Multi-matrix biomonitoring of human exposure to extreme levels of atmospheric mercury in urban artisanal gold mining areas: A Colombian case study.

Artisanal and small-scale gold mining (ASGM) is the largest anthropogenic source of atmospheric mercury (Hg) globally, yet residential airborne Hg data and associated health impacts remain scarce in urban ASGM settings. The Atrato River basin combines intense ASGM activity with fish-dependent communities, making it a priority region for exposure assessment. We assessed (i) seasonal airborne elemental Hg (THg-Air) in urban Quibdo (QO) and rural Negua (NA); (ii) urinary total Hg (THg-U), hair total Hg (THg-Hair), and hair methylmercury (MeHg-Hair); and (iii) the relative contributions of inhalation and diet using correlation and multiple linear regression. Airborne Hg was monitored at 68 sites across dry and rainy seasons (n = 4608 readings). Biomarkers were analyzed in 127 residents (QO: n = 77; NA: n = 50). Mean THg-Air in QO exceeded international guidelines at 64% of sites (8.40 and 7.85 μg/m3 in dry and rainy seasons), with gold-shop peaks >50 μg/m3, whereas NA levels were ∼100-fold lower. THg-U was significantly higher in QO (10.66 vs. 3.25 μg/L, p < 0.05), and 40% exceeded biomonitoring thresholds. MeHg accounted for ∼80% of hair Hg, reflecting dietary fish exposure. THg-Air correlated strongly with THg-U (r = 0.73-0.88), while hair biomarkers correlated with fish intake (r ≈ 0.47). Sex was the dominant hair-biomarker predictor (β ≈ 0.38), and occupational effects on THg-U emerged only through interaction terms. QO ranks among the most airborne-mercury-contaminated urban environments globally. Dual exposure pathways-inhalation of elemental Hg and dietary MeHg-affect workers and the general population respectively. Multi-matrix biomonitoring is essential, and urgent regulatory action is needed to protect vulnerable communities.