CHEMICAL SAFETY TRAINING MODULES

PART VII: METALS

METALS

Approximately 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 in reduced kidney function.

Cadmium and its compounds are environmental and marine pollutants. Many countries have banned or severely restricted certain uses of cadmium compounds.

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

1. Properties

Lead is a bluish grey, heavy metal. It is 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: 327^oC, and it starts to evaporate above 500^oC. Also some lead compounds, such as lead carbonate, lead nitrate and lead oxide (red), decompose at those temperatures releasing lead fumes. These temperatures are reached in welding, grinding or soldering.

Lead compounds may be divided in two chemical categories:

• inorganic; such as lead nitrate, lead oxide and lead sulphate
• organic; such as tetraethyl lead.

The industrially important lead salts are solid, most of them are insoluble into water. Lead acetate and lead nitrate are water soluble, chlorate and chloride reasonable soluble in cold water, lead sulphide and lead oxides are poorly soluble.

Important organic lead compounds, tetraethyl lead and tetramethyl lead, used as fuel additives, are flammable liquids which evaporate easily at room temperature.

In the nature lead is found in sulphide minerals.

2. 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. Exposure to lead at levels without apparent adverse effects could result to permanent mental impairment.

Inhalation of dust, vapour, or smoke containing lead or inorganic lead compounds results to lead poisoning. Early signs of poisoning are stomach-ache, 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.

Lead is excreted only very slowly. The kidneys are the main route. Sweat, nails and hair also play a part in eliminating lead from the body.

Organic lead compounds have higher acute toxicity than inorganic lead, and they may penetrate the skin as well as enter the body through inhalation.

3. Occupational use and exposure

Lead is the most widely used metal after iron. About 3 million tons of lead are in consumption yearly in the world. The largest user of lead is the battery industry. Lead is also added to many alloys; only iron has a wider application in alloys. Lead is used in brass, bronze, soldering metal, bearings. It is present in cable sheaths, plumbing, ammunition and in the manufacture of alkyllead compounds, used as petrol additives.

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. A TV display, the glass in the cathode ray tube, contains about 2 kg of lead in the form of lead silicates. An ordinary light bulb contains up to 1 g of lead in its solders and 0.5-1 g of lead silicates in the glass. Lead oxide is used to produce crystal glass and lead arsenate is a pesticide.

Lead scrap handling is common and lead is extensively recycled, for example, from batteries.

Occupational exposure to lead and its compounds is possible in following activities:

• mining and preparation of ore
• melting, casting, flame cutting of lead and lead alloys
• non-ferrous metal foundries, manufacturing of gun metal and lead containing brass and bronze
• battery industry: production, collection and recycling
• manufacturing, using and removing (sand-blasting) lead paint
• plastic production (PVC using lead stearate as stabilizer)
• glass and ceramic manufacturing
• soldering and joint filling
• manufacturing of explosives, such as containing lead azide; shot metal
• radiator repair (a lorry radiator contains about 2 kg of lead)
• manufacturing and repair of corrosion resistant reservoirs and tanks
• production, distribution, exposure to exhaust gases of leaded fuel

4. Safety measures and monitoring

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. As dust is an important way of pollution transmission, also to the surroundings, the ways of collection should considered.

In some cases substitution is possible, for example, in the pottery industry certain lead compounds may be replaced with lead polysilicates which are insoluble in water. Soldering with lead-tin alloy can be substituted with other solder materials, such as tin-silver or bismuth-tin alloys. In many countries lead-containing paints are banned or restricted for specified 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:

• no smoking, eating or drinking in polluted areas
• there should be a separated area where workers can eat and drink without risking contamination by lead
• in very hot workplaces where workers are encouraged to drink they should be provided with drinking facilities not contaminated by lead present in the place of work
• workers should be provided with appropriate protective clothing which should not be taken out of the workplace
• working clothing and street clothes should be separated and not kept in the same cupboard.
• adequate washing facilities should be provided and used.

