Hypoxemia and radon exposure during underground work in artisanal cobalt mines

Abstract

<b>Aim:</b> More than half the cobalt (needed for electric vehicles) originates form the southern part of DR Congo, and a substantial part of the cobalt is extracted by artisanal miners. We investigated working conditions and health parameters among cobalt artisanal miners around Kolwezi. <b>Methods:</b> In a cross-sectional study of 85 artisanal miners from two underground mines and 42 from open pits, we obtained socio-demographic and occupational data by questionnaire and measured oxygen saturation (SaO2) by pulse oximetry at four different time points: prior to descent into the shaft or quarry (T1), at 50 minutes in the shaft (T2); upon leaving the shaft (T3) and 10 minutes after having left the shaft (T4). In one underground mine, air radon concentrations (Radonova detectors) were monitored for 75-76 days at 10 different locations. <b>Results:</b> Miners working underground (at depths of 36 to 112 m) were somewhat older (34.8±6.8y) than those working in open pits (32.0±7.6y), and they worked more hours daily (12.6±1.2h) than controls (9.1±0.8h). All participants had SaO2 above 95% at T1 and T4, but SaO2 was below 90% in 25 (29%) underground miners at T2 (lowest value 74 %) and in 5 underground miners at T3. Values of SaO2 decreased linearly with depth of work at T2 (R2=0.14; p&lt;0.0001), and also at T3 (R2=0.08; p=0.0021). Mean radon concentrations correlated with shaft depth (Spearman r = 0.70, p = 0.03). <b>Conclusion:</b> Substantial oxygen desaturation occurred during underground work in a high proportion of artisanal mineworkers. This is indicative of poor ventilation of the mine shafts. In addition to hypoxia, insufficient ventilation also leads to the accumulation of radon and risk of lung cancer.