Sustainability of artisanal mining of cobalt in DR Congo

Abstract

The sustainability of cobalt is an important emerging issue because this critical base metal is an essential component of lithium-ion batteries for electric vehicles. More than half the world's cobalt mine production comes from the Katanga Copperbelt in DR Congo, with a substantial proportion (estimated at 15-20%) being extracted by artisanal miners. Here we show, in a case study performed in the town of Kolwezi, that people living in a neighbourhood that had been transformed into an artisanal cobalt mine, had much higher levels of cobalt in urine and blood than people living in a nearby control area. The differences were most pronounced for children, in whom we also found evidence of exposure-related oxidative DNA damage. It was already known that industrial mining and processing of metals have led to severe environmental pollution in the region. This field study provides novel and robust empirical evidence that the artisanal extraction of cobalt that prevails in the DR Congo may cause toxic harm to vulnerable communities. This strengthens the conclusion that the currently existing cobalt supply chain is not sustainable.

Figure 1. Satellite images of Kolwezi and the study area

Upper panel: satellite image (Google Earth) of the Kolwezi area with its urban residential zone (within white dashed line) and the zone of industrial mining to the West of the town. The study area (within yellow dashed line) is shown in detail in the lower panel. Lower panel: study area showing the chosen control area without mining activities (on the right circled by a green dashed line) and the approximate area affected by artisanal mining (on the left circled by a red dashed line). The red and green dots with letters A to N indicate the 14 plots where participants were recruited. Zones of reddish coloration within the mining area are due to orange plastic sheeting used for sheltering or covering mine pits (Imagery date is 5/6/2016). The white horizontal line corresponds to 1000 m.

Figure 2. Concentrations of trace elements in surface dust and ore

Left panel: concentrations of trace elements, ranked by their abundance in 3 samples of ore (grey bars), surface dust from the mining (exposed) area (9 plots, red bars) and the control area (5 plots, green bars); bars represent the range of values with mean (for some elements, green bars are partially or totally hidden behind another bar). Right panel: Ratio of geometric mean (GM) concentrations of metals in surface dust from the exposed area over the control area (y-axis) against ratio of GM concentrations of metals in ore over control surface dust (x-axis). Confidence intervals of GM ratios can be found in Supplementary Table 1. Full symbols indicate both GM ratios are significantly higher than 1, half-filled symbols indicate GM ratio differs significantly from 1 only for ore/control (symbol divided horizontally) or only for exposed/control (symbol divided vertically). Spearman correlation coefficient for the 20 data points is 0.85 (95% CI 0.65–0.94, p<0.0001)]

Figure 3. Concentrations of cobalt, uranium and manganese in urine (left), and of cobalt and manganese in blood (right).

Data from residents in the control area are shown in green (open); data from residents in the mining area are shown in red (filled); data from mineworkers (diggers) are shown in black. Uranium was below detection limits in blood. Box plots with medians and 25^th-75^th percentiles, and 10^th-90^th percentiles for whiskers; numbers of subjects in each group are indicated at bottom of graph. * p<0.05, ** p<0.01, *** p<0.001 for comparison with control subjects (adults or children, as appropriate); ^# p<0.05, ^## p<0.01 for comparison with exposed adult residents (see Supplementary Tables 4 and 6 for details).

Figure 4. Relation between concentrations of cobalt and 8-hydroxydeoxyguanosine (8OHdG) in urine

Individual data from adult residents (left panel) and children (right panel). Data from residents in the control area in green open symbols, data from residents in the mining area in red filled symbols. Note logarithmic scale of x-axis and y-axis. Spearman correlation is nonsignificant among adults (rho=0.23; 95%CI -0.25–0.62) and highly significant among children (rho=0.78; 95%CI 0.46–0.92; p<0.001).