ACGIH (American Conference of Governmental Industrial Hygienist) has approved for lead and its compounds the following Threshold Limit Values: time-weighted average exposure concentrations TWA are set to correspond to an 8 hour working day and a 40-hour working week.

For total dust, lead metal and most of its inorganic compounds, the exposure limit value is 0.1 mg/m³ in some countries.

Table 2. Threshold limit values related to lead

A2 Suspected human carcinogen

A3 Animal carcinogen

Lead level in blood should be monitored where occupational exposure is possible. For the lead level in blood ACGIH gives the figure 50 micrograms lead/100 ml blood as the BEI (Biological Exposure Indices).

The lead level measured from air samples taken in the workplace and the blood samples from the workers does not necessary correspond well. The variations in the dust and fumes might be considerable during the working day/week/month. The intake varies with chemical properties, particle size and structure of lead containing dust, and lead is a 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; 20 micrograms lead/100 ml blood can be considered as a limit for this lead burden. Working conditions add to the total lead burden.

In some countries the monitoring is compulsory and when the limit value of lead content in blood is exceeded that person must be given work which does not involve lead exposure.

Worker and/or their representatives should have access to the results of lead-in-air measurements and the statistical results of medical findings.

In the EU countries lead compounds are classified either as harmful: Xn, or toxic: T.

Lead compounds classified for transport are in Table 2.

5. Waste disposal

In many countries the collection and recycling of lead is organized. About 40% of the lead used in the production is coming from secondary sources (1992, World Bureau of Metal Statistics).

6. Lead in the environment

The atmospheric distribution is the main route of the discharged lead from major emission sources. Most of the lead is deposited close to the source. It is mostly in a poorly soluble form and precipitates out in soil and sediments and organic matter. In contaminated aquatic systems, almost all of the lead is bound to the sediment. It tends to accumulate into those ecosystems where it is deposited.

The pollution from the lead mining, smelting and refining both primary and secondary lead cause contamination of the nearby environment. The contamination can persist for long periods of time.

Combustion of coal, oil and wood, and some industries, such as steel and cement manufacturing add to the emissions of lead to the atmosphere.

Lead from the leaded fuel used in cars is dispersed into the environment which has created contamination of the air, waters and soil. This lead incorporates into the food and water supplies. Environmental concern of the adverse effects has resulted in programmes to eliminate lead from fuel. The substituting anti-knock compounds are widely used in some countries.

Lead compounds are classified as marine pollutants.

Ambient air levels over 10 micrograms in cubic meter of air have been reported in polluted areas whereas levels below 0.2 in cities where leaded petrol is no longer used.

Present levels of lead in water rarely exceed a few micrograms/litre.

Background levels of lead in soil is 10-70 mg/kg of soil, and mean level near roads has been reported to be 138 mg/kg.

CHROMIUM AND CHROMIUM COMPOUNDS

1. Properties

Chromium is a steel grey metal when in a clean, metallic state. It is mined as chromite ore. Globally over 10 million tons of ore consumed annually. Three quarters of this is used for metallurgical purposes; over one tenth goes to the refractory industry and over one tenth into chemical compounds. Chromium metal is a component of hardened steel, stainless steel, and alloys with nickel, titanium, niobium, cobalt, copper and other metals. Chromium content of steels goes from 3% in tool steel to 27% in stainless steel. Important deposits of chromium ore are found in the form of chromite (such as FeCr₂O₄). Serpentine and ultramafic/basic rocks have high chromium content.

The compounds of chromium have very different roles in nature and effects on human health depending on their oxidation state¹. Common compounds in the trivalent oxidation state are chromium(III)oxide and chromic sulphate. The hexavalent form of chromium can be produced from naturally-occurring trivalent chromium minerals. Chromium trioxide, dichromates and chromates are in the hexavalent oxidation state. Water-soluble hexavalent chromium compounds have the greatest industrial applications as a consequence of being strong oxidizers in acidic solutions. For example, chromium trioxide in solution is the principal constituent for chromium plating.

In the hexavalent state chromium also forms coloured insoluble salts; for example, calcium chromate and zinc chromate are used as corrosion inhibitors.

