Module 3: Toxicology - Section 11: Lead
TOX 11.2: Introduction To Toxicity Of Metals

Introduction

Metal and related compounds have been part of industrial settings and the environment for millenia. The risks from ingestion or inhalation of these metals have been well documented. (Skin absorption is less important). Despite our extensive knowledge about various metals, industrial and environmental exposures continue to constitute a significant hazard.

In the periodic table of elements, there are three primary types of elements based on chemical and physical characteristics.

Metals are intrinsically stable and retain their identity despite physical and chemical transformation. Almost all metals can be measured in some biological fluid or system.

In general the metals are elements from the middle or left hand side of the periodic table (typically cationic). A metal may be found in its elemental form, as an inorganic salt or organically bound, with differing toxicities.

Some metals form complexes with electron donor groups on ligands consisting of anionic or neutral organic or inorganic species. There are inorganic forms of most metals strongly bound by protein and biological tissue.

The table below lists the metals and their general toxicity features.

Group Toxicity
GROUP IA (Li, Na, K, Rb, Cs) Essential elements
GROUP IB (Cu, Ag, Au) Low toxicity
GROUP IIA (Be, Mg, Ca, Sr, Ba) Low toxicity; Exception: beryllium - lung fibrosis and ?cancer
GROUP IIB (Zn, Cd, Hg) Form strong covalent bonds - affinity for thiol (-SH) groups; Mercury and cadmium are heavy metals: highly toxic and persistent in nature; Zinc fumes cause metal fume fever.
GROUP IIIA (Al, In, Tl) Uncommon causes of toxicity; Target organs include, liver, brain and lung.
GROUP IIIB (Sc, Y, and Lanthanides) Low solubility; Thorium hazardous from radioactivity
GROUP IVA (Ge, Sn, Pb) Germanium (Ge) and tin (Sn) have low solubility and toxicity, but organic form are neurotoxic. Lead (Pb) - inorganic and organic forms toxic.
GROUP IVB (Ti, Zr, Hf) Low solubility and toxicity - found in deodorants and hair sprays.Zirconium can cause hypersensitivity of lungs.
GROUP V (As) Arsenic (As): heavy metal. Highly toxic: multisystem disorders including cancer.

Reference:

  1. L. Rosenstock, M Cullen. Textbook of Occupational and Environmental Medicine, Ch. 30.



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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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