High radon concentrations in artisanal copper-cobalt underground mining in Kolwezi, Democratic Republic of the Congo.

BACKGROUND

Cobalt mining plays a crucial role for the local and national economy of the Democratic Republic of the Congo (DRC), but mining leads to serious occupational health risks, including exposure to radon emanating from the uranium-rich ore in the region. However, no data are available about radon levels in artisanal copper-cobalt underground mines in Kolwezi.

METHODS

Between May 2021 and April 2023, radon concentrations were measured by means of passive diffusive radon detectors (Radonova) in 3 copper-cobalt underground artisanal mines (Kamilombe, Bridon, and Usine à Cuivre de Kolwezi [UCK]). Thirty detectors were deployed for 56 to 84 d.

RESULTS

Of the 30 detectors, only 20 were retrieved because of cave-ins. Median [range] radon levels were 1,425 Bq/m3 [111 to 6,848 Bq/m3] for Kamilombe (n = 10), 2,210 Bq/m3 [96 to 7,910 Bq/m3] for Bridon (n = 5), and 24,800 Bq/m3 [96 Bq/m3-above saturation level of ∼24,000 Bq/m3] for UCK (n = 5). In Kamilombe, radon levels correlated with shaft depth (Spearman ρ = 0·70, P = 0.03).

CONCLUSION

Taking an average duration of 12 h of underground work per day, the observed median radon concentration levels would lead miners to exceed the recommended annual effective dose of 6 mSv within a few months, thus exposing them to a well-recognized risk of lung cancer. Combined with the uranium-rich geology and poor mine ventilation, these findings identify an important occupational health hazard and underscore the need for improved ventilation and routine radon monitoring.