“Comparative study of the level of heavy metals in wastewater, sediment and aquatic organisms: a perspective of the tackling environmental threats for the food security, Environmental pollution and their removal using agricultural wastes»

Abstract

The ecological and environmental pollution is due to the deposition or poor disposal of wastes in the ecosystem. The evaluation of pollution may concentrate on various quality indicators like CF (Contamination Factor), Igeo (Geoaccumulation Index), pollution load index (PLI), and bioaccumulation factor (BAF). This study investigated the level of selected heavy metals such as cadmium (Cd), nickel (Ni), Zinc (Zn), copper (Cu), lead (Pb), and chromium (Cr) in wetland ecosystems (case study in Nyabarongo and Nyabugogo). The collected samples, including soil sediments, benthic species, and aquatic organisms, were analyzed for the concentrations of metals were analysed using an Atomic Absorption Spectrophotometer (AAS) according to standard protocols. The results revealed the average concentrations of the metals for waste water, soil sediment vegetables and aquatic organism , for waste water mean Pb (0.79 ± 0.04 ppm), Fe (2.16 ± 0.08 ppm), Mn (0.938 ± 0.11 ppm), Ni (1.034 ±0.02 ppm), Zn (1.33 ± 0.01 ppm), Cu (1.31 ± 0.005 ppm) and Cd (0.272 ± 0.001 ppm) , for the soil sediments Pb (0.52 ± 0.01 ppm), Fe (1.11 ± 0.02 ppm), Mn (1.58 ± 0.01 ppm), Ni (0.69 ±0.02 ppm), Zn (1.75 ± 0.03 ppm), Cu (1.81 ± 0.005 ppm) and Cd (0.172 ± 0.001 ppm) and for fish Pb (1.68 ± 0.04 ppm), Fe (2.26 ± 0.04 ppm), Mn (0.80 ± 0.03 ppm), Ni (1.34 ±0.006 ppm), Zn (1.65 ± 0.06 ppm), Cu (1.41 ± 0.004 ppm) and Cd (0.12 ± 0.007 ppm) and vegetables Pb (0.13 ± 0.01 ppm), Fe (0.36 ± 0.02 ppm), Mn (0.28 ± 0.01 ppm), Ni (0.33 ±0.002 ppm), Zn (0.65 ± 0.001 ppm), Cu (0.71 ± 0.003 ppm) and Cd (0.07 ± 0.001 ppm). Intriguingly, the mean concentration of all measured metals is under the limits, and also is within the permissible limits, comparatively lower than the national and international contexts. Additionally, the assessment gathered on the health risk signified no immediate effect on the group ages taken; meanwhile, all metals are below the threshold impact. These results provide important insights for environmental monitoring and management. The report further emphasizes the critical need for ongoing surveillance and regulation of materials containing heavy metals to protect ecosystems, public health, and food security. Bio-adsorption using rice husk biochar (RHB), which is an environmentally friendly, economical, efficient, and simple technique, was used to treat wastewater, considering various factors such as bio-sorbent dosage, pH, and contact time.The IR spectrum of the adsorbent after treatment exhibited the disappearance or shift of certain peaks, indicating successful adsorption of heavy metals and reflecting the highest percentage of heavy metal removalusing RHB is for 87.56% for Pb2+ and Mn2+ is for 81.40%