Chromium occurs ubiquitously in nature at low levels. Trivalent chromium is important to human and animal health as a micronutrient. It is also found in plants.

Compounds of chromium in the higher oxidation states occurring in the environment originate almost completely from human activities, such as industrial oxidation of mined chromium and possibly combustion of fossil fuel, wood, etc. These compounds in the hexavalent oxidation state are relatively stable in air. In contact with living organic matter, soil and natural waters they will be reduced to the trivalent oxidation state.

¹ Oxidation state and oxidation level describe the type of chemical compound and give limits to the possible type of chemical reactions

Table 3. Appearance and solubility of some chromium compounds

2. Health effects

Although low levels of chromium compounds are both ubiquitous and essential, high concentrations of chromium are toxic to humans, animals and plants. Very high doses of chromium may be lethal or impair health severely.

Metallic chromium is biologically inert, i.e. it does not cause sensitization. Chromium salts, particularly those in the hexavalent state, are irritant, corrosive, sensitizing and potential or proven carcinogens. In animal tests hexavalent chromium compounds have affected reproduction. Health and environmental effects of chromium compounds in trivalent and hexavalent oxidation states are very different.

Inhalation is the primary route of occupational exposure. The effects depend on the solubility of inhaled compound and the particle size. Particles which have a small diameter (less than 20 micrometers) remain in the air for extended periods and can be transported considerable distances from the source. The size of particle determines also where in the respiratory system adverse effects take place. Large particles deposit in the upper parts of the respiratory tract while medium size particles (1-5 micrometers) penetrate and stay in the lungs.

Skin exposure manifests itself through irritation, corrosion, ulcers and allergic reactions. Ulceration is caused at the sites of chronic exposure by hexavalent chromium compounds. The lesion begins with a painless papule. These `holes' are often on hands, around fingernails, finger joints or sometimes on forearms or feet and are easily ignored until the surface ulcerates. The ulcers are usually circular with a hard edge and firmly adherent crusting. Without treatment it may penetrate deeply into soft tissues. Healing is slow if the treatment is not started at an early stage. Ulceration may also occur in the nose (in the nasal septum) if dust containing chromium compounds is inhaled. Skin sensitization is common in cement production, concrete handling in the construction industry and leather tanning where chromium compounds come into contact with wet skin.

Both solid and solutions of chromium compounds are irritating to the eyes and may cause burns.

Chronic inhalation or skin contact to trivalent and hexavalent chromium compounds may lead to the development of allergic reactions, such as asthma, and other symptoms of respiratory distress. Lung cancer is a confirmed long-term effect of occupational exposure during the production of hexavalent chromium compounds.

Acute exposure due to the ingestion of chromium compounds may lead to toxic effects in the gastrointestinal tract and may damage the kidneys.

3. Occupational use and exposure

Welding of stainless steel releases hexavalent chromium compounds into the breathing zone of the welder. Welders are estimated to make up more than 1% of the workforce in industrialized countries. Hazardous air contaminants related to manual welding, including aerosols and dusts containing chromium, are a significant source of occupational exposure.

Chromium compounds, chromates and dichromates, have various applications in the oxidation of organic and inorganic materials, for example, the oxidation of anthracene to produce anthraquinone. They are used in the purification processes of chemicals, preparation of catalysts and production of pigments. Important inorganic industrial pigments are, for example, molybdate orange, yellow powder of zinc chromate and chromium oxide green. Chromates are used to prevent rust and corrosion, for example, in diesel engines. Chromic acid is used in metal plating to produce a hard corrosion resistant surface. Chromium compound mixed with glass gives an emerald green colour. Chromium compounds are used in tanning chemicals, fungicides and wood preservatives. Production of light-sensitive dichromate celloids for lithography in the printing industry is also an outlet for chromium compounds.

Chromite has a high melting point (2 040^oC) and has good resistance to corrosion caused by acids and bases at elevated temperatures. Chromite and chrome-magnesite are used in bricks and mortars for furnaces in metal refining and glass production.

