Heavy metal toxicity

What are the 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.

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

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 manufacturing
• Fuel additives, PVC plastics, crystal glass production, pencils and pesticides

Mercury

• Mining operations, chloralkali plants, paper industries
• Thermometers, vaccines
• Skin lightening products

Cadmium

• Mining and smelting of lead and zinc
• Nickel-cadmium batteries, PVC plastics, paint pigments
• Insecticides, fungicides, sludge and fertilisers

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 the regular hand-to-mouth activity of small children who play in contaminated soils or eat/chew on objects that are not food, such as 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 an exposure causes acute toxicity or chronic and subtle effects.

Signs and symptoms of acute toxicity

• Severe, rapid in onset
• Cramping, nausea, vomiting, pain
• Breathing difficulties
• Sweating
• Headaches
• Convulsions
• Skin rash

Signs and symptoms of chronic exposure

• 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.