Relationship between atmospheric and urinary nickel in workers manufacturing electrical resistances using nickel oxide: role of the bioavailability of nickel

The daily concentrations of nickel in total (ie inhalable) andrespirable airborne dust (personal sampling) and in post-shiftand pre-shift urine samples were monitored during five consecutivework days in 20 workers exposed to NiO in a workshop manufacturingelectrical resistances. The individual daily atmospheric nickelconcentrations ranged from 0.5 to 9586 µg Ni/m³ (geometricmean 22.9) for total dust and from 0.2 to 332 µg Ni/m³(geometric mean 3.5) for respirable dust. The results of theurinary excretion of nickel suggested that the occupationally-relatedsystemic absorption of nickel strongly differed in one subject(worker E) compared to the other 19 workers. In the latter groupthe nickel concentration in urine never exceeded 5 µgNi/g creatinine, it did not differ between post-shift and pre-shiftsamples (geometric means: 1.1 versus 1.2 µg Ni/g creatinine),and it was only slightly higher than that measured in a groupof 17 non-exposed subjects (mean 0.5 µg Ni/g creatinine;range 0.1–1.7); furthermore their nickel elimination inurine did not change during the days off or after two weeksof holiday. In worker E, the nickel concentration ranged from21 to 101 µg Ni/g creatinine in post-shift urine, thenext morning (after 16 h) it had dropped on average by 50 percent, it decreased further during the days off, and amountedstill to 4.4 µg Ni/g creatinine after two weeks of holiday.These divergent patterns of elimination of nickel in urine aremost likely related to differences in the nature of exposureto airborne nickel involving both particle size and bioavailabilityof nickel. Worker E was exposed to NiO powder of 1–8 µmparticle size resulting in nickel levels of the respirable fractionon average about 50 times that measured for the 19 other workers(3 µg Ni/m³). Transformation of the initial NiO powderinto particles of 150 to 600 µm size and associated changesin physicochemical properties of NiO in the particles of therespirable fraction may explain why the urinary excretion ofnickel in the 19 workers is hardly influenced by their occupationalexposure to this metal. The pattern of urinary nickel eliminationin worker E, however, most likely reflects very recent exposureto NiO, suggesting that the degree of bioavailability of nickelfrom this particular physicochemical form of NiO powder is muchhigher than that usually accepted for poorly soluble nickelcompounds.