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Heavy metal toxicity

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.

Industrial exposure is a common route of exposure for adults. A number of heavy metals are used or produced as a by-product in many agricultural, manufacturing and pharmaceutical processes.

Heavy metal	Potential sources for exposure
Arsenic	Smelting process of copper, zinc and lead Manufacture of chemicals and glass Pesticides, fungicides, paints, rat poison, wood preservatives
Lead	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
Mercury	Mining operations, chloralkali plants, paper industries Thermometers, dental amalgam (fillings), vaccines
Cadmium	Mining and smelting of lead and zinc Nickel-cadmium batteries, PVC plastics, paint pigments Insecticides, fungicides, sludge and fertilizers
Silver	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
Iron	Dietary iron supplements Drinking water, iron pipes and cookware
Gold	Gold therapy for rheumatoid arthritis

The most common route of exposure to heavy metals in children is through accidental ingestion. Toxic levels of heavy metals can develop through normal hand-to-mouth activity of small children who play in contaminated soils or eat/chew on objects that are not food, e.g. bark chips, dirt or painted objects.

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 toxicity	Signs 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.

Related information

References:

Book: Textbook of Dermatology. Ed Rook A, Wilkinson DS, Ebling FJB, Champion RH, Burton JL. Fourth edition. Blackwell Scientific Publications.

On DermNet NZ:

Arsenic – see chronic arsenic poisoning
Silver – see argyria
Gold – see chrysiasis
Mercury – see acrodynia

Other websites:

Life Extension: Heavy Metal Toxicity

Books about skin diseases:

See the DermNet NZ bookstore

Author: Vanessa Ngan, staff writer