Beyond Total Content: Assessing the Bioaccessibility of Metals in Tattoo Inks Using Validated Extraction Media

Abstract

A validated analytical workflow is presented for determining total and bioaccessible concentrations of regulated elements in tattoo inks, addressing the lack of harmonized protocols for comparing extraction approaches in complex matrices. Although current legislation defines limits for soluble fractions of selected metals, it does not specify the extraction media to be used, despite the heterogeneous composition of tattoo inks potentially affecting metal mobility and release. Total elemental concentrations were determined after microwave-assisted acid digestion, while bioaccessible fractions were assessed using three in vitro extraction media: deionized water, artificial sweat and physiological saline. The analytical performance and reliability of the extraction procedures were validated. Elemental determinations were performed by ICP-MS and CV-AFS. The workflow showed good precision, reproducibility and comparability among extraction media, enabling systematic evaluation of matrix-dependent metal release. Commercial inks exhibited high variability in elemental composition depending on colour and formulation. Lead exceeded regulatory limits in several samples. Yellow inks were enriched in Ba, Cd and Zn, whereas blue inks showed higher concentrations of Cu, As, Pb and Sn. Bioaccessibility strongly depended on the extraction medium (p < 0.05). Nickel reached 63% solubility in saline and 59% in artificial sweat in black inks, while Hg reached up to 72% in white inks. This approach links total elemental content to exposure-relevant bioaccessible fractions and supports more harmonized safety assessment and regulatory monitoring of tattoo inks.