Metal contaminants in river water and human urine after an episode of major pollution by mining wastes in the Kasai province of DR Congo

Background. In July2021, the Tshikapa river became heavily polluted by mining wastes from a diamond mine in neighboring Angola, leading to massive killing of fish, disease and even deaths among residents living along the Tshikapa and Kasai rivers. The exact nature of the pollutants was unknown. Methods. In a cross-sectional study, conducted in the city of Tshikapa in August 2021, we enrolled by opportunistic sampling 65 residents (11 children <16y) living alongside the polluted rivers, and 65 control residents (5 children) living alongside the Kasai river upstream from the Tshikapa-Kasai confluence. We administered a questionnaire and obtained river water and spot urine samples for measuring thiocyanate (a metabolite of cyanide) and 26 trace metals (by ICP-MS). Results. Participants from both groups consumed river water. In the area affected by the pollution, most participants had eaten dead fish. Prevalences of reported health symptoms were higher in the exposed group than among controls: skin rashes (52% vs 0%), diarrhea (40% vs 8%), abdominal pain (8% vs 3%), nausea (3% vs 0%). In polluted water, concentrations [median (range)] were only higher for nickel [(2.2(1.4–3.5)µg/L] and uranium [78(71–91)ng/L] than in non-polluted water [0.8(0.6–1.9)µg/L; 9(7–19)ng/L]. In urine, concentrations [µg/g creatinine, median(IQR)] were significantly higher in the exposed group than in controls for lithium [19.5(12.4–27.3) vs 6.9(5.9–12.1)], thallium [0.41(0.31–0.57) vs 0.19(0.16–0.39)], and uranium [0.026(0.013–0.037)] vs 0.012(0.006–0.024)]. Urinary thiocyanate concentrations did not differ. Conclusion. This study after an ecological disaster in DR Congo has documented contamination of river water by nickel and uranium, and high urinary levels of some trace metals among affected riverine populations. However, the exact cause of the massive fish kill and disease among residents remains elusive. The capacity to rapidly investigate toxic pollution events must be increased in the area. Keywords.Trace Metals,mining,Water pollution,Kasai province.