Chromium (Cr) remains a significant environmental health concern, with exposure mainly through ingestion and inhalation. Its toxicological profile is driven by oxidation state: trivalent chromium Cr(III) shows low bioavailability, whereas hexavalent chromium Cr(VI) is highly bioavailable, crosses cell membranes, and generates reactive intermediates associated with oxidative and genotoxic effects. Several studies have highlighted the assessment of chromium exposure, particularly Cr(III) and Cr(VI), across different biological matrices as a key approach for accurate exposure characterization. This review synthesizes experimental and epidemiological evidence regarding urinary chromium (uCr) as a biomarker of exposure, alongside advances in analytical techniques and the emerging exposome framework. Although widely used due to non-invasive sampling and suitability for large studies, uCr primarily reflects recent exposure (<48 h), exhibits high intra- and inter-individual variability, and lacks routine Cr(VI)/Cr(III) speciation, limiting its value for low-level environmental exposure. Unlike urinary or whole blood chromium, chromium in red blood cells (RBCs) is specific to Cr(VI) exposure, since in vitro studies reveal selective, donor-independent accumulation of hexavalent chromium in RBCs. However, the current literature is primarily concerned with sampling strategies, pre-treatment procedures, and analytical validation, with comparatively little consideration given to chromium speciation and species interconversion in biological matrices, despite their essential significance for exposure assessment and toxicological interpretation.
Georgaki et al. (Tue,) studied this question.