Comparison of nickel release in solutions used for the identification of water-soluble nickel exposures and in synthetic lung fluids

Abstract

Chemical speciation of workplace nickel exposures is critical because nickel-containing substances often differ in toxicological properties. Exposure matrices based on leaching methods have been used to ascertain which chemical forms of nickel are primarily associated with adverse respiratory effects after inhalation. Misjudgments in the relative proportion of each of the main fractions of nickel in workplace exposures could translate into possible misattributions of risk to the various forms of nickel. This preliminary study looked at the efficiency of the first step of the Zatka leaching method for accurately assessing the 'water-soluble' fraction of several substances present in nickel production operations, compared to leaching in synthetic lung fluid. The present results demonstrate that for nickel sulfate or chloride, the current Zatka solution is adequate to assess the 'water-soluble' fraction. However, when sparingly water-soluble compounds like nickel carbonates or water-insoluble substances like nickel subsulfide and fine metallic nickel powders are present, the first step of the Zatka method can greatly over estimate the amount of nickel that could be released in pure water. In contrast, the releases of nickel from nickel carbonate, nickel subsulfide, and nickel metal powders in pure water are consistent with their releases in synthetic lung fluid, indicating that deionized water is a better leaching solution to estimate the biologically relevant 'water-soluble' nickel fraction of workplace exposures. Exposure matrices relying mostly on the Zatka speciation method to estimate the main forms of nickel need to be re-evaluated to account for any possible misattributions of risk.

Nickel release and surface characteristics of fine powders of nickel metal and nickel oxide in media of relevance for inhalation and dermal contact

“…However, reported findings in many other studies (Horie et al, 2009;Julien et al, 2011;Kodama et al, 1985Kodama et al, , 1993Kuehn and Sunderman, 1982;Oller et al, 2009;Sunderman et al, 1987;Tanaka et al, 1986) are in line with observations in this study with remarkably lower released amounts of nickel from NiO in deionized water compared with more complexing solutions containing chlorides, citrate, amino acids or proteins.…”

“…The release of nickel from the nickel oxide was 65-2100 times lower compared with the nickel metal powders in ALF, effects evident, though less pronounced in ASW (1-10 times lower). Observed results are in good agreement with literature findings, showing a very low solubility of green NiO samples in biological fluids (Oller et al, 2009;Takahashi et al, 1999). Generated results are consistent with previous investigations of the nickel metal sample N36 (Oller et al, 2009) and lower compared with a different sample of nickel powder of smaller particle size (Kuehn and Sunderman, 1982).…”

“…However, since the testing solutions were not identical, the true effect of loading on the nickel release from this sample cannot be assessed. The effect of particle size was most obvious when comparing a study on NiO nanoparticles (BET area 75 m 2 /g, (Pietruska et al, 2011)) in cell culture medium with other studies on fine micronsized particles in other media (this study, (Oller et al, 2009)). Even though the surface area of the NiO nanoparticles was approximately 300 times larger compared with the powder of this study and the study of Oller et al (2009), the nanoparticles dissolved to a significantly higher extent (a factor of 100-5000 or more).…”

“…The effect of particle size was most obvious when comparing a study on NiO nanoparticles (BET area 75 m 2 /g, (Pietruska et al, 2011)) in cell culture medium with other studies on fine micronsized particles in other media (this study, (Oller et al, 2009)). Even though the surface area of the NiO nanoparticles was approximately 300 times larger compared with the powder of this study and the study of Oller et al (2009), the nanoparticles dissolved to a significantly higher extent (a factor of 100-5000 or more). However, as nanoparticles possess significantly different properties compared to micron-sized particles (Nyborg et al, 1992), e.g.…”

“…The extent of nickel release from nickel metal powders was reported to decrease with higher particle loading (surface area/particle mass to solution volume ratio) due to agglomeration and possibly equilibrium shifts (Hamel et al, 1998;Midander et al, 2006Midander et al, , 2007Turner, 2011). The nickel metal sample (N36) has been tested at two significantly different loadings, 2 g/L (Oller et al, 2009) and 0.1 g/L (this work). However, since the testing solutions were not identical, the true effect of loading on the nickel release from this sample cannot be assessed.…”