Bioaccessibility testing (Bioelution) of metals, inorganic metals compounds and metals-containing materials: simulated gastric fluid

The bioelution test measures the fraction of a substance that dissolves under surrogate physiological conditions (i.e. simulated gastric fluid) and is potentially available for absorption into systemic circulation (bioaccessible concentration). This test method is not a toxicity test.

The test submitter proposed to use the method in a compartive manner (target and reference material) to generate relative bioaccessible metal ion data for the oral route of exposure, which they consider relevant to systemic effects of metal-containing materials. The relative results obtained could be used to make predictions of how the test material will behave compared to the reference material, based on relative metal ion release. This assumes that the dissolved metal ion is the cause of toxicity.

The test method was then proposed to support read across and grouping under REACH for systemic endpoints and to assign CLP classifications. In the context of hazard classification, the test method has been proposed as a refinement to the current approach to alloy classification. Alloys are defined as special preparations under REACH in recognition of the fact that they do not behave as simple mixtures (EC, 2006). Thus, the rationale is that the gastric bioaccessible concentration of a metal in an alloy appears more informative and then relevant for predicting the toxicity than simply using the concentration of the metal ingredient.

The systemic toxicity of most metals and metalloids is associated to a large degree with the release of soluble metal ions and their uptake by the body and/or interaction at their target organ sites (i.e., the bioavailability of the metal ions). The simple presence of a metal or inorganic ion in a substance does not necessarily impart to that substance the biological properties of the metal/inorganic ion; it is the bioavailability of the ion at the site of action in the organism that is the most important factor determining toxicity for metals and minerals.