Potential Health Risks to DOD Firing-Range Personnel from Recurrent Lead Exposure (2013) / Chapter Skim
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3 Toxicokinetics of Lead
3 Toxicokinetics of Lead
Pages 47-61
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From page 47... ...
However, smaller fume particles may agglomerate into larger particles before inhalation or ingestion. About 50% of the lead deposited in the respiratory tract is absorbed and reaches the systemic circulation whereas net absorption of ingested lead from the adult digestive tract is appreciably lower (less than 8% to 10%)
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From page 48... ...
document that several personal behaviors can increase lead dose, including tobacco-smoking, eating, and drinking in the workplace and inadequate personal hygiene before leaving the workplace. The OSHA standard therefore mandates no eating, drinking, or smoking in areas that have potential lead exposure and separate facilities for changing clothes and washing before returning home.
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From page 49... ...
. EXPOSURE Air, water, surfaces "Cumulative" dose tibia lead level Lungs/GI tract Trabecular Cortical bone > 90% bone Circulation Blood 2-5% Target organ tissues 2-8% Liver Kidney PLASMA "Recent" dose blood lead level EXCRETION FIGURE 3-1 Compartmental model for lead (modified from O'Flaherty 1993)
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It is standard practice in the United States and around the world to develop occupational exposure and dose standards that protect all workers, including the most susceptible, rather than to perform genetic screening and exclude higher-risk people from work settings. MEASURING INTERNAL LEAD DOSE Because of its wide distribution in the body, biologic measures of lead dose in a number of tissues -- including blood, plasma, umbilical cord blood, hair, fingernails and toenails, breast milk, urine, semen, soft tissue, and bone -- are available (see review by Hu et al.
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From page 51... ...
or tibia lead concentrations are the preferred dose metrics for studying longer-latency, chronic health effects of cumulative dose. OSHA, however, did not consider lead bioaccumulation (in bone)
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From page 52... ...
For some health outcomes, such as pregnancy, there are critical exposure periods during which a given lead dose could have a much greater deleterious effect than if it occurred at other stages of life. As the working lifetime increases and cumulative dose steadily rises, bone lead stores contribute more to current BLLs, so a single BLL later in the working career can reflect exposure earlier in employment, when BLLs may have been much higher.
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. In the late 1970s, OSHA sought the development of a dosimetry model that could predict the distribution of BLLs in a given worker population in response to changing air lead concentrations.
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. At low lead concentrations, kinetics are linear; nonlinear kinetics start when lead concentration in erythrocytes reaches 60 μg/dL, which corresponds to BLL of about 25 μg/dL (Leggett 1993)
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From page 55... ...
Their general form accounts for multiple sources of lead exposure and follows this relationship: BLL = A[(air lead concentration) + (B1{food lead concentration})
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From page 56... ...
Statistical and Monte-Carlo methods can also be used to estimate values of PBPK model parameters and to characterize uncertainty in PBPK model predictions. LEAD DOSE AND HEALTH For its evaluation of health effects associated with lead exposure in Chapters 4 and 5, the committee sought to find evidence that health effects could occur at exposures and doses lower than those specified in the OSHA lead standard.
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would have an average BLL of 40 µg/dL; that is, the PEL was selected to keep BLLs around 40 µg/dL on the average. Thus, if the committee found evidence to suggest that health effects occur below that BLL (or below the CBLIs or tibia lead levels that would result over time from long-duration BLLs at lower levels)
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1975. An epidemiologic approach to community air lead exposure using personal air samplers.
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1997. Age and secular trends in bone lead levels in middle-aged elderly men: Three-year longitudinal fol low-up in the Normative Aging Study.
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1995. Time integrated blood lead concentration is a valid surrogate for estimating the cumulative lead dose assessed by tibial lead measurement.
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2011. Longitudinal changes in bone lead levels: The VA Normative Aging Study.
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