Mercury Burden in Blood, Hair, and Nails of Leather-Industry Workers in Sialkot: A Cross-Sectional Biomonitoring Study

Abstract

Background: Mercury (Hg) is a potent neurotoxin with well-documented multisystemic effects, and occupational exposure in leather manufacturing is an emerging public health concern in South Asia. Tanneries utilize chemical processes that can release Hg into the environment, leading to absorption through inhalation, dermal contact, or ingestion. Despite this risk, biomonitoring data from Pakistani tannery workers remain scarce, particularly across multiple biological matrices that reflect both acute and chronic exposure windows. Objective: This study aimed to quantify mercury concentrations in blood, hair, and nail samples of leather-industry workers in Sialkot, Pakistan, compared with community controls, and to evaluate correlations among matrices to characterize short- and long-term exposure dynamics. Methods: A cross-sectional study was conducted among 120 male tannery workers and 60 non-industrial controls. Blood, hair, and nail samples were collected, cleaned, acid-digested, and analyzed using inductively coupled plasma–optical emission spectrometry (ICP-OES). Data were analyzed in SPSS using nonparametric tests and Spearman’s correlations. Results: Median Hg concentrations were significantly higher in workers versus controls for blood (0.20 vs. 0.02 µg/L), hair (0.26 vs. 0.03 µg/g), and nails (0.19 vs. 0.02 µg/g) (all p < 0.001). Strong positive correlations were observed between hair and nail levels (ρ = 0.81), supporting cumulative exposure reflection in keratinized tissues. Conclusion: Leather-industry workers exhibited markedly elevated mercury burdens across all matrices, highlighting occupational exposure and validating hair and nails as reliable long-term biomarkers for Hg surveillance in resource-limited settings