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<p>Urban uncontrolled landfills in Kinshasa generate metal-rich leachates that contaminate surrounding 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 metals—including Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Mo, Cd, Sn, Sb, Pb and Hg—and bioaccumulation in terrestrial (<i>Lumbricus terrestris)</i> and aquatic (<i>Tubifex tubifex</i>, <i>Nais elinguis</i>, <i>Enchytraeus albidus</i>) oligochaetes. Sediments were digested following the Swiss Federal Soil Ordinance (OSol 814.12) and analyzed using ICP-MS for metals and a Direct Mercury Analyzer (CV-AAS) for total Hg. Oligochaete tissues were freeze-dried, acid-digested (HNO<sub>3</sub>–HClO<sub>4</sub>), and analyzed using the same instrumentation. Sediment pollution levels were assessed using the Geoaccumulation Index (Igeo), Enrichment Factor (EF), contamination factor (CF), and the overall Ecological Risk Index (RI), while ecological thresholds were compared to the Canadian Sediment Quality Guidelines. Bioaccumulation factors (BAF) were calculated to quantify metal transfer from sediments to organisms. Sediments showed strong contamination at landfill-impacted sites, with Hg reaching 3.8&#xa0;mg·kg⁻<sup>1</sup> dry weight—far exceeding Canadian SQGs (TEL: 0.17&#xa0;mg·kg⁻<sup>1</sup>) and PELs (0.486&#xa0;mg·kg⁻<sup>1</sup>). Cu and Zn were also highly elevated (up to 687.9 and 995.3&#xa0;mg·kg⁻<sup>1</sup>, respectively). RI values were highest at Limete (1014–3552.7), indicating very high ecological risk. Aquatic oligochaetes exhibited greater bioaccumulation than terrestrial species, with Hg up to 0.876&#xa0;mg·kg⁻<sup>1</sup> and Cu up to 93.1&#xa0;mg·kg⁻<sup>1</sup>. 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.</p>

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

  • 期刊论文

  • 发表日期：

    2026年1月29日

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  • Marie-Madeleine O. Akonga,
  • René V. Gizanga,
  • Dieudonné E. Musibono,
  • Fernando P. Carvalho,
  • John Poté,
  • Emmanuel K. Atibu

摘要

Urban uncontrolled landfills in Kinshasa generate metal-rich leachates that contaminate surrounding 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 metals—including Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, As, Mo, Cd, Sn, Sb, Pb and Hg—and bioaccumulation 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 analyzed 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. Sediment pollution levels were assessed using the Geoaccumulation Index (Igeo), Enrichment Factor (EF), contamination factor (CF), and the overall Ecological Risk Index (RI), while ecological thresholds were compared to the Canadian Sediment Quality Guidelines. Bioaccumulation factors (BAF) were calculated to quantify metal transfer from sediments to organisms. 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 ecological 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.