Heavy metal toxicity

Author: Vanessa Ngan, Staff Writer, 2005.

What are heavy metals?

Heavy metals are chemical elements that are commonly found in our environment. Without realising it all people are exposed to heavy metals on a daily basis. However, the quantities that we inhale, ingest or come into contact with the skin are so small that they are usually harmless. In fact, small amounts of some heavy metals in our diet are essential to good health. These are referred to as trace elements and include iron, copper, manganese, zinc, plus others, which are commonly found naturally in fruits and vegetables.

Toxic heavy metals and routes of exposure

Toxic heavy metals are heavy metals that become poisonous to the body when they are not metabolised or excreted and so accumulate in organs and tissues. They enter the human body through food, water, air, or absorption through the skin. Routes of exposure are described below.

Heavy metalPotential sources for exposure
  • Smelting process of copper, zinc and lead
  • Manufacture of chemicals and glass
  • Pesticides, fungicides, paints, rat poison, wood preservatives
  • Pipes, drains and soldering materials
  • Old lead-based painted houses and furniture that has started to flake, chip, chalk and dust
  • Battery manufacture
  • Fuel additives, PVC plastics, crystal glass production, pencils and pesticides
  • Mining operations, chloralkali plants, paper industries
  • Thermometers, dental amalgam (fillings), vaccines
  • Mining and smelting of lead and zinc
  • Nickel-cadmium batteries, PVC plastics, paint pigments
  • Insecticides, fungicides, sludge and fertilizers
  • Silver mining, refining, silverware and metal alloy manufacturing, metallic films on glass electroplating solutions, photographic processing
  • Colloidal silver dietary supplements, silver salts in nasal/eye drops, irrigations and wound dressings
  • Dietary iron supplements
  • Drinking water, iron pipes and cookware

Signs and symptoms of heavy metal toxicity

Signs and symptoms of toxicity depend on the heavy metal involved and whether exposure causes acute toxicity or chronic and subtle effects.

Signs and symptoms of acute toxicitySigns and symptoms of chronic exposure
  • Severe, rapid in onset
  • Cramping, nausea, vomiting, pain
  • Breathing difficulties
  • Sweating
  • Headaches
  • Convulsions
  • Skin rash
  • Develop slowly over months or years
  • Skin changes
  • Impaired cognitive, motor and language skills
  • Nausea, lethargy, malaise
  • Insomnia
  • Emotional instability

The heavy metals that cause the most significant skin changes and are discussed in more detail include arsenic, silver, gold and mercury.

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