Exposure to Toxic Metals (As, Cd, Hg, Pb) in Two Artisanal and Small-scale Gold Mining (ASGM) Areas in Zimbabwe

Abstract Background: People living and working in ASGM areas are exposed to toxic metals such as arsenic (As), cadmium (Cd), mercury (Hg) and lead (Pb). Whereas Hg is purposely used to extract the gold from the ore, the other toxic metals can be liberated from the ore during the mining process. These metals can contaminate drinking water and food and are thus, a source of exposure for people living in these mining areas. However, there is limited to no data about the exposure to toxic metals of people living in ASGM areas. Therefore, the purpose of this study was to conduct biomonitoring of people identifying themselves as artisanal gold miners. Methods: Blood and urine were collected from 207 people living and working in two ASGM areas in Zimbabwe. Hg in whole blood and urine was analyzed by direct mercury analysis, Pb in blood as well as As and Cd in urine were analyzed by GF-AAS. The results were evaluated by descriptive analysis and correlated with the location, age, fish consumption, years living and working in the area. Results: Median As level in urine was 10.0 µg/l (range from below limit of detection to 460 µg/l). Median Cd level in urine was 0.3 µg/l (range from below limit of detection to 11.4 µg/l). Median Hg levels in blood / urine were 2.7 / 5.2 µg/l (range from 0.2 to 167 µg/l / 0.1 to 612 µg/l). Median Pb level in blood was 19.9 µg/l (range from 6.6 to 276 µg/l). As expected, the Hg levels were frequently above international reference values (e. g. NHANES, blood: 34%, urine: 69%). For Pb and Cd, a considerable number of participants (32% and 22% respectively) were above the reference values (NHANES / National Health and Nutrition Examination Survey) and for As 33% of the participants were above the reference value (UBA/ German Environment Agency). Conclusions: Hg levels were, as expected in ASGM areas, mainly above reference and threshold values. A high proportion of As, Cd and Pb levels were also above reference levels. Therefore, the exposure to toxic metals in the two ASGM areas in Zimbabwe is relevant for public health.