SAFE USE OF NICKEL IN THE WORKPLACE Last Revised: 5/1997
7. WORKPLACE SURVEILLANCE
Knowledge of general exposure conditions within the workplace is another element of a worker protection program. Workplace surveillance entails understanding the applicable legislative occupational exposure limits and implementing an air monitoring program that allows for comparison of worker exposures to these limits. Both of these components are discussed in detail in this section.
7.1 AIR MONITORING
Where workers are known to be exposed to nickel in the air, it is necessary to conduct air monitoring in order to determine whether worker exposures fall within permissible limits. A successful air monitoring program begins with a good understanding of the physical layout and processes of the workplace. Before any monitoring is undertaken, a visual survey of the site should be conducted in order to identify potential areas of significant exposure. Material Safety Data Sheets (MSDS) should also be reviewed and discussed with employees as another means of identifying potential problem areas. Only when these initial surveys have been completed and analyzed should the employer embark on an air monitoring program.
Characterization of exposure is a complex task that is best done by trained personnel. For facilities that lack the appropriate staff, certified occupational hygiene consultants are the suggested alternative. Governmental organizations may provide assistance on air monitoring or advice on where to obtain skilled help.
The components of an air monitoring program are:
- development of a sampling strategy,
- purchase or rental of sampling equipment and supplies,
- calibration of equipment,
- sample collection,
- sample analysis,
- calculation of exposure concentrations,
- determination of compliance status,
- notification of employees of the results, and
- documentation and recordkeeping.
Specific requirements for each of these components may differ from country to country; therefore, employers should consult the appropriate government agency or code for detailed procedures.
Air monitoring is not an end in itself but should be considered part of an overall program of risk assessment and management. Upon completion of an air monitoring survey, it is necessary to evaluate the results and decide whether any action is required to modify the sampling procedures or working environment.
Current nickel standards generally differentiate only between water-soluble and insoluble compounds and nickel carbonyl. Thus, the application of air monitoring techniques that collect total dust samples in combination with analyses that distinguish between compound solubilities has been sufficient to determine compliance. Recent work, however, indicates that health effects associated with nickel exposures may be dependent upon a number of factors, including chemical form (speciation), particle size, and solubility within biological fluids (as opposed to water) (see Section 5). Therefore, it is recommended that each worksite be characterized with regard to the individual nickel species present in the air and to the distribution of particle sizes in the aerosols.
New sampling instruments have been developed that measure inhalable aerosol (Mark and Vincent, 1986). The performance of these devices closely matches the human inhalation curves adopted by the International Standards Organisation (ISO, 1984), the Comité Européen Normalisation (CEN, 1993) and the American Conference of Governmental Industrial Hygienists (ACGIH, 1993-94). These organizations are moving in the direction of replacing the traditional 'total' aerosol concept with a new sampling convention based on human inhalability. It should be noted that side-by-side comparisons of the inhalable sampler to "total" aerosol samplers (such as the 37 mm sampler) have shown the inhalable sampler to consistently measured 2-3 times more nickel aerosol than the 'total' sampler. (Tsai et al., 1995; Tsai et al., 1996a and 1996b).
The components of an air sampling program are briefly discussed below.
7.1.1 Sampling Strategy
The sampling strategy selected depends on the goal of the sampling program, whether it is to ascertain compliance, to provide data for research, or to investigate a particular workplace problem. The strategy may seek to evaluate exposures of all workers or a representative worker. Sampling may be conducted to develop an exposure profile (e.g. full shift sampling over several consecutive days), to examine the same job on different shifts, or to characterize the exposure associated with a specific task. Some strategies evaluate concentrations at the source and extrapolate these results in order to estimate worker exposure. Alternatively, sampling might be conducted to determine the source of exposure where potential "problem areas" have been identified through biological monitoring but the source of exposure has not been identified.