Exposure to chromium and its compounds can occur in following workplace processes:

• mining of chromite
• production of stainless steels
• welding, thermal cutting, grinding of stainless steels
• electroplating (decorative plating; hard plating against corrosion)
• aluminum anodizing
• manufacture of cars, locomotives, ships, machines
• manufacture of electrotechnical equipment
• manufacture of instruments and fine mechanical equipment
• repair work of equipment made of stainless steel (e.g. in food production)
• production and use of paints containing chromium pigments (colour; anti-corrosion paints)
• leather tanning
• production and handling of cement (chromium as impurity; high temperature cements for aggressive environments)
• chemical manufacture
• glass, clay and stoneware production (pigments containing chromium)
• timber treatment with wood preservatives containing chromium
• water treatment
• drilling mud (chromium lignosulphonates decrease corrosion of drill strings)
• textile dyeing (e.g. sodium dichromate to improve colour fastness)
• photography and photoengraving
• laboratories

4. Safety measures and monitoring

Due to their carcinogenicity, toxicity and corrosive properties, regulations and guidelines are needed to help to assess and limit exposure to hazardous chromium compounds and reduce adverse health effects.

Control of aerosols (dusts and mists) containing chromium compounds has proved to be a very effective way of reducing health hazards. In the chromium plating industry one in four workers had nasal ulcers in the early 1950s. With the introduction of control measures the frequency of this condition dropped to 2 in 393 chromium-exposed workers in 1982.

These control measures may include: closed processes, effective ventilation at the source, protective clothing and respirators. Spills should be cleaned immediately to prevent the dispersion as airborne dust. Wet cleaning methods should be used wherever possible. Vacuum cleaning is a successful method to remove dry deposits of dust.

Choosing a less hazardous process reduces the exposure: the use of MIG (Metal Inert Gas) and TIG (Tungsten Inert Gas) welding instead of manual metal arc welding.

When a respirator is used the following aspects must be considered: the type of chromium compound (trivalent or hexavalent state), airborne concentration of chromium, the level of reducing factor (protection factor) required, and physical demands of the work.

Protective clothing should be used to prevent skin contact with chromium compounds. Skin must be protected against splashes and where dry salts can be picked up by sweat (e.g. in the leather tanning).

Chemically resistant gloves and eye protection are recommended when handling chromium compounds. Paraffin and lanolin creams should be used as an additional barrier protection. Gloves made of Viton (not of polyethylene or natural rubber) are recommended when chromium trioxide is handled. Fully impermeable, chemically resistant protective equipment should be used to prevent accidental exposure in electroplating.

Occupational exposure limits have been established to assess the exposure to various chromium compounds. ACGIH (American Conference of Governmental Industrial Hygienists) has adapted the following limits for chromium compounds (1993-1994). These threshold limit values (time-weighted average exposure concentrations: TWA) are set to correspond to an 8 hour working day and a 40-hour working week.

Table 4. Threshold limit values related to chromium and chromium compounds

In some countries a limit has been established for the concentration of chromium in cement (2 mg chromium/kg) in order to reduce the risk of sensitization in construction work.

Laboratory advice should be sought if chromium levels at work need to be monitored. There are several technical problems, depending on the type chromium compound to be sampled. Air monitoring provides a good indication of the level of exposure. Air monitoring of chromium dusts requires personal sampling. Quick assessment of the airborne concentration of chromium trioxide can be done using a Dräger tube (Chromic acid 0.1/a) or an equivalent device.

Medical supervision may be advisable for persons handling chromium compounds regularly, such as electroplaters.

Biological exposure indices (BEI) can be used to monitor exposure when taking biological samples, such as urine, blood, hair, and measuring the level of the substance or its metabolite. BEIs apply for an 8-hour working day and a 40-hour working week. They are not intended for diagnosis of an occupational illness, but indicate excessive exposure if several samples from a worker taken over a period of time or a majority of the samples from a group of workers (from the same workplace) exceed the BEI. Chromium is measured from urine samples taken at the end of the working week shift. ACGIH has adopted a BEI of 30 microgram/g creatinine for total chromium in urine.

