Heavy metals is a general term covering potentially toxic metals such as arsenic, cadmium, chromium, copper, lead, nickel and zinc. Heavy metals may be discharged into the environment and be found as suspended particulate matter in the atmosphere, in stream and marine sediments, or dissolved in water. There are 35 metals of major concern with regard to occupational exposure. About 20 of these may constitute occupational health hazards if not properly handled and may lead to toxic effects in humans. Toxicity may be either acute or chronic.
Acute toxic effects from metals are usually the result of the inhalation of air or the ingestion of liquids containing the metals in very high concentrations. Dangerously high concentrations of metals in workroom air may occur after industrial accidents (such as explosions, sudden leakage of metal fumes from normally closed containers, sudden failure in ventilation systems). Inhalation of high concentrations of metals is irritating and may cause severe damage to the respiratory tract. Fatalities may occur either immediately after exposure or up to several weeks later. Ingestion of high concentrations of metals may take also place through their leakage from containers and pipes into beverages. For example, acute intoxication has often occurred from consumption of home-brewed alcoholic drinks distilled in lead radiators or copper pans. The symptoms following the ingestion of excessive amounts of metals are those of food poisoning, with nausea, vomiting, abdominal pains and, in certain cases, diarrhoea.
The effects of chronic occupational exposure to metals are the most frequent, and are mainly derived from industrial activity. The toxicity of some metals, such as lead, has been known to man for centuries, and may lead to lead paralysis and colic. The inhalation of mercury vapour in mining and in the felt hat industry frequently causes severe central nervous-system symptoms; and long-term exposure to cadmium in workroom air causes pulmonary emphysema and kidney damage with proteinurea.
Exposure to heavy metals has been linked with developmental retardation, various cancers, and kidney damage. Exposure to high levels of mercury, gold and lead has also been associated with the development of auto-immunity, in which the immune system starts to attack its own cells, mistaking them for foreign invaders (Grover-Kerkvliet 1995). Several studies have shown that lead exposures can significantly reduce the IQ of children (Goyer 1996). In some countries, heavy metal emissions are falling as a result of the removal of lead from petrol, improvements in wastewater treatment and incinerators, and improved industrial technologies. Significant further improvements could be achieved if the available technologies were more widely applied (EEA 1998).
Regarding the effects of exposure in the general environment, most problems stem from cadmium, mercury, arsenic and lead. Some worldwide examples are the following: In Japan, cadmium has given rise to the Itai-Itai (or ouch-ouch) disease in hundreds of people. Methylmercury poisoning resulting from the consumption of contaminated fish also caused the Minamata disease in Japan, when methylmercury accumulated in the brains of people who ate contaminated fish caused irreversible damage to the central nervous system with associated ataxia, paraesthesia and decreased visual field; furthermore, a number of children having severe cerebral palsy-like brain damage were delivered by mercury-exposed mothers. In Iraq poisoning was causing by eating seed treated with methylmercury; about 6,000 people were hospitalized, and there were some 500 fatalities.
Lead poisoning in children is a serious world-wide problem. In addition to lead in food and air, children are exposed to lead in contaminated dust and soil, and from the consumption of paints containing lead (pica). It has been estimated that hundreds of thousands of children in the USA are in peril of subclinical lead poisoning.
Arsenic in drinking water has caused severe health problems in Asia and in South and North America. Consumption of water containing arsenic may give rise to vascular changes, hyperpigmentation and keratosis of the skin, and skin cancer.
In 1992, the air over southern Poland contained 5 times the permissible level of cadmium, 8 times the acceptable level of lead and 4 times the acceptable level of sulphur dioxide. So much heavy metal poison has accumulated in the soil that it is not advised to eat food grown in the area.
Heavy metals may be released suddenly into the environment by a breach in toxic waste stores. In 1998, a waste storage lagoon burst at the Los Frailes zinc mine in Spain, sending a toxic wave down the Guadiamar river towards the Doñana National Park. Coastal toxic dump sites could become hazardous to surrounding communities during a storm surge or if sea level were to rise.