The development of a sampling protocol which allows hygienists to evaluate exposure to Ni-containing aerosols relative to occupational exposure limits has recently been completed (Rappaport et al., 1995; Lyles and Kupper, 1996). This protocol explicitly recognizes both within- and between-worker sources of exposure variability. Thus, overexposure is defined as the probability that a randomly selected worker would have a mean exposure above the exposure limit, for a particular time-period. In addition, this protocol provides guidelines that would allow the collection of solid and reliable data for future epidemiological studies.1
1More information on this research is available from NiPERA
Since operating conditions and individual methods of work can vary enormously, exposure monitoring of the workplace tends to be an inexact science. It is therefore important that the sampling strategy be flexibly designed to account for differences in worker and job variability and to obtain statistically valid results. This may mean that different sampling strategies should be employed in different areas of a plant. Other sources of information on sampling strategies include the aforementioned HSE in the U. K. and OSHA in the U. S., as well as the U. S. National Institute for Occupational Safety and Health (NIOSH).
7.1.2 Monitoring Frequency
Considerations in determining monitoring frequency should include: regulatory requirements, changes in the process, work practices or other factors that affect exposure, and evidence of health effects. Periodic monitoring can be used to evaluate the effectiveness of exposure controls and control equipment maintenance programs.
7.1.3 Equipment
Simply described, an air sampling device consists of an electrically-operated air sampling pump, sampling medium, and tubing to connect the medium to the pump. This equipment may be portable and worn on a worker, generally for an eight-hour (one shift) period, or it may be static with long lasting batteries or connection to a main supply of electricity. The sampling media may be a filter, solvent, or solid absorbent. Possible contact sources for names and addresses of manufacturers and suppliers of environmental monitoring equipment are listed in Appendix A. Filter media and filter holders may be purchased through suppliers and assembled in-house or can be bought pre-assembled. Personal and/or static sampling devices may be used depending upon the requirements of the sampling program, but it is important to note that static sampling frequently underestimates exposures.
A second type of device available for estimating the concentration of soluble aerosols of nickel is the detector tube and manual pump. Soluble airborne contaminants produce a color change as the pump draws the air through the detector tube. The length of the stain is proportional to the concentration. Since the typical accuracy of these readings is ± 25 percent and the lower limit of detection is 0.25 mg Ni/m3, this device should serve only as a screening tool to aid in deciding whether to conduct full shift monitoring. It should also be noted that FeSO4 interferes by producing a similar color change. A detector tube is also available for nickel carbonyl. However, as its detection limit is only 0.1 ppm, its use is limited. (See Appendix A for possible contact sources that may be able to suggest names of suppliers.)
Selecting the appropriate equipment depends on the goal behind sampling and any specifications established by the regulating authority. Pumps are generally interchangeable since they all have similar functions, but dust collection methods vary depending on whether particle size selective sampling of the dust is desired. Furthermore, some filtering media can be used to distinguish between different forms of nickel more readily than others. Therefore, the objectives of the sampling program and guidelines or regulations that apply should be determined before selecting the sampling equipment (see Section 7.2). Manufacturers, suppliers, industry trade associations, or associations that support occupational health professionals may be sources of sampling information. Appendix A lists some possible contacts for these sources. Another alternative is to use published methods such as those prepared by NIOSH (1994a, b, c) some of which are which are reproduced in Appendix B. In addition to the air sampling device, calibration and quality control are fundamental to valid monitoring results. Equipment to calibrate the volumetric flowrate of the air sampling device is essential. Soap bubble meters, rotameters, or automated instruments may be used for such purposes and are available through equipment manufacturers and suppliers.
