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PBHA
required in personal automobiles since 1972. Lead is found in soil near abandoned industrial sites where
lead may have been used. Water transported through lead or lead-soldered pipe will contain some lead
with higher concentrations found in water that is weakly acidic. Some foods (for example: moonshine
distilled in lead pipes) and some traditional home medicines contain lead. Lead expresses its toxicity by
several mechanisms. It avidly inhibits aminolevulinic acid dehydratase (ALA-D) and ferrochelatase, 2 of
the enzymes that catalyze synthesis of heme; the end result is decreased hemoglobin synthesis resulting in
anemia. Lead also is an electrophile that avidly forms covalent bonds with the sulfhydryl group of
cysteine in proteins. Thus, proteins in all tissues exposed to lead will have lead bound to them. The most
common sites affected are epithelial cells of the gastrointestinal tract and epithelial cells of the proximal
tubule of the kidney. The typical diet in the United States contributes 1 to 3 mcg of lead per day, of which
1% to 10% is absorbed; children may absorb as much as 50% of the dietary intake, and the fraction of
lead absorbed is enhanced by nutritional deficiency. The majority of the daily intake is excreted in the
stool after direct passage through the gastrointestinal tract. While a significant fraction of the absorbed
lead is rapidly incorporated into bone and erythrocytes, lead ultimately distributes among all tissues, with
lipid-dense tissues such as the central nervous system being particularly sensitive to organic forms of lead.
All absorbed lead is ultimately excreted in the bile or urine. Soft-tissue turnover of lead occurs within
approximately 120 days. Avoidance of exposure to lead is the treatment of choice. However, chelation
therapy is available to treat severe disease. Oral dimercaprol may be used in the outpatient setting except
in the most severe cases.
Useful For: Detecting lead toxicity
Interpretation: The 95th percentile of the Gaussian distribution of whole blood lead concentration in
a population of unexposed adults is 25 mcg/dL in
children or >45 mcg/dL in adults. The Occupational Safety and Health Administration has published the
following standards for employees working in industry: -Employees with a single whole blood lead
result >60 mcg/dL must be removed from workplace exposure. -Employees with whole blood lead
levels >50 mcg/dL averaged over 3 blood samplings must be removed from workplace exposure. -An
employee may not return to work in a lead exposure environment until their whole blood lead level is
or =7 years: 0-9 mcg/dL
Critical values
Pediatrics (< or =15 years): > or =20 mcg/dL
Adults (> or =16 years): > or =70 mcg/dL
Clinical References: 1. Occupational Safety and Health Administration: OSHA Lead Standard -
Requirements from the General Industry Standards Lead (1910.1025), from 29 CFR 1910.1025, A.M.
Best Safety and Security - 2000. Cited March 2000. Available from URL:
http://www.ambest.com/safety/osha/chap10g.html 2. Rosen JF: Preventing Lead Poisoning in Young
Children. US Public Health Service, Centers for Disease Control, Atlanta, GA, 1991 3. Bellinger D,
Leviton A, Waternaux C, et al: Longitudinal analyses of prenatal and postnatal lead exposure and early
cognitive development. N Engl J Med 1987 Apr 23;316(17):1037-1043 4. Needleman HL, Schell A,
Bellinger D, et al: The long-term effects of exposure to low doses of lead in childhood. An 11-year
follow-up report. N Engl J Med 1990 Jan 11;322(2):83-88 5. Nixon DE, Moyer TP, Windebank AJ, et
al: Lack of correlation of low level sof whole blood and serum lead in humans: an experimental
evaluation in animals. In Trace Substances in Envrionmental Health XIX. Proceedings of the University
of Missouri's 19th Annual Conference on Trace Substances in Environmental Health, Columbia, MO,
June 3-6, 1985, pp248-256
Lead, Hair
8495
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