A number of chromium compounds have been assessed into `Classification of dangerous chemicals' list in European Union countries.

United Nations Recommendations for Transport of Dangerous Goods contain specific classification for transport of some chromium compounds:

Table 5. Classification of some chromium compounds for transport

5. Waste disposal

Waste containing chromium cannot as yet be recycled. Such waste cannot be disposed in incinerators, as chromium is oxidized at high temperatures to its most hazardous, hexavalent state.

Waste with dissolved or soluble chromium compounds where chromium may be in the hexavalent state, such as chromates and dichromates, must be treated chemically (to reduce chromium to the trivalent state), precipitated and dried. Waste containing chromium compounds from different sources, such as electroplating baths, eluates and other sources should be collected separately. Treated compacted sludges can be disposed of in an authorized single-purpose dump, special waste dump or refuse dump.

Small spills may be covered with a reducing agent such as sodium thiosulphate and sulphuric acid at pH 2-3. The slurry should be neutralized by transferring it to a large water container adding soda ash. Dispose with large amounts of running cold water. Large spillage may be absorbed to sand before removing by authorized treatment and disposal.

Do not handle spills without proper personal protective equipment.

Waste containing chromium often have also other hazardous components such acids, nickel, solvents of paints, silica, etc. which, without treatment, are equally unsuitable for landfill.

6. Chromium in the environment

Uncontaminated waters contain chromium up to a few micrograms per litre. Although chromium compounds are present in sediments, water and air, wastes from industrial activities containing chromium are more concentrated and harmful to the environment.

Chromium bound to sediments, in rivers, lakes and sea, is biologically inactive. However, organisms living in sediments with elevated contents of chromium have higher concentrations of chromium than those living in the unpolluted sediment areas.

In non-contaminated soil chromium is normally present as insoluble trivalent compounds. Some 30 different types of ores or minerals containing chromium are found in nature. Studies of the landfills have shown that under certain conditions chromium may leak to the groundwater as water-soluble hexavalent chromium compounds. This is the case if the waste also contains manganese(IV) compounds, which are capable of converting a part of the insoluble chromium(III) compounds to soluble chromium(VI) compounds.

Urban air contains an average of 30 nanograms chromium in a cubic meter of air.

NICKEL AND NICKEL COMPOUNDS

1. Properties

Nickel is a common substance, present in air, water, soil and living organisms. Nickel ore deposits of commercial interest exist as nickel sulphide minerals, such as pentlandite and pyrrhotite, and laterites. Meteorites contain iron alloyed with nickel (5% to 50%) which can be used to identify them from the surrounding soil. Nickel metal is silver-white, hard, malleable, ferromagnetic, with high thermal and electrical conductivity. Nickel and its alloys are resistant to the corrosive action of alkalis and salts, to wet and dry gases and many acids. Dilute oxidizing acids, such as dilute nitric acid solution, dissolve nickel.

Table 6. Solubility of some nickel compounds

2. Health effects

Nickel is present in human tissues normally as a trace element in small amounts. The exposure to high levels of nickel increases the amount significantly. The important routes of exposure to nickel and its compounds are inhalation of dusts and fumes containing nickel, and skin contact. Although nickel is present in food and water the intake is inefficient via mouth and through the gastrointestinal tract. An exception is when nickel is consumed in drinking-water on an empty stomach. This may be a particular risk to persons who already have been sensitized to nickel. Ingestion of large doses of nickel compounds causes intestinal disorders, convulsions and asphyxia.

Inhalation of dusts and fumes containing nickel causes irritation of the eyes, skin and respiratory tract. Repeated inhalation may result in loss of the sense of smell, in bronchial asthma, pulmonary fibrosis and pneumoconiosis. Inhalation of metallic nickel dust and dust contaminated by nickel compounds, for example nickel sulphide, is carcinogenic to humans. The risk of nasal and lung cancer is especially high.

