Many metals, including nickel, are coming under increasing scrutiny by regulators because of real or alleged effects on the environment and human health. Nickel initially attracted attention because of a greater incidence of lung and nasal cancers among nickel smelter and refinery workers in the early decades of this century. Nickel-containing materials identified with these cancers are nickel oxides and subsulfides and to a lesser extent nickel sulfate. There is no compelling evidence that nickel metal itself causes cancer.
Workers are exposed by inhaling airborne particles, which can remain in the lungs for many years. The dusty conditions that existed in early nickel production operations have been eliminated. Today worker exposure is usually within regulated limits.
In the 1980's, under the leadership of the world-renowned Sir Richard Doll of Oxford University, an international team of epidemiologists conducted a major epidemiological study of early production operations. The data were ambiguous. The most confounding factor was that most of the workers smoked. The so-called "Doll" study concluded there was no evidence to suggest a health problem from insoluble nickel compounds (oxides and sulfides) at nickel concentrations less than 10 mg/cu meter. It also concluded there was no health problem from soluble nickel compounds (sulfate and chloride) at concentrations less than one mg/cu meter.
Most regulated limits today are one tenth of those exposures or less. While some operations occasionally exceed the limits, most are in compliance. Also, there is little evidence today of elevated incidence of lung or nasal cancers among nickel producers or users relative to local populations.
Nickel Dermatitis. The other significant health effect of nickel is dermatitis. This is a phenomenon associated with soluble nickel compounds or nickel metal dissolved in sweat that penetrates skin causing an allergic reaction in genetically predisposed individuals. As a workplace exposure, this is probably a greater risk than is lung cancer by inhalation of aerosols of nickel sulfate, chloride or sulfamate.
As many as 10-20 pct of women and one to two pct of men are nickel sensitive. It is caused primarily by wearing inexpensive, nickel-plated jewelry. Nickel plating is common in jewelry making, but often the nickel is plated with silver, gold, platinum or other noble metals. Inexpensive jewelry simply stops at the nickel plate, and, thus, nickel metal is in direct contact with the skin. If the contact is long enough for sweat to react with the nickel, the dissolved nickel can cause an allergic reaction.
It is important to recognize that it is not nickel metal that is the problem, but rather dissolved nickel. Nickel that is not in contact with the skin long enough to react with sweat is not a problem; nor is nickel in a form that does not react with sweat, such as most stainless steels. While there are problems with inexpensive nickel-plated jewelry, there are seldom problems with stainless steel wrist watches.
Concerns in the Plating Industry. Nickel-platers can get dermatitis from skin contact with soluble nickel compounds. They can experience respiratory problems from inhaling airborne aerosols or other nickel-containing particles. The preventive measures are gloves and ventilation and/or masks.
Gloves are a better preventive than cure for dermatitis. Once sensitized to nickel, gloves may not eliminate the problem because they enhance the generation of sweat, which encourages dermatitic reactions. Some nickel-sensitized workers have ultimately had to change their work functions to eliminate exposure to soluble nickel. As for respiratory effects, ventilation is preferable to a mask, but the latter is an additional safety feature that minimizes exposure.
Exposure Measurement and Data. Nickel exposures in most nickel plating operations are unknown. Most platers feel they simply do not have the resources to measure exposure. Those who do generally buy the service rather than do it themselves.
Details of exposure measurement are extensive and can be found in the "Safe Use of Nickel in the Workplace." This is a health guide published in June 1994, as a joint effort of the Nickel Producers Environmental Research Association (NiPERA) and the Nickel Development Institute (NiDi). The guide is a comprehensive reference to the health effects of nickel and its safe use in the workplace. Included in the guide is a description of devices and procedures for measuring exposure to various nickel-containing substances.
The data from various nickel plating operations show that while exposures exceed regulated limits in parts of some operations, they are generally lower and in compliance with regulated limits overall.
Nickel Exposure Limits. Permissible exposure limits (PELs) are different but similar from one country to another. In the United Kingdom the PEL for nickel metal and all nickel compounds is 0.5 mg/cu meter. There is no distinction made of nickel in various forms. In the U.S. the limits are one mg/cu meter for nickel metal and insoluble nickel compounds and 0.1 mg/cu meter for soluble compounds. U.S. courts required OSHA to rescind the 0.1 mg/cu meter limit because it had been improperly established. Thus the only legally binding PEL for nickel and any of its compounds, except for nickel carbonyl, is one mg/cu meter.
The American Conference of Governmental Industrial Hygienists (ACGIH) has proposed lower Threshold Limit Values (TLV's) that could be adopted by OSHA in 1997 or thereafter. The initial proposal in 1989 stated that the TLV for nickel and all its compounds should be decreased to 0.05 mg/cu meter. This TLV has been consistently opposed by NiPERA and NiDi. As a result, ACGIH has delayed decision on the matter annually since the original proposal.
ACGIH is now thinking of revising its proposed TLV's to 0.5 mg/cu meter for nickel metal, 0.1 mg/cu meter for insoluble nickel compounds and 0.05 mg/cu meter for soluble nickel compounds. While these limits are still unacceptable to industry, they are an improvement over a proposed TLV of 0.05 mg/cu meter for all nickel substances. ACGIH is also likely to propose that nickel and all its compounds be classified as confirmed human carcinogens. Presently this designation applies only to nickel oxides, subsulfides and nickel carbonyl. NiDi and NiPERA feel that, based on the evidence, inclusion of other nickel substances in this category is unjustified.
Risk Assessment. The attitude of this proposal is that if a substance is shown to be hazardous, causing problems under certain imposed conditions, then it should be regulated as though it would cause the same problem under any less severe conditions.
The industrial, and much of the scientific, community promotes an alternative view that regulation should be risk based. This means that under given conditions an undesirable effect actually does happen, not whether it might happen.
As an example: gasoline is a hazardous substance, but its use in automobiles is not a significant risk because it is kept in closed gas tanks. Exposure limits should be set at levels above which it is known there are unacceptable risks, not at lower limits simply because the substance is regarded as hazardous.
The most important information for regulating substances is actual exposure and worker health records. If the health records indicate no elevated health effects relative to the surrounding community, then there would seem no reason to regulate exposures below those that have prevailed in practice. This is the position NiDi adopts with regulatory agencies.
Wastewaters. In addition to workplace exposures, nickel-platers must also be concerned about emissions of nickel-containing gases to the air; liquids to sewers or drains; and solids to recyclers or landfill.
Regulations govern the disposal of aqueous or other effluents to sewers or natural water courses, including nickel. Again, limits vary with jurisdictions and may be more constrained in regions or municipalities than nationally. It is the responsibility of each plater to determine the regulations affecting him. Nickel limits for aqueous effluents presently established by the U.S. EPA are 1.1 mg/liter a day and 0.5 mg/liter a month average. Most plating operations cannot comply directly with effluent wastewater regulations wherever they are. Wastewaters are therefore commonly treated with lime to neutralize and precipitate residual nickel concentrations so that effluents are in compliance.
Solid Wastes. Most of the solid wastes generated by platers are precipitates from aqueous effluents. Characteristically, these are relatively small quantities by weight and volume and are accumulated in drums to be picked up at appropriate intervals by recyclers, disposal agencies or both. They assume responsibility for the environmental fate of the waste either by recycling or disposal. Waste for disposal must either meet leachate tests before going to landfill or discarded at higher cost in hazardous waste landfills.