MRS M recently called me, very concerned about the welfare of her brother - a factory worker who lives overseas. "Doctor he, has been sick for some time now, going to different doctors. Now they say that he may be suffering from heavy metal poisoning. They are not too sure what is causing this, but they are running more tests. What is this all about ?"

Heavy metal toxicity represents a common medical condition. If unrecognised or inappropriately treated, it can result in significant morbidity and even death.

Vegetables such as brocolli (left) and spinach are good sources of iron, one of the nutritionally essential metal for a healthy life.

Occupational exposure to heavy metals has accounted for the vast majority of poisonings throughout human history. Hippocrates described abdominal colic in a man who extracted metals, and the pernicious effects of arsenic and mercury among smelters were known even to Theophrastus of Erebus (370-287 BC).

There are 35 metals that concern us because of occupational or residential exposure; 23 of these are the heavy metals - antimony, arsenic, bismuth, cadmium, cerium, chromium, cobalt, copper, gallium, gold, iron, lead, manganese, mercury, nickel, platinum, silver, tellurium, thallium, tin, uranium, vanadium, and zinc.

Heavy metals are chemical elements with a specific gravity that is at least five times the specific gravity of water. Specific gravity is a measure of density of a given amount of a solid substance when it is compared to an equal amount of water. The specific gravity of water is 1 at 4°C .

Heavy metals are stable elements - they cannot be metabolised by the body and are bio-accumulative, that is, they are passed up the food chain to humans. In general, they have no function in the body and can be highly toxic.

Beneficial heavy metals

In small quantities, certain heavy metals (chromium, copper, cobalt, iron, and zinc) are nutritionally essential for a healthy life. They are referred to as the trace elements These elements, or some form of them, are commonly found naturally in fruits and vegetables, and in commercially available multivitamin products. Iron, for example, prevents anaemia, and zinc is a co-factor in over one hundred enzyme reactions.

Heavy metals are also common in the manufacture of pesticides, batteries, alloys, electroplated metal parts, textile dyes and steel. Many of these products are found in our households and enhance the quality of our lives when properly utilised.

Toxic heavy metals

Heavy metals become toxic when they accumulate in the soft tissues of the body. Routes of exposure include inhalation, skin or eye contact, and ingestion. Persons working in agricultural, manufacturing, pharmaceutical, industrial, or residential settings are susceptible to heavy metal toxicity. Industrial exposure accounts for a common route of exposure for adults, while ingestion is the most common route of exposure in children .

Toxic effects from chronic exposure to heavy metals are far more common than acute poisonings. Chronic exposure may lead to a variety of conditions depending on the route of exposure and the metabolism and storage of the specific element in question.

Acute toxicity is usually from a sudden or unexpected exposure to a high level of the heavy metal (for example from inadequate safety precautions, or an accidental spill or release of toxic material in a laboratory, industrial, or transportation setting). Symptoms indicative of acute toxicity are usually severe, rapid in onset and associated with a known exposure or ingestion. They include nausea, vomiting, pain, sweating, headaches, difficult breathing, impaired cognitive skills and convulsions.

Chronic toxicity results from repeated or continuous exposure, leading to an accumulation of the toxic substance in the body. Chronic exposure may result from contaminated food, air, water, or dust; living near a hazardous waste site; spending time in areas with deteriorating lead paint or from participating in hobbies that use lead paint or solder.

Symptoms of chronic toxicity - impaired cognitive, motor, and language skills, learning difficulties, nervousness, insomnia, nausea and lethargy - are often similar to many common conditions and may not be readily recognised. These symptoms often develop slowly over months or even years.
Arsenic, lead, cadmium and mercury are the metals most commonly implicated in acute and/or chronic heavy metal toxicity.

Arsenic

Arsenic is well known as a poison used in homicidal and suicidal attempts. Napoleon may have accidentally succumbed to its effects. His exposure is thought to have been due to a greenish pigment used in the decorative wallpaper hung in his room on St Helena during his exile.

Arsenic is found in nature at low levels. It is mostly in compounds with oxygen, chlorine, and sulfur (inorganic arsenic compounds). Arsenic in plants and animals combines with carbon and hydrogen (organic arsenic). Organic arsenic is usually less harmful than inorganic arsenic. Most arsenic compounds have no smell or special taste.

Arsenic is released into the environment by the smelting process of copper, zinc, and lead, as well as by the manufacturing of chemicals and glasses. It may also be found in water supplies worldwide, leading to exposure of shellfish, cod, and haddock. Other sources are paints, rat poisons, fungicides, and wood preservatives. Body targets are the blood, kidneys, and central nervous, digestive, and skin systems.

The metal was the primary compound in the spray known as Lewisite that was used by the British during trench warfare in World War I. Exposure produced severe swelling of the eyelids, gastrointestinal irritation and both central and peripheral neuropathies. The first antedote to heavy metal poisoning, British Anti-Lewisite (dimercaprol), and the basis for chelation therapy was developed by the Germans during World War II in anticipation of a reinitiation of gas warfare.

Lead

Industrial decisions, such as the addition of lead to paints, dyes, and gasoline, have created an epidemic of lead poisonings.
Lead accounts for most of the cases of paediatric heavy metal poisoning.

Exposure risk is higher in deteriorating inner-city neighbourhoods; however, this disease occurs in all social and economic classes. Lead is a very soft metal and was used in pipes, drains, and soldering materials for many years. In fact, many older homes still contain lead in painted surfaces, leading to chronic exposure from weathering, flaking, chalking, and dust. (Since 1977, paints produced in the United States do not contain lead.)
Lead is used in the manufacture of batteries, cable coverings, ammunition, and fuel additives.

It is found in PVC plastics, x-ray shielding, crystal glass production, pencils, and pesticides. Target organs are the bones, brain, blood, kidneys, and thyroid gland.

Cadmium

Cadmium is a by-product of the mining and smelting of lead and zinc. It is found in nickel-cadmium batteries, cigarettes, PVC plastics, and paint pigments. Cadmium can be found in soils because insecticides, fungicides, sludge, and commercial fertilisers that use cadmium are used in agriculture.

This heavy metal may be found in reservoirs containing shellfish. Lesser-known sources of cadmium exposure are dental alloys, electroplating, motor oil, and exhaust. Targets in the body are the liver, placenta, kidneys, lungs, brain, and bones.

Acute exposure to cadmium generally occurs in the workplace, particularly in the manufacturing processes of batteries and colour pigments used in paint and plastics. Symptoms of acute cadmium exposure are nausea and vomiting.

Symptoms of chronic exposure to cadmium include hair loss, anaemia, arthritis, learning disorders, migraines, growth impairment, osteoporosis, loss of taste and smell, chronic obstructive lung disease and cardiovascular disease.
We will continue with this topic next week.

Dr Jacqueline E Campbell is a family physician in private practice. E-mail drjcampbell14@yahoo.com.

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