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DRAFT NEW TEST GUIDELINE Determination of Relative Metal

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DRAFT NEW TEST GUIDELINE Determination of Relative Metal 15 February 2021 1 DRAFT NEW TEST GUIDELINE 2 Determination of relative metal/metalloid release using a simple 3 simulated gastric fluid (0.032 M HCl) 4 INTRODUCTION 5 1. There are several laboratory methods to determine metal/metalloid releases in synthetic 6 fluids from various materials including art materials and toys, but also soils [e.g. (1)(2)(3)]. The 7 US EPA Validated Test Method 1340 (one of SW-846 guidance methods) corresponds to the 8 “in vitro bioaccessibility assay for lead in soil" (4), the validation of an “In Vitro 9 Bioaccessibility Test Method for Estimation of Bioavailability of arsenic from soil and 10 sediment” has also been conducted (5)(6). Some of the in vitro methods have been applied to 11 refine the assessments of human exposures to metals/metalloids in soils and dusts [e.g. 12 (7)(8)(9)(10)]. Yet, until adoption of this Test Guideline, there was no internationally 13 harmonised protocol (e.g., OECD Test Guideline) on how to conduct a cell-free in vitro method 14 using a simulated gastric fluid to generate relative metal/metalloid release data for a broad 15 number of metals and metalloids. However, this Test Guideline does not discuss the regulatory 16 use of the data obtained with the test method. Relevant Competent Authorities may be consulted 17 for that purpose. 18 19 2. This Test Guideline describes how to measure material-specific metal/metalloid release 20 data and calculate relative metal/metalloid releases from materials such as metals and 21 metalloids, inorganic metal compounds and other inorganic complex metal(metalloid)- 22 containing materials [e.g., alloys, pigments, and materials of Unknown or Variable 23 composition, Complex reaction products and Biological materials (UVCBs)] in a simple 24 simulated gastric fluid composed of 0.032 M HCl, pH 1.5 ± 0.1. The main interest of the method 25 resides in comparing metal releases between two or more materials of the same metal/metalloid, 26 i.e., a test and a reference material. The way to select reference materials, and to measure and 27 compare metal releases of a test material relative to the one(s) from (a) reference material(s) is 28 described. This Test Guideline builds upon the experience gained from a round robin study 29 examining the performance of the method when applied to a variety of metal(metalloid)- 30 containing materials (11). 31 32 3. Definitions are provided in Annex 1. 33 34 INITIAL CONSIDERATIONS AND LIMITATIONS 35 4. The relative metal/metalloid release method was evaluated by EURL ECVAM and peer 36 reviewed by its Scientific Advisory Committee (ESAC) (12). The review concluded that the 37 fluid and experimental conditions used are representative of the gastric compartment. This 38 method is not intended to address the full gastrointestinal tract. Rather, it is a simple, 39 reproducible approach intended to maximise the release of metal/metalloid ions for the majority 1 15 February 2021 40 of the tested materials and to allow for the relative assessment of metal release between two or 41 more materials. ESAC considered the method appropriate to assess if a matrix effect occurs in 42 alloys (i.e. whether there is an increased or a decreased relative release of the metal ions from 43 the alloy compared to what is expected from the pure ingredient). The method is applicable to 44 many metals but it should not be used as stand-alone to predict absolute bioavailability after 45 oral intake. All relevant documents regarding the validation and peer review of the method are 46 available in the EURL ECVAM Tracking System on Alternative Methods (TSAR) 47 (https://tsar.jrc.ec.europa.eu/test-method/tm2016-02). 48 49 5. The relative metal/metalloid release method applies to test materials such as certain 50 metals and metalloids, inorganic metal compounds, or complex metal(metalloid)-containing 51 materials (e.g. alloys, UVBCs, pigments), in massive form (≥ 1mm diameter) or powder form 52 (≥ 0.1µm - < 1mm diameter). It can be applied to substances and mixtures. Importantly, this 53 Test Guideline does not apply to nanomaterial1. For nanomaterials, the relative metal/metalloid 54 release method in its current form may not allow for a complete separation of released metal 55 ions from the undissolved nanoparticles to be achieved. 56 57 6. For some metals such as mercury (Hg) and silver (Ag), or certain chemical forms of 58 metals such as antimony (Sb) trichloride (SbCl3) and Sb pentachloride (SbCl5), the results in 59 simulated gastric fluids of low pH (e.g., 0.032 M HCl, pH 1.5 ± 0.1) are unreliable due to 60 precipitation. In the case of Sb, this was observed with the two chemical forms of Sb that are 61 corrosive (SbCl3 and SbCl5), but not with other chemical forms (e.g. Sb metal, Sb oxide). In 62 general, any chemical forms of a metal/metalloid showing precipitation in 0.032 M HCl, are 63 outside the technical applicability domain of this Test Guideline. 