Bioaccessibility of nickel and cobalt in synthetic gastric and lung fluids and its potential use in alloy classification

This study investigated nickel and cobalt ion release from the metals and several alloys in synthetic gastric, as well as interstitial and lysosomal lung fluids. Results were used to calculate the relative bioaccessible concentrations (RBCs) of the metals. Nickel release from SS 316L powder in gastric fluid was >300-fold lower than from a simple mixture of powders of the same bulk composition. Gastric bioaccessibility data showed 50-fold higher metal releases per gram of sample from powder than massive forms. RBCs of nickel and cobalt in the alloy powders were lower, equal, or higher in all fluids tested than their bulk concentrations. This illustrates the fact that matrix effects can increase or decrease the metal ion release, depending on the metal ingredients, alloy type, and fluid, consistent with research by others. Acute inhalation toxicity studies with cobalt-containing alloy powders showed that the RBC of cobalt in interstitial lung fluid predicted acute toxicity better than bulk concentration. This example indicates that the RBC of a metal in an alloy may estimate the concentration of bioavailable metals better than the bulk concentration, and the approach may provide a means to refine the classification of alloys for several human health endpoints. [Display omitted] •Ni and Co ion release in synthetic fluids and in vivo toxicity are not accurately predicted by bulk metal concentration.•Co alloy acute inhalation toxicity correlates better with Co release in interstitial lung fluid than bulk concentration.•Relative Bioaccessible Concentration calculation of metals in alloys uses bioelution data from alloy and reference samples.•Relative Bioaccessible Concentration may be higher or lower than bulk concentration.•Relative Bioaccessible Concentration of metals in alloys can be used in weight of evidence to refine alloy classification.