Bioaccessibility of nickel and cobalt in powders and massive forms of stainless steel, nickel- or cobalt-based alloys, and nickel and cobalt metals in artificial sweat

Nickel (Ni) and cobalt (Co) are the most common metal allergens upon skin contact at occupational settings and during consumer handling of metals and alloys. A standardized test (EN, 1811) exists to assess Ni release from articles of metals and alloys in massive forms intended for direct and prolonged skin contact, but no corresponding test exists for other materials such as powders or massive forms of alloys placed on the market or to determine the release of Co, for which only limited data is available. Differences in Ni and Co release from massive forms of a range of common stainless steels and some high-alloyed grades compared to Ni and Co metals were therefore assessed in artificial sweat for 1 week at 30 degrees C according to EN 1811. A comparable modified test procedure was elaborated and used for powders and some selected massive alloys. All alloys investigated released significantly less amount of Ni (100-5000-fold) and Co (200-400,000-fold) compared with Ni and Co metal, respectively. Almost all alloys showed a lower bioaccessible concentration (0.007-6.8 wt% Ni and 0.00003-0.6 wt% Co) when compared to corresponding bulk alloy contents (0.1-53 wt% Ni, 0.02-65 wt% Co). Observed differences are, among other factors, related to differences in bulk composition and to surface oxide characteristics. For the powders, less Ni and Co were released per surface area, but more per mass, compared to the corresponding massive forms.