Nickel deposited in the lungs may accumulate in the tissues. It is removed at a rate dependent on the solubility. The decontamination process is slow for metallic nickel and nickel oxide dusts.

Exposure to nickel carbonyl by accidental inhalation usually causes immediate mild, non-specific symptoms, such as nausea, headache and chest pain, which will disappear in a few hours. Delayed serious symptoms may appear 12 hours to 5 days after exposure. Death may occur 4 to 13 days after exposure; surviving patients may suffer from pulmonary insufficiency.

Repeated exposure to nickel carbonyl causes sleeplessness, headache, dizziness, weakness, poor memory, tightness in chest, loss of hair, loss of libido, and has been confirmed to involve risk of nasal and lung cancer.

Nickel dermatitis, `nickel itch', is the most common result of nickel exposure. It is primarily developed under hot and humid conditions when the skin is moist, such as when working with nickel compounds in nickel-plating, and mostly affects the hands and arms.

Nickel and its compounds are well-known skin sensitizers; nickel allergy is not limited to occupational exposure but may develop from exposure to nickel from various sources, such as coins, handles, jewelry, zippers and metal buttons in clothes, and medical prostheses containing nickel.

Nickel is a possible respiratory sensitizer and may have effects on the immune system.

Occupational hazards are mainly related to long-term exposure as acute nickel toxicity is of lesser importance, with the exception of exposure to nickel carbonyl.

3. Occupational use and exposure

Nickel ore is concentrated using mechanical methods: flotation and magnetic separation after crushing the mined minerals. Nickel concentrate is converted to nickel sulphide by `roasting' and then refined using electrolysis or the Mond process. In the Mond process, nickel is converted to nickel carbonyl with carbon monoxide at 50^oC. Nickel carbonyl decomposes at elevated temperatures (above 60^oC) and pure nickel powder is produced.

Nickel is widely used in alloys. Stainless steel contains 6-34% nickel. A typical stainless steel is an alloy of iron, 18% chromium and 8% nickel (by weight). Corrosion-resistant special alloys, such as Monel® containing 66% of nickel and 32% of copper, have applications in the dairy and food industry equipment.

Nickel alloys are also extensively used in the casting of machine parts, coinage, and in the production of electronic equipment and magnetic tapes.

Nickel gives a hard and resistant surface which is easy to polish and suitable for consumer products such as car components, household furniture and water taps. Nickel compounds are used in electroplating baths (nickel sulphate), in batteries (nickel hydroxide), marine anti-fouling paint, textile dyes and in ceramics and glass. Nickel catalysts take part in processes in oil refineries, coal production and plastic industry. Edible oil may be hardened using nickel compounds as catalyst in the process.

Hazardous exposure may take place when working with and in processes such as:

• mining, smelting and `roasting' (Mond process) of nickel ore
• production of nickel cathodes and batteries
• electrolytic purification of nickel metal
• production of stainless steel
• mechanical engineering industry using stainless steel and other nickel alloys
• surface treatment and finishing of metal parts (electroplating and metal spraying)
• manufacture of vehicles
• manufacture of tools, instruments and electronic equipment
• petroleum refineries
• glass, pottery and ceramic workshops
• welding, grinding, polishing and repairing appliances and objects made of stainless steel and other nickel alloys
• manufacture of disinfectants
• dyeing using colours containing nickel
• enameling
• paint and varnish production (colours containing nickel)
• jewellery work
• pen point and ink production
• production of machine parts (for example, spark plugs)

Nickel metal and nickel oxides, carbonates or sulphides in the form of powder, in quantity range of 1 000 kg, and nickel carbonyl in range of 10 kg, have been found to pose a potential risk of causing a major chemical accidents. They are included in the list of major hazard chemicals by the European Union and the ILO.

4. Safety measures and monitoring

At present there are only a few substitutes for nickel. Aluminum, coated steel, titanium and plastic have some industrial application replacing nickel; some processes may use platinum, cobalt or a copper catalyst to replace nickel.

