Gastrointestinal absorption of nickel is relevant to workplace safety and health insofar as the consumption of food or the smoking of cigarettes in the workplace or without adequate hand washing can result in the ingestion of appreciable amounts of nickel compounds.
Intestinal absorption of ingested nickel varies with the type of food being ingested and the type and amount of food present in the stomach at the time of ingestion (Solomons et al., 1982; Foulkes and McMullen, 1986). In a human study where a stable nickel isotope (63Ni) was administered to volunteers, it was estimated that 29-40% of the ingested label was absorbed (based on fecal excretion data) (Patriarca et al., 1997). Serum nickel levels peaked 1.5 and 3 hours after ingestion of nickel (Christensen and Lagesson 1981; Patriarca et al., 1997; Sunderman et al., 1989). In workers who accidentally ingested water contaminated with nickel sulfate and nickel chloride, the mean serum half-time of nickel was 60 hours (Sunderman et al., 1988). This halftime decreased substantially (27 hours) when the workers were treated intravenously with fluids.
Other human absorption studies show that 40 times more nickel was absorbed from the gastrointestinal tract when nickel sulfate was given in the drinking water (27±17%) than when it was given in food (0.7±0.4%) (Sunderman et al., 1989). The rate constants for absorption, transfer, and elimination did not differ significantly between nickel ingested in drinking water and food. The bio-availability of nickel as measured by serum nickel levels was elevated in fasted subjects given nickel sulfate in drinking water (peak level of 80 µg/L after 3 hours) but not when nickel was given with food (Solomons et al., 1982).
Studies in rats and dogs indicate that 1-10% of nickel, given as nickel, nickel sulfate, or nickel chloride in the diet or by gavage, is rapidly absorbed by the gastrointestinal tract (Ambrose et al., 1976; Ho and Furst 1973; Tedeschi and Sunderman, 1957). In a study in which rats were treated with a single gavage dose of a nickel compound (10 nickel) in a 5% starch saline solution, the absorption could be directly correlated with the solubility of the compound (Ishimatsu et al., 1995). The percentages of the dose absorbed were 0.01% for green nickel oxide, 0.09% for metallic nickel, 0.04% for black nickel oxide, 0.47% for nickel subsulfide, 11.12% for nickel sulfate, 9.8% for nickel chloride, and 33.8% for nickel nitrate. Absorption was higher for the more soluble nickel compounds.
Clearly, good industrial hygiene practices should include the banning of food consumption and cigarette smoking in areas where nickel compounds are used and should include requirements for hand washing upon leaving these areas.