that suggested whether a CBLI of under 1,600 µg-
years/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).
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168 Potential Health Risks to DOD Firing-Range Personnel
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 im-
aging (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 cen-
tral 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 sur-
veillance. If it is determined that airborne lead concentrations exceed the action
level for more than 30 days/year, an employer must provide a medical surveil-
lance 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 ef-
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Conclusions 169
fects. 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 confi-
dence in answering the questions above. However, several data gaps on related
subjects were identified during the committee’s deliberations, including the fol-
lowing:
Epidemiology studies of firing-range personnel are few.
To the committee’s knowledge, size distribution and chemical speci-
ation of airborne lead particles associated with firing ranges have not been per-
formed. 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 Occupa-
tional and Environmental Clinics (AOEC), and the Council of State and Territo-
rial Epidemiologists (CSTE)—have called for more protective guidelines. For
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170 Potential Health Risks to DOD Firing-Range Personnel
example, ACOEM (2010) has recommended medical removal of workers who
have BLLs of 20 µg/dL or higher. AOEC (2007) has recommended more strin-
gent 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 preg-
nant 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 develop-
mental 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 fir-
ing-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 fir-
ing-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 expo-
sure 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 ammu-
nition and that the use of jacketed and other alternative bullets may entail in-
creased cost.
Continuing improvement in range design and ventilation. The commit-
tee recognizes that some modifications may be difficult to implement, particu-
larly as “retrofits” of existing ranges, and that high-efficiency ventilation is ex-
pensive to install and operate.
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Conclusions 171
Range cleaning. Scott et al. (2012) found that although ventilation is
important for controlling lead exposures, housekeeping can also have a substan-
tial 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 rec-
ommendations 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 work-
ers had washed their hands or bathed. More recent investigations have demon-
strated that washing with soap and water is not effective in removing lead from
skin. Esswein et al. (2011) found that hand decontamination, rather than wash-
ing, is required to ensure complete removal of lead. A mixture of isostearamido-
propyl morpholine lactate and citric acid applied with a textured absorbent mate-
rial 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 con-
trol 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 impor-
tance of housekeeping.
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