Dusty working conditions, inadequate working methods and poor personal hygiene considerably increase the exposure to nickel. These problems can be solved by ventilation, planning the process and work methods to keep safety of the worker in mind, as well as by preventing exposure to nickel of nearby colleagues. In many countries a closed system or an effective local exhaust ventilation is required for fumes and mists containing nickel which arise, for example, from nickel electrolytic baths and surface spraying. Skin contact to nickel salt solutions can be prevented by using protective clothing, gloves, eye and face protection.

Pickling baths can be covered with floating plastic balls.

Nickel exposure in welding is often related to stainless steel and combined with exposure to fumes containing chromium. Choosing a less hazardous process, such as the use of MIG (Metal Inert Gas) welding instead of manual metal arc welding, reduces the exposure.

As exposure to nickel fumes and compounds include a risk of sensitization and may cause cancer, medical surveillance is obligatory in many countries. Medical records should also contain comprehensive medical and work histories with special attention to skin conditions, allergies, respiratory tract illnesses and smoking habits. Records should be kept long enough after the last exposure to nickel (30-40 years), as symptoms may appear after a long latency period.

Table 7. Threshold limit values related to airborne contaminants of nickel and its compounds (ACGIH)

5. Waste disposal

Nickel alloys may be recycled. The production of secondary nickel from scrap recovery is a major source of nickel. Recycled scrap is generally melted and refined, and then used to produce nickel alloys similar in composition to those in which it entered the recycling process.

Nickel compounds should be treated as hazardous waste. Nickel compounds from various industrial sources may also be regenerated and reused. If that is not practical, insoluble nickel compounds may be landfilled into dumps authorized for chemical waste. Soluble nickel waste should be collected in an organized manner, and be treated chemically to form insoluble compounds which then, after filtering and drying, may be buried in an approved landfill.

Nickel can be recovered and recycled from various industrial processes.

Nickel carbonyl is a toxic, volatile and flammable liquid; the vapour may spontaneously ignite at room temperature. Such industrial waste should be handled with great respect avoiding all contact with living organism or with the environment. Incineration should only be carried out in a plant designed for chemical waste.

6. Nickel in the environment

Nickel is distributed into the environment from natural sources and industrial activities. It is found in all parts of the biosphere. Major releases of man-made nickel come from burning of fossil fuel, especially coal. Locally important emissions are released from mills enriching nickel ore. Uncontrolled emissions and disposal of waste may have adverse effects on the environment.

Nickel is introduced into water systems from atmosphere aerosols where it is mainly present as solid particles (dust). Industrial and municipal waste and natural erosion of soil and rocks add various amounts of nickel compounds into waterways. Acid rain may leach nickel and other metals from plants and soil.

Depending on the type of soil, nickel moves with different speed through the soil, finally reaching groundwater.

Nickel is an essential trace element for some animals, plants and bacterial enzymes. High concentrations and lasting exposure cause irritation, various adverse effects and tumors.

Nickel allergy is very common among human beings but animal experiments show allergic reactions only under specific conditions.

Plants accumulate nickel. High levels cause retarded growth in some species.

There is no evidence for biomagnification of nickel in the food chain, and nickel has only a very slight accumulation capacity in fish and wildlife.

Although nickel is not considered to be a broad scale global contaminant, devastating effects and ecological changes can be observed near nickel emitting sources. Natural concentrations of available nickel vary up to 20 ppm of soil (dried in air). When the nickel concentration is 50-200 ppm the soil is contaminated, and more than 200 ppm in dry soil may be considered heavy contamination.

ANNEX 1.

CLASSIFICATION OF CHROMIUM COMPOUNDS IN EUROPEAN UNION

conc. concentration

* S-phrases in parenthesis should be added to products sold for general public. For example, concentrated acetic acid should be, when in storage, locked up and kept out of the reach of children.

ANNEX 2.

CLASSIFICATION OF NICKEL COMPOUNDS IN EUROPEAN UNION COUNTRIES

* S-phrase S2 in parenthesis should be added to products sold for general public.

Continue to Part VIII: Corrosive Materials