7.1.4 Sampling Technique For personal sampling, the position of the sampling medium should allow the device to collect air from the employee's breathing zone. This is defined by OSHA in the U. S. as a two-foot diameter sphere centered in the middle of the head. For welders, the filter medium should be placed inside the welding helmet because the helmet provides some protection and inaccurate results would be obtained otherwise. The pump, which is frequently worn on a belt, and the tubing should not impede the worker's activities or pose a safety hazard. In all cases, the employees' support should be sought by explaining the reason for sampling and asking for their participation. Employees should also be instructed to notify the supervisor or person conducting the sampling if the equipment malfunctions or if they need to have it removed. During the shift, periodic checking of the battery charge and pump flowrate should be performed and documented to ensure sample validity and accurate volume calculation. This is especially important in very dusty operations where high filter loadings may occur and cause the pump flowrate to decrease. Some pumps are designed to compensate for this by automatically increasing the pump speed and, thus, the flowrate; however, periodic checks are still recommended. The person sampling should also note the temperature and barometric pressure so that adjustments to the volume of air collected can be made. Through work observation, a job description should be developed that includes information about work practices and other factors that potentially influence exposures. This can be used to explain sample results and to aid in decisions on exposure control should the need arise. This information may include production rates, time spent on breaks, the use of ventilation, work practices, and proximity to the source of exposure. An example of an OSHA data collection sheet is provided in Appendix C. In addition to recording descriptive information and documenting pump checks, the collection sheet can serve as a log for ambient conditions relevant to sample collection, pump and filter media identification numbers (including sample blanks), and sample duration. Any use of respiratory protection also should be documented.
7.1.5 Sample Analysis Several methods exist for analyzing samples. The most common method is to treat the sampling filter with an appropriate acid solution, thereby releasing the entrained nickel for subsequent analysis by atomic absorption. The definitive method has been described by the International Union of Pure and Applied Chemistry (IUPAC) (Brown et al., 1981). X-ray spectrometry of the filter is a simple and accurate alternative if the equipment is available. In samples with relatively high concentrations of nickel (µg/g or µg/dl range) Inductively Coupled Plasma - Atomic Emission Spectrometry (ICP-AES) allows multielement detection including the reliable analysis of nickel ions (see Appendix B). Speciation currently is used only as a research procedure since it is time consuming and expensive. As the importance of speciation has already become more widely recognized by researchers and regulators alike, it may become more commonplace, or even mandatory, to analyze samples for specific species. Alternatively, it may be considered adequate to first characterize the workplace atmosphere by a detailed species analysis (Zatka et al., 1992) and then use conventional methods to measure total nickel and apportion the results to specific species. In selecting a method, an important consideration is the requirements of the applicable regulations. These regulations may require that the laboratory conducting the analysis participate in a qualification or certification program to ensure accurate results. If no regulations exist, then the objectives in sampling should help determine the choice of analytical methods. Evidence of effective quality control will be essential. Contacts and resources for additional guidance are listed in Appendix A. Whenever possible, the selected sampling procedure should be discussed with the laboratory that will perform the analysis prior to sampling. Frequently, the laboratory can also provide valuable guidance on potential interferences, the number of samples and field blanks needed, sample storage, and transportation.
7.1.6 Calculating Exposure Results An employee's time-weighted average exposure concentration ("TWAEC") is calculated by taking the sum of the products of the analytically-determined concentration for each sampling period, including overtime (see Appendix D), and the duration of the corresponding sampling period and dividing this sum by the total sampling time as shown in the equation below:
C1 T1 + C2 T2 + ... + Cn Tn
 |
| T1 + T2 + ... + Tn | where:
Cn = concentration for sample n in mg/m3,
and
Tn =sampling time for sample n in minutes. Because sampling time rarely equals eight hours exactly, a decision regarding exposures during any unsampled periods must be made before comparing the result to eight-hour TWA standards (see Appendix D).
7.1.7 Determining Compliance Since procedures for determining compliance may vary from country to country, the employer should understand the appropriate regulatory requirements for the specific locale in which they are operating. A number of statistical techniques are published that allow determination of compliance with an associated degree of confidence. In most cases, data collected from portable personal sampling equipment will be preferred over that collected from static samplers.
7.1.8 Employee Notification Good industrial hygiene practices encourage the employer to provide the sampled individuals who have cooperated in the air monitoring program (and those unsampled employees whose exposures they are deemed to represent) with their personal sampling results and an explanation of their meaning. Group results should also be shared with the workforce. Where the results of sampling a "representative" individual(s) are made available to other workers, consideration should be given to withholding personal identifiers. Some authorities may require this notification and specify a date by which this should be done relative to the date of receipt of the results.
