F. William Sunderman, Jr.
Nickel (Ni) compounds of interest include nickel oxide (NiO), nickel hydroxide (Ni(OH)2), nickel subsulphide (Ni3S2), nickel sulphate (NiSO4) and nickel chloride (NiCl2). Nickel carbonyl (Ni(CO)4) is considered in a separate article on metal carbonyls.
Occurrence and Uses
Nickel (Ni) comprises 5 to 50% of the weight of meteorites and is found in ores in combination with sulphur, oxygen, antimony, arsenic and/or silica. Ore deposits of commercial importance are principally oxides (e.g., laterite ores containing mixed nickel/iron oxides) and sulphides. Pentlandite ((NiFe)9S8), the major sulphide mineral, is commonly deposited in association with pyrrhotite (Fe7S6), chalcopyrite (CuFeS2) and small amounts of cobalt, selenium, tellurium, silver, gold and platinum. Substantial deposits of nickel ores are found in Canada, Russia, Australia, New Caledonia, Indonesia and Cuba.
Since nickel, copper and iron occur as distinct minerals in the sulphide ores, mechanical methods of concentration, such as flotation and magnetic separation, are applied after the ore has been crushed and ground. The nickel concentrate is converted to nickel sulphide matte by roasting or sintering. The matte is refined by electrowinning or by the Mond process. In the Mond process, the matte is ground, calcined and treated with carbon monoxide at 50 °C to form gaseous nickel carbonyl (Ni(CO)4), which is then decomposed at 200 to 250 °C to deposit pure nickel powder. Worldwide production of nickel is approximately 70 million kg/year.
More than 3,000 nickel alloys and compounds are commercially produced. Stainless steel and other Ni-Cr-Fe alloys are widely used for corrosion-resistant equipment, architectural applications and cooking utensils. Monel metal and other Ni-Cu alloys are used in coinage, food-processing machinery and dairy equipment. Ni-Al alloys are used for magnets and catalyst production (e.g., Raney nickel). Ni-Cr alloys are used for heating elements, gas turbines and jet engines. Alloys of nickel with precious metals are used in jewellery. Nickel metal, its compounds and alloys have many other uses, including electroplating, magnetic tapes and computer components, arc-welding rods, surgical and dental prostheses, nickel-cadmium batteries, paint pigments (e.g., yellow nickel titanate), moulds for ceramic and glass containers, and catalysts for hydrogenation reactions, organic syntheses and the final methanation step of coal gasification. Occupational exposures to nickel also occur in recycling operations, since nickel-bearing materials, especially from the steel industry, are commonly melted, refined and used to prepare alloys similar in composition to those that entered the recycling process.
Human health hazards from occupational exposures to nickel compounds generally fall into three major categories:
- rhinitis, sinusitis and respiratory diseases
- cancers of the nasal cavities, lungs and other organs.
The health hazards from nickel carbonyl are considered separately, in the article on metal carbonyls.
Allergy. Nickel and nickel compounds are among the most common causes of allergic contact dermatitis. This problem is not limited to persons with occupational exposure to nickel compounds; dermal sensitization occurs in the general population from exposures to nickel-containing coins, jewellery, watch cases and clothing fasteners. In nickel-exposed persons, nickel dermatitis usually begins as a papular erythema of the hands. The skin gradually becomes eczematous, and, in the chronic stage, lichenification frequently develops. Nickel sensitization sometimes causes conjunctivitis, eosinophilic pneumonitis, and local or systemic reactions to nickel-containing implants (e.g., intraosseous pins, dental inlays, cardiac valve prostheses and pacemaker wires). Ingestion of nickel-contaminated tap water or nickel-rich foods can exacerbate hand eczema in nickel-sensitive persons.
Rhinitis, sinusitis and respiratory diseases. Workers in nickel refineries and nickel electroplating shops, who are heavily exposed to inhalation of nickel dusts or aerosols of soluble nickel compounds, may develop chronic diseases of the upper respiratory tract, including hypertrophic rhinitis, nasal sinusitis, anosmia, nasal polyposis and perforation of the nasal septum. Chronic diseases of the lower respiratory tract (e.g., bronchitis, pulmonary fibrosis) have also been reported, but such conditions are infrequent. Rendall et al. (1994) reported the fatal acute exposure of a worker to inhalation of particulate nickel from a metal arc process; the authors stressed the importance of wearing protective equipment while using metal arc processes with nickel wire electrodes.
