Tattoo inks available online: impact of extraction medium on bioaccessible elements

Tattoo inks marketed through online platforms represent widely accessible consumer products whose composition may include trace elements of toxicological and regulatory concern. Although current legislation establishes maximum limits for the soluble fraction of selected metals, no standardized extraction medium is specified, potentially leading to variability in the assessment of elemental release from complex pigmented formulations. In this study, commercially available tattoo inks belonging to five color categories were investigated to evaluate how different extraction conditions influence the measured concentrations of regulated elements. Total elemental concentrations were determined after microwave-assisted acid digestion, while extractable concentrations were assessed using three aqueous media: deionized water, physiological saline solution, and artificial sweat (pH 5.5). Elemental analysis was carried out by ICP-MS and CV-AFS following validation of accuracy, precision, and recovery. Substantial variability in total elemental concentrations was observed across colors, reflecting differences in pigment composition and manufacturing formulations. Significant differences (p < 0.05) were observed in the concentrations of metals extracted using different media, indicating that the chemical composition of the extracting solution critically influences elemental mobilization. The comparative evaluation of extraction media revealed matrix-dependent behavior, with certain color groups showing enhanced metal release when extracted with physiological saline or artificial sweat solutions. Overall, the results highlight the analytical relevance of extraction strategy when interpreting soluble metal concentrations in tattoo inks. By systematically comparing extraction conditions in commercially available products, this work supports improved consistency in safety assessment and contributes to the ongoing discussion on harmonized approaches for regulatory monitoring of tattoo inks.