health effect. EPA’s AQCD (2006) also identified health effects associated with BLLs under 10 μg/dL. EPA’s Integrated Science Assessment for Lead (2012) affirmed many of the conclusions reached in the AQCD (2006). The reader is referred to specific conclusions reached by those organizations and the committee’s conclusions with respect to their relevance to Department of Defense personnel who work on firing ranges. The committee also performed its own search for recent relevant literature on the health effects of lead to supplement those evaluations.
The adult nervous system is a critical target for the toxic effects of lead. Effects on the central nervous system of lead workers include dose-related changes in cognitive and psychomotor performance and mood, neurodegenerative diseases, and neurophysiologic changes in the auditory, visual, and balance systems. Effects of occupational lead exposure on the peripheral nervous system at BLLs of 60-70 μg/dL are manifested as motor weakness with abnormalities in motor and sensory nerve conduction. No peripheral motor or sensory symptoms are known to occur at BLLs under 40 μg/dL, but sensory nerve function is associated with lead dose.
Potential modes of action for lead neurotoxicity include oxidative stress, inhibition of enzymes needed for energy production, decreased levels of neurotransmitters and altered neurotransmitter release, and increased permeability of the blood-brain barrier (EPA 2012). Ultimately, lead-induced neurotoxicity in adults consists of changes in brain structure and neurochemistry, including white-matter changes, reduction in gray matter, and alterations in brain metabolites.
Conclusions from the Environmental Protection Agency 2006 and 2012 and National Toxicology Program 2012 Lead Documents
Environmental Protection Agency 2006 Air Quality Criteria Document
EPA’s 2012 Integrated Science Assessment for Lead (Second External Review Draft) focused on updating the 2006 Air Quality Criteria Document for Lead (EPA 2006), so a summary of the key neurotoxic effects of lead in adults from the earlier document will be presented first.
Studies of the effects of aging and their relationship with environmental lead exposure included the Veterans’ Administration Normative Aging Study established in 1961 in Boston and consisting of 2,280 healthy men 21-80 years old who are examined every 3 years (Payton et al. 1998; Rhodes et al. 2003; Wright et al. 2003; Weisskopf et al. 2004), the Kungsholmen Project on aging and dementia in Sweden (Nordberg et al. 2000), and the third National Health and Nutrition Examination Survey (NHANES III) (Krieg et al. 2005). There was