Accumulation of toxic metals in sediments and oligochaetes around urban uncontrolled landfills in Kinshasa, DR Congo

Auteur(s): Akonga Marie-Madeleine, Gizanga Rene, Musibono Dieudonné, Carvalho Fernando, Poté John, Atibu Emmanuel
Nom de la revue/Journal: Environmental Geochemistry and Health
Mois: janvier
Volume: 48
Numéro: 3
Année: 2026
DOI: https://doi.org/10.1007/s10653-026-02980-9

DOI : https://doi.org/10.1007/s10653-026-02980-9

Résumé

Urban uncontrolled landfills in Kinshasa generate metal-rich leachates that contaminate sur- rounding freshwater streams, sediments, and biota. To assess the extent of this contamination, sediment from six freshwater streams in Kinshasa (N’djili, Limete, Lemba, Selembao, Mont-Ngafula, Makala) were analyzed to assess contamination by heavy met- als—including Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Mo, Cd, Sn, Sb, Pb and Hg—and bioaccumula- tion in terrestrial (Lumbricus terrestris) and aquatic (Tubifex tubifex, Nais elinguis, Enchytraeus albidus) oligochaetes. Sediments were digested following the Swiss Federal Soil Ordinance (OSol 814.12) and ana- lyzed using ICP-MS for metals and a Direct Mercury Analyzer (CV-AAS) for total Hg. Oligochaete tissues were freeze-dried, acid-digested (HNO3–HClO4), and analyzed using the same instrumentation. Sedi- ment pollution levels were assessed using the Geo- accumulation Index (Igeo), Enrichment Factor (EF), contamination factor (CF), and the overall Ecologi- cal Risk Index (RI), while ecological thresholds were compared to the Canadian Sediment Quality Guide- lines. Bioaccumulation factors (BAF) were calculated to quantify metal transfer from sediments to organ- isms. Sediments showed strong contamination at landfill-impacted sites, with Hg reaching 3.8 mg·kg−1 dry weight—far exceeding Canadian SQGs (TEL: 0.17 mg·kg−1) and PELs (0.486 mg·kg−1). Cu and Zn were also highly elevated (up to 687.9 and 995.3 mg·kg−1, respectively). RI values were highest at Limete (1014–3552.7), indicating very high eco- logical risk. Aquatic oligochaetes exhibited greater bioaccumulation than terrestrial species, with Hg up to 0.876 mg·kg−1 and Cu up to 93.1 mg·kg−1. High BAFs were observed, particularly for Cd (118.2 at Mont-Ngafula) and Sn (263.1 at Makala), confirming strong sediment-to-organism transfer. Fine, organic- rich sediments and proximity to landfill leachates were positively correlated with metal contamination and bioavailability.