Bioaccessibility, corrosion and surface properties of metals, alloys and metallic powder in biological fluids of relevance for occupational and consumer health hazard assessment

Abstract: When assessing hazards of metals, alloys, and metal-containing items, the metal release (bioaccessibility) is of high importance. Triggered by increasingly stricter hazard classifications for metals, especially cobalt (Co), and limited knowledge, the aim of this doctoral thesis is to assess correlations between the metal/alloy surface characteristics, corrosion and metal release pattern in different simulated biological fluids relevant to human exposure scenarios (dermal, ingestion and inhalation, Papers I-V). In addition, occupational alloy powders (additive manufacturing, Paper III) and tattoo inks (Paper VI) were assessed in relation to potential health hazards. A reliable and reproducible in-vitro bioaccessibility test methodology was elaborated (Paper I). Generated nickel (Ni) and Co bioaccessibility data correlates with the surface and corrosion properties of the metals/alloys in the synthetic fluids, suggesting that the bioaccessible concentration, rather than bulk content, should be used for hazard assessment of Ni and Co in alloys and metals (Papers I-IV). Metallic Co was homogeneously distributed along with metallic Ni beneath the surface oxide of stainless steel 316L under different exposure conditions (Paper V). Exposure in a phosphate-containing neutral fluid resulted in the precipitation and incorporation of both Co and phosphate in the oxide (Paper V). Reused alloy powder during laser additive manufacturing processes revealed, depending on alloy type, different physicochemical properties including corrosion properties (Paper III). A large majority of the investigated tattoo inks violated existing regulations on labelling and substances of health concern (Paper VI), and Co, Ni, and other impurities were associated with iron-rich pigments. In all, this thesis presents bioaccessibility findings connected to surface characteristics relevant for hazard assessments of alloys and powders, and points towards physicochemical reasons behind the release of certain metallic impurities.

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