Correlation between gold and mercury in human blood among individuals in northwestern Tanzania

Mercury is a highly toxic metal of major global health concern, with exposure disproportionately affecting low- and middle-income countries (LMICs) where artisanal and small-scale gold mining (ASGM) is common. While mercury exposure has been well documented among mining populations, less is known about exposure in general urban populations.

We analyzed baseline data from 1000 adults enrolled in the Mwanza HIV and Cardiovascular Disease cohort (2015-2019) in northern Tanzania. Blood total mercury (T-Hg) and total gold (T-Au) concentrations were measured from dried blood spots using inductively coupled plasma mass spectrometry. Associations between T-Hg and T-Au concentrations were evaluated using Spearman's rank correlation. Associations between a priori-selected covariates and T-Au concentrations were assessed using multivariable bootstrap linear regression models with 1000 resampling iterations.

All participants had detectable blood mercury levels, with a median T-Hg concentration of 5.02 μg/l, and 7.2% had levels exceeding the World Health Organization toxic threshold of ≥20 μg/l. Detectable T-Au was observed in approximately 60% of participants, with a median T-Au concentration of 0.09 μg/l. In bootstrap multivariable regression analyses, HIV infection was associated with higher T-Au concentrations (median β = 0.28; 95% bootstrap CI 0.12-0.51). T-Hg and T-Au concentrations were moderately positively correlated in Spearman's rank correlation (ρ = 0.45; p < 0.001). After multivariable adjustment, T-Hg remained positively associated with T-Au concentrations (median β = 0.39; 95% bootstrap CI 0.22-0.58).

We found that T-Hg and T-Au were detectable in a general population living near an ASGM site, and associated with each other, suggesting a common source of exposure. Improved characterization of exposure routes is critical for informing targeted interventions to reduce mercury-related health risks in Tanzanian communities.