Particles, sweat, and tears: A comparative study on bioaccessibility of ferrochromium alloy and stainless steel particles, the pure metals and their metal oxides, in simulated skin and eye contact

Abstract

Ferrochromium alloys are manufactured in large quantities and placed on the global market for use as master alloys (secondary raw materials), primarily for stainless steel production. Any potential human exposure to ferrochromium alloy particles is related to occupational activities during production and use, with 2 main exposure routes, dermal contact and inhalation and subsequent digestion. Alloy and reference particles exposed in vitro in synthetic biological fluids relevant for these main exposure routes have been investigated in a large research effort combining bioaccessibility; chemical speciation; and material, surface, and particle characteristics. In this paper, data for the dermal exposure route, including skin and eye contact, will be presented and discussed. Bioaccessibility data have been generated for particles of a ferrochromium alloy, stainless steel grade AISI 316L, pure Fe, pure Cr, iron(II,III)oxide, and chromium(III)oxide, upon immersion in artificial sweat (pH 6.5) and artificial tear (pH 8.0) fluids for various time periods. Measured released amounts of Fe, Cr, and Ni are presented in terms of average Fe and Cr release rates and amounts released per amount of particles loaded. The results are discussed in relation to bulk and surface composition of the particles. Additional information, essential to assess the bioavailability of Cr released, was generated by determining its chemical speciation and by providing information on its complexation and oxidation states in both media investigated. The effect of differences in experimental temperature, 30 degrees C and 37 degrees C, on the extent of metal release in artificial sweat is demonstrated. Iron was the preferentially released element in all test media and for all time periods and iron-containing particles investigated. The extent of metal release was highly pH dependent and was also dependent on the medium composition. Released amounts of Cr and Fe were very low (close to the limit of detection, <0.008% of particles released or dissolved as iron or chromium) for the alloy particles (ferrochromium alloy and stainless steel), the pure Cr particles, and the metal oxide particles. The released fraction of Cr (Cr/[Cr + Fe]) varied with the material investigated, the test medium, and the exposure time and cannot be predicted from either the bulk or the surface composition. Chromium was released as noncomplexed Cr(III) and in addition in very low concentrations (<3 microg/L). Nickel released was under the limit of detection (0.5 microg/L), except for ultrafine stainless steel particles (<10 microg/L). It is evident that media chemistry and material properties from a bulk and surface perspective, as well as other particle characteristics, and the chemical speciation of released metals have to be considered when assessing any potential hazard or risk induced by sparingly soluble metal or alloy particles.

Chemical Stability of Chromium Carbide and Chromium Nitride Powders Compared with Chromium Metal in Synthetic Biological Solutions

“…Even though a time and pH effect was evident, only less than 0.02% of the total amount of loaded powder was dissolved after 168 hours of exposure, see Figure 5. A higher amount of released chromium from surfaces of chromium-rich surface oxides exposed to solutions of high acidity is consistent with previous studies [1,38].…”

“…A slightly higher release of chromium after long exposure periods may be related to a partial dissolution of chromium(III) oxides observed on the surface of the Cr-C powder by means of XPS, an effect also observed for the Cr-metal powder. The comparison with previously performed identical exposures of Cr 2 O 3 powder in ASW and ALF [1,38] shows higher released amounts of chromium from the Cr-C powder, however, still at very low levels (<0.005% or 0.00002 μg/cm 2 /h). This comparison was relevant since all powders revealed the presence of chromium(III) oxides, primarily Cr 2 O 3 on the surface.…”

“…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][2][3][4][5][6][7][8][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][10][11].…”

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

“…5). This time dependence is also known for other passivating materials, such as stainless steel, in non-complexing solutions and solutions of nearneutral pH (Hedberg et al, 2010b;Midander et al, 2010). As previously discussed, the release of nickel was significantly higher in ALF compared with ASW for all powders, Figs.…”

“…For piercing assemblies, the nickel release limit allowed for the materials to remain in commerce is set to 0.2 lg Ni/cm 2 /week (EN, 2011). Many investigations have therefore focused on assessing the bioaccessibility of different nickel compounds, alloys, powders and/or massive material in artificial sweat (Hedberg et al, 2010b;Lidén and Carter, 2001;Lidén et al, 2008;Midander et al, 2007). Nickel-induced allergies are the most frequent reasons for contact dermatitis in the industrialized part of the world, affecting 15% of females and a few% of males (Lidén and Carter, 2001).…”