Bioaccumulation of metals and metalloids in soils and in the earthworm <i>Hyperiodrilus</i> <i>africanus</i> from uncontrolled landfills in Kinshasa, Democratic Republic of the Congo

To better understand the ecological impact of pollutants from uncontrolled landfills and to assess the potential risks they pose to terrestrial ecosystems and public health, soil samples were collected from uncontrolled landfills in three municipalities of Kinshasa and analyzed for 17 metals and metalloids (including metals Fe, Zn, Mn, Cu, Pb, Cr, Co, Sn, Ni, Cd, Sc, Ag, Mo, and Hg, and metalloids Se, As, Sb) using ICP-MS and AAS. The following decreasing order of elemental concentrations was generally observed in soils: Fe > Zn > Mn > Cu > Pb > Cr > Co > Sn > Ni > Cd > Se > As > Sb > Sc > Ag > Mo > Hg. The Geoaccumulation Index (Igeo) and the Enrichment Factor (EF) indicated very severe to extremely severe soil contamination by metals, with high enhancement of Cu, Zn, As, Ag, Cd, Sb, Pb, and Hg concentrations. Furthermore, several ecotoxicological indices, such as the Potential Ecological Risk Index (RI), highlighted serious soil pollution, particularly in the samples from the landfill receiving industrial waste at Limete municipality. Therefore, the use of these soils from uncontrolled landfills for fertilization of agricultural fields, as farmers currently do, poses a serious risk to public health. Concentrations of metals and metalloids were determined also in the earthworm Hyperiodrilus africanus, collected in the same areas, and the earthworm bioaccumulation factor (on a dry weight basis) displayed values greater than one in most samples and up to 15.3. This bioaccumulation of metals and metalloids from the soil suggests that earthworms can be used as a bioremediation agent for contaminated soils. Based on the results from this research, several recommendations are made to improve the pollution control and to protect public health.