Module 3: Toxicology - Section 12: Heavy Metals |
OHM12.X: Lead - Part 2 |
Lead inhibits amino-levulinic acid dehydrogenase (ALAD) and ferrochelatase which are enzymes in the biosynthetic pathway of haemeglobin. Lead competes with calcium in several of the biological systems including cellular respiration. Lead also affects both deoxyribonucleic acid and ribonucleic acid.
Blood Lead (PbB): Blood lead is the best indicator of the concentration of lead in soft tissues and is regarded as the best indicator of recent exposure. It has the greatest meaning under steady state but does not necessarily correlate with the total body burden of lead and is thus a crude index of an individuals' true exposure. When a worker is removed from exposure PbB decreases with a half life of 35 days, but it may not return to normal because of the release of lead from tissue deposits. It is not a useful indicator of past exposure.
Urinary Lead (PbU): This reflects the amount of lead recently absorbed. It is influenced by renal excretion function and fluid intake. Used in industry because it does not require the removal of blood.
Urinary excretion of lead after administration of a chelating agent: In workers currently exposed to lead the urinary lead after chelation correlates with the urinary lead after chelation correlates with PbB. Urinary chelation may be used to confirm past exposure to lead among people currently exposed. A Ca EDTA provocative challenge test may be performed by administering 1 gram Ca EDTA I.V. and collecting a 212 hour urine for lead excretion. Excretion of over 500 micrograms of lead is confirmative of an elevated body burden.
Lead in hair: This can be used as a method of evaluating the body burden of lead. It has limited use because of the difficulty of differentiating between lead incorporated into the hair and lead which is absorbed onto the hair surface.
Postgraduate Diploma in Occupational Health (DOH) - Modules 3: Occupational Medicine & Toxicology (Basic) by Profs Mohamed Jeebhay and Rodney Ehrlich, Health Sciences UCT is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.5 South Africa License. Major contributors: Mohamed Jeebhay, Rodney Ehrlich, Jonny Myers, Leslie London, Sophie Kisting, Rajen Naidoo, Saloshni Naidoo. Source available from here. For any updates to the material, or more permissions beyond the scope of this license, please email healthoer@uct.ac.za or visit www.healthedu.uct.ac.za.
Last updated Jan 2007.
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