Kinuthia et al. 2021 — Heavy metal biomonitoring in Nairobi wastewater using mosquitoes and algae
Wastewater, filamentous green algae (Spirogyra), and mosquitoes (Culex pipiens and other species) from open drainage channels in the Nairobi industrial area, Kenya, were analyzed for Hg, Pb, Cr, Cd, Tl (thallium), and Ni to evaluate their utility as biomonitors of heavy metal pollution. Pb, Cr, and Ni levels in wastewater ranged from 3.08 to 15.31 µg/L, while Tl, Hg, and Cd ranged from 0.05 to 0.12 µg/L; Pb, Cr, Ni, and Cd exceeded WHO, Kenya, and US EPA wastewater limits, but Hg did not. Filamentous Spirogyra algae showed markedly higher metal concentrations than wastewater (Pb 110.62, Cr 29.75, Ni 14.45, Cd 0.44, Hg 0.057 mg/kg), consistent with bioaccumulation. Field mosquitoes showed Pb, Cr, Tl, and Ni levels 1.3-2.4 times higher than laboratory-reared mosquitoes, suggesting metal uptake from contaminated water. The study concludes urban mosquitoes and filamentous algae can serve as biomonitors of heavy metal contamination in wastewater.
Key numbers
Wastewater concentrations: Pb, Cr, Ni: 3.08-15.31 µg/L; Tl, Hg, Cd: 0.05-0.12 µg/L; Pb, Cr, Ni, Cd above WHO/Kenya/US EPA limits; Hg below limits. Spirogyra algae (mg/kg): Pb 110.62, Cr 29.75, Ni 14.45, Cd 0.44, Hg 0.057. Correlation Pb & Hg in algae r(2) = 0.957, p < 0.05; Cd & Cr r(2) = 0.985, p < 0.05. Sampling: 8 sites, 30-day period (August — dry season). Mosquitoes: 95% were Culex pipiens. Note: concentrations are in environmental matrices (wastewater, biota), not food matrices.
Methods (brief)
Wastewater samples collected in triplicates using 350 mL dipper; acidified with HCl and HNO3; ICP-MS for metal analysis. Mosquito larvae collected from drainage channels; adult mosquitoes trapped near factory premises. Algae samples identified as Order Zygnematales, Genus Spirogyra.
Implications
Certification: not directly applicable to food-matrix certification; this is an environmental biomonitoring study in industrial wastewater.
Courses: useful as a case study on biomonitoring approaches for environmental heavy metal monitoring and the role of algae as bioindicators.
App: not applicable.