7.1.9 Recordkeeping Some countries may require that exposure records be maintained by the employer for a number of years. For example, in the U. S., this recordkeeping is required for at least 30 years from the date on which the exposure measurement is taken. In the EU, the requirement is for at least 40 years following exposure. Regulations generally require that employees (and possibly their representatives as well) be granted access to these records. Any exposure monitoring data gathered and recorded should be subject to rigorous quality control. The International Organization for Standards (ISO) has developed a set of useful guidelines for implementing a quality assurance program (see Appendix A for a possible contact).
7.2 CARCINOGENIC CLASSIFICATIONS In recent years, a number of organizations and international agencies have evaluated the evidence regarding the carcinogenic effects of nickel, all with the intent of delineating the potential differences in the bioavailability and toxicity of various nickel species. Based largely on the 1990 findings of the ICNCM, IARC concluded that there is sufficient evidence in humans for the carcinogenicity of nickel sulfate and the combinations of nickel sulfides and oxides encountered in the nickel refining industry. Conversely, it concluded that there is inadequate evidence in humans for the carcinogenicity of metallic nickel and nickel alloys. Based upon its evaluation of both human and experimental data, IARC has classified nickel compounds as Group 1 (carcinogenic to humans) and metallic nickel as Group 2B (possibly carcinogenic to humans) (IARC, 1990). In 1991, the Commission of the European Communities concluded that certain specific nickel sulfides (Ni3S2 and NiS) and oxides (NiO, Ni2O3 and NiO2), as well as "work involving exposure to dust, fumes and sprays produced during the roasting and electrorefining of cupro-nickel mattes," should be classified as Category 1 carcinogens. Category 1 carcinogens are "Substances [or processes] known to be carcinogenic to man. There is sufficient evidence to establish a causal association between human exposure to the substance [process] and the development of cancer" [15th Adaptation to Technical Progress (91/632/EEC) of the Packaging and Labeling Directive (67/548/EEC). The above nickel compounds have been assigned the risk phrase, "May cause cancer by inhalation." Nickel metal and certain other compounds (sulfate, carbonate, hydroxide and carbonyl) were classified as Category 3 carcinogens, "Substances which cause concern for man owing to possible carcinogenic effects but in respect of which the available information is not adequate for making a satisfactory assessment." In a 1986 evaluation, the U. S. Environmental Protection Agency (U. S. EPA) classified nickel subsulfide and nickel refinery dust from pyrometallurgical sulfide nickel matte refineries as Group A carcinogens, indicating that there is sufficient overall evidence that these forms of nickel are carcinogenic to humans (U. S. EPA, 1986). The Agency also classified nickel carbonyl as a Group B2 probable carcinogen. However, this classification was based upon a rodent study showing somewhat questionable statistical results. The American Conference of Governmental Industrial Hygienists (ACGIH) (a non-legislative organization) published a list of proposed changes to carcinogen classifications and TLVs for nickel compounds in January, 1997 (see Section 7.1.5). The newly proposed carcinogen classifications for nickel compounds are:
- A5 (Not suspected as a human carcinogen) for metallic nickel,
- A4 (Not classifiable as a human carcinogen) for soluble nickel,
- A1 (Confirmed human carcinogen) for insoluble nickel,
- A1 for nickel subsulfide, and
- no classification for nickel carbonyl.
For more information on the carcinogenicity of nickel, its compounds and alloys, the reader is referred to the ICNCM Report (ICNCM, 1990). In addition, the recent publications of the Commission of the European Communities (Berlin et al., 1990), the U. K. Health and Safety Executive Advisory Committee on Toxic Substances (Fairhurst and Illing, 1987), the International Programme on Chemical Safety (IPCS, 1991) and IARC (1990) evaluate the pertinent human and animal carcinogenicity studies. Maximilien (1989) also provides a detailed review of the animal carcinogenesis studies on nickel and its compounds.
7.3 REFERENCES
ACGIH. American Conference of Governmental Industrial Hygienists. (1993-94). Threshold limit values for chemical substances and physical agents and biological exposure indices. Cincinnati, OH: ACGIH.
