For some metals, biological monitoring of urine, blood, and other tissues or fluids may provide a reasonable estimate of exposure which is predictive of health risks. This has not been shown to be the case for nickel (Sunderman et al., 1986). While urinary and blood nickel levels provide a reasonable estimate of recent exposure to soluble nickel compounds and fine nickel metal powders, they do not provide a reliable measure of exposure to other less soluble forms of nickel, nor do they truly provide a reliable measure of total body burden. Rather, they provide an integrative measure of the nickel that has been absorbed in the body from all routes of exposure (inhalation, dermal, and oral). Furthermore, with the exception of nickel carbonyl gas (see below), no consistent correlation has been found between nickel concentrations in biological media and increased health risks following exposure to either soluble or insoluble nickel compounds. Assessments of workplace exposure to inhalable aerosols are likely to reflect health risks better than consideration of nickel levels in urine or plasma (Werner et al., 1999). Hence, for the most part, of blood and urinary nickel concentrations are not recommended as surrogates of nickel exposure or nickel- associated health risk.
That said, biological monitoring does provide additional exposure information on an individual and group basis, and also an assessment of the effectiveness of control measures to protect the worker. It can provide reassurance to workers that control measures do work and that they are not absorbing an excessive amount of a potentially harmful substance from the workplace (White, 2001). It can also be used as an education tool for good personal hygiene. It is mainly useful in situations where exposures are to soluble nickel compounds, nickel metal powder, or nickel carbonyl. It is less useful in situations where exposures are predominantly to water insoluble compounds or where exposures are mixed.
Three factors are key to a successful biological monitoring strategy (White, 2001). They are:
- Appropriate Sampling – correct sample type, proper sample timing of sample collection, and avoidance of contamination.
- Accuracy of Measurement – use of validated methods of analysis and quality assurance procedures.
- Interpretation of Results – knowledge of the chemical and physical characteristics of the substance, routes of exposure and uptake, metabolism and excretion and biological limit values.
If a biological monitoring program is implemented, it should augment an environmental monitoring program, so that the biological monitoring information alone is not used as a surrogate of exposure. Both programs should be implemented in conjunction with an industrial hygiene program. In the past, health-based limits of permissible nickel concentrations in blood or urine5 of individuals or groups of workers exposed in either the using or producing industries were lacking due to a paucity of quantitative information on dose-response relationships between these parameters and nickel toxicity (Sunderman et al., 1986). However, some regulatory bodies are now attempting to set Biological Limit Values (BLVs) for nickel and nickel compounds in conjunction with Occupational Exposure Limits (OELs), despite the fact that the utility of setting BLVs for nickel has been questioned by some (Werner et al., 1999). Both OELs and BLVs are discussed in more detail in Chapter 9. It is worth noting that there are no established guidelines for how frequently one should monitor workers, although preliminary recommendations are made below.
Nickel in Urine
Nickel in Blood