Chromium carbide (Cr-C) and chromium nitride (Cr-N) powders were compared with a chromium metal powder (Cr-metal) to evaluate their chemical stability in solution. All three powders were exposed in five different synthetic biological solutions of varying pH and chemical composition simulating selected human exposure conditions. Characterisation of the powders, using GI-XRD, revealed that the predominant bulk crystalline phases were Cr7C3 and Cr2N for Cr-C and Cr-N respectively. The outermost surface of Cr-C, determined by XPS, contained Cr7C3 and Cr2O3 and the corresponding measurement on Cr-N revealed Cr2N and CrN apart from Cr2O3. The presence of Cr2O3 was verified by XPS investigations of the Cr-metal powder. The mean particle size was similar for Cr-metal and Cr-N but slightly smaller for Cr-C. All three powders were poorly soluble and released very low amounts of chromium (<0.00015？μg Cr/μg loaded particles) independent on test solution. Slightly higher chromium concentrations were determined in the more acidic media (pH 1.7 and 4.5) compared with the near-neutral solutions (pH 7.2 and 7.4). Cr-C released the lowest amount of Cr despite having the largest surface area a feature attributed to the strong covalent bonds within the matrix. 1. Introduction Chromium metal and chromium compounds are used in a wide variety of applications ranging from alloying to tanning of animal hides to pigmentation. The extensive use raises questions concerning the potential adverse effect on human health and on the environment. Within the European Community regulatory frame work, REACH, (Registration, Evaluation, Authorization and Restriction of Chemicals), the responsibility to ensure that all products are safe for use lies on the industry and they are consequently required to provide information on the product properties to allow safe handling. Elaborate studies have been performed generating data on release, dissolution, and solubility aspects of chromium and chromium-containing alloys such as stainless steels and ferrochromium alloys [1–9], data that has been utilised within the framework of the European chemicals legislation (REACH) implemented in 2007. Bioaccessibility and environmental impact aspects of chromium have been discussed by, for example, [9–11]. Dissolution studies concerning chromium-containing materials like chromium carbide and chromium nitride are, however, much scarcer and have not been performed with the purpose to evaluate interactions with the environment or the human body [12, 13]. Both chromium carbide and chromium nitride are commonly used
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