Refinement of post-acidification steps in the unified BARGE method for determination of metal bioaccessibility in consumer products: Addressing precipitation issues

Abstract

Background: Standard Unified BioAccessibility Research Group of Europe (BARGE) Method (UBM) protocols for metal bioaccessibility assessment face challenges due to post-acidification precipitation, causing significant methodological inconsistencies across studies. This research systematically examined precipitate formation by characterizing protein-metal interactions and identifying specific proteins involved, leading to development of an enhanced UBM method for more reliable metal bioaccessibility measurements in consumer products. We focused on precipitation caused by acid injection during sample storage for subsequent instrumental analysis. Results: FT-IR analysis revealed precipitates primarily consisted of albumin with characteristic amide bands. Among 15 tested metals, Ag and Sn showed significant losses (>97 % and >52 %) during filtration due to protein complexation, while others remained unaffected. A modified UBM protocol using complete microwave digestion instead of filtration was validated across six laboratories with robust Z-scores below 2. Applications to commercial toys revealed matrix-dependent Cu variations (12–26 %) despite identical total content. Comparative analysis showed consistently higher metal bioaccessibility in fasted versus fed conditions, providing insights into how physiological conditions influence metal bioavailability. Significance: This study significantly enhances understanding of metal bioaccessibility assessment by revealing protein-metal interactions causing measurement errors, providing crucial methodological improvements that eliminate systematic bias and ensure accurate risk evaluations. These important findings enable better protection of vulnerable populations such as children from contaminated consumer products through more reliable and highly effective hazard identification methods.