7. METALSApproximately 35 metals are of major concern in regard to occupational exposure. Two thirds of them can cause health hazards if not properly handled and may result in well-defined toxic effects in humans. Some metals are not poisonous in small amounts and may, on the contrary, be necessary for good health. On the other hands, some metals, even in small doses, may cause both immediate and chronic poisoning. Damage may involve disturbances of the blood composition or nervous system, or injury to the liver or kidneys. Long-term exposure to certain metal compounds may cause cancer. Allergic reactions may result from repeated long term contact with some metals and metal compounds.
Mercury, lead, cadmium, nickel, chromium, manganese, arsenic, antimony, zinc, copper, cobalt, vanadium and beryllium are used in industry and are known to cause adverse health effects both as the metal and as metallic compounds.
As a rule, acute poisoning results from inhalation of dust, fume or vapour dispersed in the workplace air. Intake of some metals and their compounds is also possible through the skin.
Mercury is absorbed into the body through the inhalation of fumes. Mercury compounds may also pass through the skin. Mercury causes damage to the nervous system. In the environment, mercury is converted to an organic compound, methylmercury, which accumulates, for example, in fish and passes through the food chain to humans. This compound is known to affect unborn babies. Mercury compounds are present in chlorine production and mining and are used, for example, in tanner's mordant, pickling baths and pesticides.
Cadmium is a component of some solder metals and baths used for electroplating. It is used in Ni-Cd batteries. PVC plastics may contain cadmium stearate as a heat stabilizer. Many pigments contain cadmium compounds, often to make yellow or red colours.
The human body lacks the ability to expel this metal from its system. Practically all the cadmium taken in during the lifetime is stored in the kidneys, which gradually results inreduced kidney function.
Cadmium and its compounds are environmental and marine pollutants. Many countries have banned or severely restricted certain uses of cadmium compounds.
Nickel is used in the production of a wide range of alloys, including stainless steel. Nickel is a sensitizing material; nickel allergy is fairly common where nickel or its compounds are worked with, for example, when plating with nickel. Some nickel compounds also cause cancer.
Chromium, especially in salt and as chromic acid, is widely used in different types of industry. Chromium is part of stainless steel and several other alloys, it is used in electroplating various metal parts, from electrical equipment to car parts. Chromium compounds are used in dyeing of textiles and they can be present in small amounts in concrete. Chromium compounds may cause cancer and are sensitizing.
Manganese is a component of many alloys, and is also used in making steel. Dust and smoke from mines and smelting plants contain this metal and its compounds. It is also a component of welding electrodes which likewise releases dust and fumes. Manganese exposure weakens the defense system of the body against infections and may seriously damage the nervous system.
Zinc and copper are often components of the fumes causing `metal fever'.
Lead is a bluish grey, heavy metal. It is very soft and very resistant to corrosion. Lead pipes used as drains from the baths during the times of ancient Roman emperors are still in service. The melting point for lead is fairly low for a metal: 3270 °C, and it starts to evaporate above 500 °C. These temperatures are reached in welding, grinding or soldering, which are the working methods applied to metals.
Lead is the most widely used metal after iron. About 2.5 million tons of lead are produced yearly in the world. Most of this lead goes into battery production and most of the remainder is used in cable covering, plumbing, ammunition and in the manufacture of alkyllead compounds, used as fuel additives.
Lead scrap handling is common and lead is extensively recycled, for example, from batteries. Lead is a component of galvanizing materials and of many alloys such as solder, brass and bearing metals. The metal is a good noise and sound absorber, and it is used as radiation shields around X-ray equipment.
Lead compounds have been widely used as pigments in paints, although recently their use has been drastically curtailed to reduce the health hazards. Most commonly it is found in lead paint for protecting metal surfaces.
The polyvinyl plastic industry uses lead compounds as stabilizers, and the ceramic industry uses lead oxides and silicates in porcelain and enamelled tiles. Lead oxide is used to produce crystal glass and lead arsenate is a pesticide.
Environmental concern over the adverse effects of lead has resulted in programmes to reduce or eliminate lead from fuel.
Lead compounds are marine pollutants.
