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| Module 3: Toxicology - Section 12: Heavy Metals |
| OHM12.X: Lead - Part 3 |
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| Module 3: Toxicology - Section 12: Heavy Metals |
| OHM12.X: Lead - Part 3 |
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Tetraethyl (TEL) and tetramethyl (TML) are added to gasoline as antiknock agents. Workers in the petroleum industry and those repairing and cleaning storage tanks. TML and TEL are hazardous because they are absorbed through the skin and the vapors are inhaled. They are lipid soluble and are easily transported to the brain and bone. They do not appreciably affect haeme synthesis.
Blood lead determination is the most sensitive measure of lead exposure for relatively recent exposure. Free erythrocyte protoporphyrin levels stay elevated for several weeks after clearance of one acute dosage and prolong the diagnostic window for detection after an exposure. Flat plate abdominal X Ray may confirm recent ingestion and is particularly useful in children. Similarly X Ray of the long bones in children may reveal sclerosis of the metaphyseal growth plates from lead deposition. Urinary lead excretion is a reliable indicator of recent exposure and post chelation urinary lead excretion a good indication of body burden.
Poisoning usually begins with vague symptoms of fatigue and nervousness. Other symptoms include insomnia, troubled dreams, anorexia and hypotension. Colic and alternating constipation diarrhea are commonly seen particularly in children. In severe poisoning CNS abnormalities are profound and present as a spectrum from low-grade malaise, memory loss and irritability to seizures and coma.
Immediate removal from exposure is mandatory. Chelating agents can be used but should be provided in hospital settings. The standard is chelation with intravenous calcium EDTA (1g every 8 hours) with a saline infusion for 2 to 3 days. Monitor patients for hypocalcemia, oliguria and hematuria. Subsequently oral penicillamine maybe used to continue chelation. One needs to monitor for side effects. Periodic assessment of bllod lead and urinary excretion may be useful during chelation to assess body burden and efficacy. During chelation urinary lead excretion will typically increase dramatically and blood lead decrease gradually. As the lead being excreted is being mobilized from the storage depot in bone there may be a rebound elevation in blood lead noted one to two weeks after chelation is completed. In such cases several rounds of chelation therapy may be needed to deplete a chronically elevated body burden sequestered in bone. The decision to chelate is made based upon the severity of the presentation, evidence of target organ injury , the age of the subject, (children are hypersusceptible to the neurotoxic effects of lead), the blood lead level and the recency of exposure. The more recent the exposure the greater the efficacy of chelation. In some instances the only treatment required maybe supportive with attention to fluid and electrolyte balance. Oral DMSA, dimercaptosuccinic acid is proving to be a safer oral alternative for chelation of lead and is administered 30 mg/kg/d in three divided doses ×5 days and maintained at 20 mg/kg/d in two divided doses for 112 additional days.
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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