64 65 7. The following metals (metalloids) and their compounds have shown that releases in 66 simulated gastric fluid can be measured and are within the technical applicability domain of 67 this Test Guideline: arsenic (As), gold (Au), boron (B), cadmium (Cd), cobalt (Co), chromium 68 (Cr), copper (Cu), iron (Fe), germanium (Ge), indium (In), manganese (Mn), molybdenum 69 (Mo), nickel (Ni), lead (Pb), palladium (Pd), platinum (Pt), rhenium (Re), rhodium (Rh), 70 ruthenium (Ru), selenium (Se), silicon (Si), antimony (Sb) non-corrosive compounds, titanium 71 (Ti), vanadium (V), tungsten (W), zinc (Zn) and zirconium (Zr). Data are not yet available for 72 beryllium (Be). 73 8. Relative metal/metalloid releases between test material and reference material can be 74 used to compare different materials of the same metal/metalloid and to rank them. It can also 75 be used to assess the presence of matrix effects in test materials (e.g., alloys), as matrix effects 76 can affect the expected metal/metalloid release in 0.032 M HCl compared to that expected from 77 the pure metal ingredients. It is required that the exposed surface of the materials or the specific 78 surface area (SSA) be reported since it strongly influences metal release. 79 80 9. For most of the metals and their chemical forms in the technical applicability domain 81 (see paragraph 7), fluids with pH ~1.5 may lead to higher metal ion releases compared to fluids 82 of neutral pH. However, for some of the metals/metalloids within the technical applicability 1 Nanomaterials: natural, incidental or manufactured materials containing particles, in an unbound state or as an aggregate or as an agglomerate and where, for 50% or more of the particles in the number size distribution, one or more external dimensions is in the size range 1 nm-100 nm, as defined by the EU Commission in 2011 (13). 2 15 February 2021 83 domain, releases in 0.032 M HCl (simulated gastric fluid) may be lower than releases in other 84 simulated oral fluids with higher pH, such as intestinal fluid. It is important to be aware of the 85 known cases where metal/metalloid release in this Test Guideline may not be the highest. In 86 the case of Mo, Fe, Si, W and Sb, the release from some of their compounds and alloys may 87 not be the highest in 0.032 M HCl (e.g., Mo from MoO3 and some Mo alloys; Fe from FeMo 88 alloy, Si from FeSi alloy and Al silicate). For these elements, metal/metalloid release tests in a 89 second fluid of neutral pH (or water solubility) can provide information on whether simulated 90 gastric fluid could be an acceptable fluid to generate relative releases for the intended purpose 91 (14, 15, 16, 17, 18). Due to the relative nature of the method, even if acidic conditions provide 92 lower absolute releases, as long as the relative releases from 2 or more compounds in a given 93 fluid are compared (and metal release can be accurately measured), the final outcome may not 94 be significantly impacted from what can be predicted based on more neutral pH fluids. Thus, 95 this set of metals/metalloids can still fall within the applicability domain of the simple simulated 96 gastric fluid (0.032 M HCl) even if the acidic conditions do not represent a worst-case-scenario 97 for metal releases. 98 10. This method determines the release of the metal/metalloid as the concentration of the 99 element. However, the applied analytical method does not determine the form in which the 100 metal is released. For many elements, a single oxidation state will be present at pH 1.5 0.032M 101 HCl. For some elements, for which different oxidation or complexation states may be suspected 102 depending on the exact material, additional information is required to justify whether the metal 103 form released from the test material is the same as for the reference material. Examples of 104 analytical methods to assess speciation are described in paragraph 45. 105 106 PRINCIPLE OF THE TEST 107 11. The method involves the measurement of metal release from powder or massive forms 108 of test and reference materials in a solution of 0.032 M HCl, pH 1.5 ± 0.1 at 37 ± 1 °C, after 109 two hours incubation. The test medium and exposure conditions are chosen to mimic 110 metal/metalloid release in gastric fluid after oral ingestion in humans. 111 Main steps: Samples of the test or the reference materials are added in triplicate (i.e., each 112 sample is added to 3 independent vessels) to a solution of 0.032 M HCl at two different loadings 113 (ratio of volume of test medium to mass of sample, see paragraph 38) and incubated for two 114 hours before separating the metal ion released from the original sample by filtration.
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