Module 3: Toxicology - Section 12: Heavy Metals
OHM12.X: Introduction
 

INTRODUCTION:

Metal and related compounds have been part of industrial settings and the environment for millenia. The risks due to ingestion or inhalation of these metals have been well documented. 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. Despite our extensive knowledge about various metals, industrial and environmental exposures continue to produce significant pathology among people 1.

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

There are three primary types of elements based on chemical and physical parameters:

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 following is a table indicating toxicity of metals:

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, (Beryllium causes lung fibrosis and Cancer)
GROUP IIB (Zn, Cd, Hg) Form strong covalent bonds – affinity for thiol, (-SH), groups MERCURY & CADMIUM are persistent toxicants
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 is an exception because of radioactivity
GROUP IVA (Ge, Sn, Pb) GERMANIUM & TIN have low solubility and toxicity. ORGANIC FORMS CAUSE NEUROTOXICITY.

LEAD – Both INORGANIC & ORGANIC FORMS HIGHLY TOXIC.
GROUP IVB (Ti, Zr, Hf)  
GROUP V (ARSENIC [As]) As2O5 metabolized to more toxic As2O3.
Fevers, colic, hepatitis, progressive neuropathy, anemia, nephropathy.
Cancers of skin, lung and liver

REFERENCES:

  1. L Rosenstock, M Cullen. Textbook of Occupational and Environmental Medicine. Chapter 30.
  2. http://www.osha.gov/SLTC/metalsheavy/
  3. http://www.emedicine.com/EMERG/topic237.htm
  4. http://www.lenntech.com/heavy-metals.htm



Creative Commons License
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.
Disclaimer note: Some resources and descriptions may be out-dated. For suggested updates and feedback, please contact healthoer@uct.ac.za.