Cancer. Epidemiological studies of nickel-refinery workers in Canada, Wales, Germany, Norway and Russia have documented increased mortality rates from cancers of the lung and nasal cavities. Certain groups of nickel-refinery workers have also been reported to have increased incidences of other malignant tumours, including carcinomas of the larynx, kidney, prostate or stomach, and sarcomas of soft tissues, but the statistical significance of these observations is questionable. The increased risks of cancers of the lungs and nasal cavities have occurred primarily among workers in refinery operations that entail high nickel exposures, including roasting, smelting and electrolysis. Although these cancer risks have generally been associated with exposures to insoluble nickel compounds, such as nickel subsulphide and nickel oxide, exposures to soluble nickel compounds have been implicated in electrolysis workers.
Epidemiological studies of cancer risks among workers in nickel-using industries have generally been negative, but recent evidence suggests slightly increased lung cancer risks among welders, grinders, electroplaters and battery makers. Such workers are often exposed to dusts and fumes that contain mixtures of carcinogenic metals (e.g., nickel and chromium, or nickel and cadmium). Based on an evaluation of epidemiological studies, the International Agency for Research on Cancer (IARC) concluded in 1990: “There is sufficient evidence in humans for the carcinogenicity of nickel sulphate and of the combinations of nickel sulphides and oxides encountered in the nickel refining industry. There is inadequate evidence in humans for the carcinogenicity of nickel and nickel alloys.” Nickel compounds have been classified as carcinogenic to humans (Group 1), and metallic nickel as possibly carcinogenic to humans (Group 2B).
Renal effects. Workers with high exposures to soluble nickel compounds may develop renal tubular dysfunction, evidenced by increased renal excretion of β2-microglobulin (β2M) and N-acetyl-glucosaminidase (NAG).
Safety and Health Measures
A general protocol for health surveillance of workers exposed to nickel was proposed in 1994 by the Nickel Producers Evironmental Research Association (NiPERA) and the Nickel Development Institute (NiDI). The key elements are as follows:
Pre-placement assessment. The goals of this examination are to identify pre-existing medical conditions that may influence hiring and job placement, and to provide baseline data for subsequent functional, physiological or pathological changes. The assessment includes (i) detailed medical and occupational history, focusing on lung problems, exposures to lung toxins, past or present allergies (particularly to nickel), asthma and personal habits (e.g., smoking, alcohol consumption), (ii) complete physical examination, with attention to respiratory and skin problems and (iii) determination of the respiratory protective equipment that may be worn.
Chest x ray, pulmonary function tests, audiometric tests and vision tests may be included. Skin patch testing for nickel sensitivity is not routinely performed, because such tests could possibly sensitize the subject. If the organization conducts a biological monitoring programme for nickel-exposed workers (see below), baseline nickel concentrations in urine or serum are obtained during the pre-placement assessment.
Periodic assessment. The goals of periodic medical examinations, typically performed annually, are to monitor the worker’s general health and to address nickel-associated concerns. The examination includes the history of recent illnesses, symptom review, physical examination and re-evaluation of the worker’s ability to use the respiratory protective equipment required for particular tasks. Pulmonary symptoms are assessed by a standard questionnaire for chronic bronchitis. Chest x ray may be legally required in some countries; pulmonary function tests (e.g., forced vital capacity (FVC) and forced expiratory volume in 1 second (FEV1) are generally left to the physician’s discretion. Periodic cancer detection procedures (e.g., rhinoscopy, nasal sinus x rays, nasal mucosal biopsy, exfoliative cytological studies) may be indicated in workers with high-risk exposures in nickel refining.
Biological monitoring. Analyses of nickel concentrations in urine and serum samples may reflect the recent exposures of workers to metallic nickel and soluble nickel compounds, but these assays do not furnish reliable measures of the total body nickel burden. The uses and limitations of biological monitoring of nickel-exposed workers have been summarized by Sunderman et al. (1986). A technical report on analysis of nickel in body fluids was issued in 1994 by the Commission on Toxicology of the International Union of Pure and Applied Chemistry (IUPAC). The National Maximum Workplace Concentration Committee (NMWCC) of the Netherlands proposed that urine nickel concentration 40 µg/g creatinine, or serum nickel concentration 5 µg/l (both measured in samples obtained at the end of a working week or a work shift) be considered warning limits for further investigation of workers exposed to nickel metal or soluble nickel compounds. If a biological monitoring programme is implemented, it should augment an environmental monitoring programme, so that biological data are not used as a surrogate for exposure estimates. A standard method for the analysis of nickel in workplace air was developed in 1995 by the UK Health and Safety Executive.
Treatment. When a group of workers accidently drank water heavily contaminated with nickel chloride and nickel sulphate, conservative treatment with intravenous fluids to induce diuresis was effective (Sunderman et al. 1988). The best therapy for nickel dermatitis is avoidance of exposure, with special attention to work hygienic practices. Therapy of acute nickel carbonyl poisoning is discussed in the article on metal carbonyls.