<b>Blood, Hair, and Nail as Biomarkers of Arsenic Exposure among Leather Industry Workers in Sialkot</b>

Background: Leather processing involves inorganic chemicals that can elevate arsenic exposure, yet the biological matrix that best discriminates occupational uptake remains uncertain in resource-constrained settings. Objective: To compare whole blood, scalp hair, and fingernail arsenic for their ability to distinguish tannery workers from non-exposed adults and to appraise matrix performance for surveillance. Methods: In a cross-sectional comparative study, 40 workers from five Sialkot tanneries and 40 community controls provided venous blood, proximal hair, and fingernails for ICP-OES quantification under blinded QA/QC. Group contrasts used Welch’s tests with Hedges’ g and Holm-adjusted p-values; robustness was examined with age- and tenure-adjusted linear models. Results: Blood showed the clearest separation (mean workers 0.246 µg/dL vs controls 1.622 µg/dL; Hedges’ g −0.53, 95% CI −0.90 to −0.16; unadjusted p=0.020, Holm p=0.061). Hair indicated a smaller, imprecise difference (−1.397 vs 1.728 µg/g; g −0.44, 95% CI −0.86 to −0.03) with marked variance inflation (SD ratio ≈10.1), and nails showed minimal discrimination (1.834 vs 1.443 µg/g; g +0.26, 95% CI −0.11 to 0.63). Conclusion: Whole blood provides the most reliable, clinically actionable indicator of arsenic exposure in this workforce, whereas keratin matrices require larger samples and stringent decontamination to stabilize inference; integration of blood arsenic into routine occupational surveillance is supported.