Lead compounds may be divided in two chemical categories:
Care must be exercised when handling lead or its compounds as they are cumulative poisons. This means that exposure to lead and its compounds causes a 'lead burden'. The normal lead burden is the amount of lead derived from the environment (air, water, soil) mainly through food. Working conditions may add to the total lead burden.
The Threshold Limit Value (TLV) for lead compounds, such as lead acetate, lead arsenate, lead carbonate and lead phosphate, is 0.15 mg/m3. The TLV is 0.05 for lead chromate and tetraethyl lead. For total dust, lead metal and most of its inorganic compounds, the TLV is 0.1 mg/m3 in some countries.
In the EU countries lead compounds are classified either as harmful: Xn, or toxic: T.
Health effects of lead
Lead can be absorbed into the body through the respiratory tract or from the stomach. Some lead compounds penetrate the skin, such as tetraethyl lead, which is used in fuel as an antiknock agent. About one third of inhaled lead fumes is absorbed. One tenth of ingested lead is absorbed.
Once lead has entered the human body it causes adverse effects. It combines with red blood cells causing anaemia. Lead also settles in bones taking the place of calcium. It can be found in the liver and kidneys.
Lead affects the nervous system, including the brain.
Lead may pass through the placenta from mother to the unborn baby and it is found in milk if the mother has been exposed.
Children are especially sensitive to lead.
Lead is excreted only very slowly. The kidneys are the main route but sweat, nails and hair also play a part in eliminating lead from the body.
Inhalation of dust, vapour, or smoke containing lead or inorganic lead compounds results to lead poisoning. Early signs of poisoning are stomachache, loss of appetite, fatigue and sleeplessness. If the exposure continues, the lead starts to accumulate because of the very slow excretion. Other symptoms may appear: headaches, memory failures, changes in the blood, muscle and joint pain. The nervous system may be affected, resulting in the following various problems: shaky hands, muscular weakness and, at the worst, paralysis, which often begins in the muscles of forearms and hands.
Organic lead compounds have higher acute toxicity than inorganic lead, and they may penetrate the skin as well as enter the body through inhalation.
Prevention of occupational exposure
Lead is in most cases present in the air of the workplace as dust or fumes. Preventive engineering solutions are related to the formation, moving and collecting of the dusts and fumes. In some cases substitution is possible, for example, in the pottery industry certain lead compounds may be replacedwith lead polysilicates. In many countries lead-containing paints are banned or restricted for certain uses.
Not only does a Code of Practice guide the use of lead and its compounds in industry and society; laws have been enacted in many countries to protect the worker, since lead poisoning used to be one of the most common occupational diseases.
These laws may set limits to the exposure and require monitoring of the level of lead concentration in the air of the workplace and medical surveillance of exposed persons. It may be a requirement to keep records of results in order to be able to assess preventive methods and exposure to lead. The frequency of monitoring and medical check-ups vary depending on the exposure. The medical surveillance should continue from before the lead exposure begins until after the exposure to lead ceases. Duties for preventive action have been defined for both workers and for employers.
To maintain an adequate hygienic level, the following basic measures should be considered:
Worker and/or their representatives should have access to the results of lead-in-air measurements and the statistical results of medical findings.
ARBETARSKYDDSNÄMNDEN, Kemiska hälsorisker, Gummessons Tryckeri, Falköping, Sweden, 1990
BAKAR CHE MAN A. and GOLD D., Safety and Health in the use of Chemicals at Work: A training manual, ILO, Geneva, 1993
ILO, International Labour Organisation, Code of Practice: Safety in the Use of Chemicals at Work, Geneva 1993
ILO, International Labour Organisation, Safety and Health in the use of Agrochemicals: A Guide, Geneva, 1991
TUC, Trade Union Congress, Hazards at Work, TUC Guide to health and safety, Macdermott and Chant Ltd., London, 1988
IPCS, International Programme on Chemical Safety, Environmental Health Criteria Series, No.3 Lead, Geneva 1977
IPCS, International Programme on Chemical Safety, and CEC, Commission of the European Communities, International Chemical Safety Cards, ICSC#0052
82/605/EEC Council Directive of 28 July 1982 on the protection of workers from the risks related to the exposure to the metallic lead and its ionic compounds at work