A cross-sectional study assessing mercury exposure and poisoning among workers in informal gold mines in French Guiana

Objectives Informal gold mining represents a major source of mercury pollution worldwide. People involved in informal gold mining in French Guiana are mainly migrants from Brazil and represent an exposed, mobile and hard-to-reach population. This study assessed mercury poisoning in this particular population. Design This multicentre, cross-sectional survey, conducted in 2022, included participants using snowball sampling. Setting Inclusions took place in the logistical rare bases of gold mining at the border between French Guiana and Brazil and French Guiana and Suriname. Participants Between September and December 2022, 539 participants were included in the study. Inclusion criteria were being over 18 years, working in gold mines in French Guiana and having left the mine for less than 7 days. Among them, 526 had a usable blood sample, and 439 had a usable hair sample. Intervention After giving informed consent, the participants received a questionnaire, a medical examination and provided a dried blood spot and a hair sample. Results The median concentration of mercury in hair was 4.5 µg/g (IQR=1.3–9.4), and 46.7% of the study population (205/439) had a concentration above 5 µg/g and 23.7% (104/439) above 10 µg/g. This population is highly exposed to mercury inhalation, with 59.0% performing or witnessing the gold amalgamation process, using minimal protective measures. Piscivorous fish consumption is another potential source of contamination, with 82.0% reporting consumption in the previous month. This digestive source of exposure seems to be associated with mercury hair concentration. We observed a geographical heterogeneity of mercury exposure, with lower levels of poisoning in the eastern part of the region. Higher hair mercury concentrations were found in individuals with a history of malaria attacks and with systolic blood pressure above 160 mm Hg. Conclusion Mercury intoxication in this population is concerning and comparable to levels observed in other Amazonian communities. Physicians treating women working in gold mines should assess mercury concentrations in their hair and provide appropriate guidance. Comprehensive clinical investigations are needed in future studies to accurately assess neuropsychological impacts.