Berlin, A., Draper, Krug, E., Roi, R., Van der Venne, M. Th., eds. (1990). The Toxicology of Chemicals: v. 2, Carcinogenicity - Summary Reviews of the Scientific Evidence. Brussels, Belgium: Commission of the European Communities (CEC). 145 p.
Brown, S. S., Nomoto, S., Stoeppler, M., Sunderman, F. W., Jr. (1981). IUPAC reference method for analysis of nickel in serum and urine by electrothermal atomic absorption spectrophotometry. Clin. Biochem. 14: 295-299.
CEN - Comité Européen de Normalisation. (1994). General requirements for the performance of procedures for workplace measurements. Draft standard prEN482. Brussels, Belgium: Commission of European Communities.
Fairhurst, S. and Illing, H. P. A. (1987). The toxicity of nickel and its inorganic compounds. U. K. Health and Safety Executive Advisory Committee on Toxic Substances. H. M. S. O.
IARC. International Agency for Research on Cancer. (1990). IARC monographs on the evaluation of carcinogenic risks to humans of chromium, nickel, and welding: v. 49. Geneva, Switzerland: World Health Organization. pp. 257-446.
ICNCM. International Committee on Nickel Carcinogenesis in Man. (1990). Report of the International Committee on nickel carcinogenesis in man. Scand. J. Work Environ. Health 16(1): 1-84.
ISO. International Standards Organisation. (1992). Air quality - particle size fraction definitions for health related sampling. Technical report no. ISO/TR/7708-1983. Geneva, Switzerland: International Standards Organisation.
IPCS. International Programme on Chemical Safety. (1991). Environmental Health Criteria 108: Nickel. Geneva, Switzerland: World Health Organization. 383 p.
Lyles, R.H. and Kupper, L. L. (1996). On strategies for comparing occupational exposure data to limits. American Industrial Hygiene Association Journal, 57: 6-15.
Mark, D., Vincent, J. H. (1986). A new personal sampler for airborne total dust in workplaces. Ann. Occup. Hyg., 30, 89-102.
Maximilien, R. (1989). Critical review of animal carcinogenesis by nickel and its inorganic compounds: Parts 1 and 2. Fontenay aux Roses, France: Euratom-CEA. 366 p.
NIOSH. National Institute of Occupational Safety and Health. (1994a). Method No. 7300: Elements. NIOSH Manual of Analytical Methods. 4th ed. Issue 2, 15 August 1994.
NIOSH. National Institute of Occupational Safety and Health. (1994b). Method No. 8005: Elements in Blood or Tissue. NIOSH Manual of Analytical Methods. 4th ed. Issue 2, 15 August 1994.
NIOSH. National Institute of Occupational Safety and Health. (1994c). Method No. 8310: Metals in Urine. NIOSH Manual of Analytical Methods. 4th ed. Issue 2, 15 August 1994.
Rappaport, S. M., Lyles, R. H., Kupper, L. L. (1995). An exposure- assessments strategy accounting for within- and between-worker sources of variability. Ann. Occup. Hyg., 39, 469-495.
Tsai, P. J., Vincent, J. H., Wahl, G., Maldonado, G. (1995). Occupational exposure to inhalable aerosol in the primary nickel production industry. Occup. Environ. Med., 52, 793-799.
Tsai, P. J., Vincent, J. H., Mark, D. (1996a). Semi-empirical model for the aspiration efficiencies of personal aerosol samplers of the type widely used in occupational hygiene. Annals of Occupational Hygiene 40: 113-133.
Tsai, P. J., Werner, M. A., Vincent J. H., Maldonado, G. (1996b). Exposure to nickel-containing aerosols in two electroplating shops: comparison between inhalable and 'total' aerosol. Applied Occupational and Environmental Hygiene 11: 484-492.
U.S. EPA. U.S. Environmental Protection Agency. (1986). Health Assessment Document for Nickel and Nickel Compounds. EPA/600/8-8 3/012FF. Washington, DC: U. S. Environmental Protection Agency. 466 p.
Zatka, J. V., Warner, J. S., Maskery, D. (1992). Chemical speciation of nickel in airborne dusts: An analytical method and results of an interlaboratory test program. Environ. Sci. Tech. 26: 138-144.
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