Variation in thyroid hormone levels is associated with elevated blood mercury levels among artisanal small-scale miners in Ghana

Background: Mercury can be very toxic to human health even at low dose of exposure. Artisanal small-scale miners (ASGMs) use mercury in gold production, hence are at risk of mercury-induced organ dysfunction. Aim: We determined the association between mercury exposure, thyroid function and work-related factors among artisanal small-scale gold miners in Bibiani-Ghana. Method: We conveniently recruited 137 consenting male gold miners at their work site in Bibiani-Ghana, in a comparative cross-sectional study. Occupational activities and socio-demographic data of participants were collected using a questionnaire. Blood sample was analysed for total mercury and thyroid hormones. Results: Overall, 58.4% (80/137) of the participants had blood mercury exceeding the occupational exposure threshold (blood mercury ≥5μg/L). T3(P<0.0001) and T4(P<0.0001) were significantly reduced among the exposed group compared to the non-exposed. TSH showed no significant variation between the exposed and non-exposed groups. Longer work duration (≥5years), gold amalgamation, gold smelting and sucking of excess mercury with the mouth were associated with increased odds of mercury exposure. Blood mercury showed negative correlation with T3(r = -0.29, P<0.0001), and T4(r = -0.69, P<0.0001) and positive correlation with work duration (r = 0.88, P<0.001). Even though a positive trend of association between blood mercury and TSH levels was recorded, it was not significant (r = 0.07, P = 0.4121). Conclusion: Small scale miners in Bibiani are exposed to mercury above the occupational threshold which may affect thyroid hormone levels.