Apart from unusual sources, such as massive nickel in meteorites, nickel from natural sources is usually found at modest concentrations and occurs in conjunction with a wide variety of other metals and non-metals. Although nickel is a ubiquitous metal in the natural environment, industrialization has resulted in increased concentrations of nickel in both rural and urban environments.
Nickel-bearing particles are present in the atmosphere as constituents of suspended particulate matter and, occasionally, of mist aerosols. The primary anthropogenic stationary source categories that emit nickel into ambient air are: (1) combustion and incineration sources (heavy residual oil and coal burning units in utility, industrial, and residential use sectors, and municipal and sewage sludge incinerators), (2) high temperature metallurgical operations (steel and nickel alloy manufacturing, secondary metals smelting, and co-product nickel recovery), (3) primary production operations (mining, milling, smelting, and refining), and (4) chemical and catalyst sources (nickel chemical manufacturing, electroplating, nickel-cadmium battery manufacturing, and catalyst production, use, and reclamation). Typical ambient air concentrations of nickel range from 0.03 (North Sea remote site) to 21 ng Ni/m3 (industrially influenced site) (Working Group on As, Cd and Ni Compounds, 2001).
In aquatic systems, such as in ambient or drinking water, nickel is usually present as the nickel cation (Ni2+), together with other anions such as hydroxyl (OH-), sulfate (SO42-), chloride (Cl-), carbonate (CO32-), or nitrate (NO3-). Sources of nickel in ambient waters include chemical and physical degradation of rocks and soils, deposition of atmospheric nickel-containing particulate matter, and discharges from industrial processes. The recently completed EU Risk Assessment of Nickel reported ambient dissolved nickel concentrations for typical European freshwater systems ranging from 1 to 6 µg Ni/L. Higher and lower concentrations may be encountered in waters with specific geological influences, but nickel concentrations for most freshwater systems will fall within this general range. Nickel levels in soil vary between 5 and 500 µg Ni/g depending on geological factors.
For purposes of this document, however, the main concern is nickel presence in occupational settings. The use of nickel, although concentrated in the traditional uses of stainless steels and high-nickel alloys, continues to find new uses based on magnetic, catalytic, shape-memory, electro-magnetic shielding, electrical, and other esoteric properties. Thus more nickel in small quantities and in various forms will be used in more industries and applications. The contributions being made by nickel have never been greater but neither has the need for an understanding of nickel.
It is evident that industrial processes present potential for exposure of workers to higher concentrations of nickel and/or its compounds than those generally found in the natural environment. Occasionally, these exposures may be to a refined form of nickel, but usually they are mixed, containing several nickel compounds and/or contaminants. These “mixed exposures” often complicate the interpretation of health effects of specific nickel species.