Keywords
ecotoxicology
Industrial effluents
N’djili River
Oreochromis niloticus
water quality
How to Cite
Abstract
Introduction
Industrial effluent discharges constitute a major source of aquatic pollution in many developing countries. In Kinshasa, Democratic Republic of the Congo, the REGIDESO water treatment plant at Lemba Imbu discharges effluents directly into the N’djili River, potentially affecting water quality, aquatic organisms, and human health.
Purpose
This study assessed the physicochemical characteristics, lead contamination levels, and ecotoxicological impacts associated with effluents discharged from the REGIDESO Lemba Imbu plant into the N’djili River.
Methods
A field-based cross-sectional study was conducted during the 2025 rainy season in the N’djili Kilambu neighbourhood of Mont-Ngafula Municipality. A total of 45 samples comprising 15 water samples, 15 sediment samples, and 15 specimens of Oreochromis niloticus were collected from three sampling stations (upstream, discharge point, and downstream). Physicochemical parameters including dissolved oxygen, pH, temperature, conductivity, and total dissolved solids were measured. Lead concentrations were determined in water, sediments, and fish tissues. Bioconcentration factors were calculated to evaluate lead accumulation in fish. Data were analysed using one-way analysis of variance, Fisher’s Least Significant Difference test, and Spearman’s rank correlation at a 5% significance level.
Results
Significant spatial variations were observed for all physicochemical parameters (p < .05). Dissolved oxygen concentrations were highest at the discharge point (22.67 ± 7.50 mg/L) and lowest upstream (1.50 ± 0.30 mg/L). Although pH, temperature, conductivity, and total dissolved solids remained within recommended limits, lead concentrations exceeded applicable guideline values in all environmental matrices. Water lead concentrations ranged from 1.008 ± 0.032 mg/L upstream to 1.156 ± 0.008 mg/L at the discharge point. Sediment lead concentrations reached 2.040 ± 0.004 mg/L at the discharge point, while concentrations in Oreochromis niloticus ranged from 7.12 ± 0.22 mg/kg upstream to 12.08 ± 0.08 mg/kg at the discharge point, substantially exceeding the FAO/WHO permissible limit of 0.3 mg/kg. Bioconcentration factors demonstrated significant lead accumulation in fish, with strong positive associations between lead concentrations in water, sediments, and fish tissues.
Conclusion
The findings suggest that effluents discharged from the REGIDESO Lemba Imbu plant contribute to elevated lead contamination and bioaccumulation within the N’djili River ecosystem. Although most physicochemical parameters remained within recommended limits, lead concentrations in water, sediments, and Oreochromis niloticus exceeded applicable environmental and food-safety standards. The observed contamination raises concerns regarding ecosystem health and potential human exposure through fish consumption, highlighting the need for continuous environmental monitoring and improved wastewater management.
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Copyright (c) 2026 Ngub, M. B. E., Kusonika, N. A., Gizanga, V. R., Tangou, T. T., Lusasi, S. W., Mayimbi, K. S., Iyeli, L. P., Ngubuta, B., Biey, M. E.