Abstract
Introduction: Untreated wastewater contains heavy metals harmful to human health and the environment. People get access to untreated water through broken sewer pipes, blocked manholes and direct disposal into rivers. One such river is the Ngong River which traverses Nairobi City County and out through the Njiru and Ruai suburbs. Residents who dwell in the slums along the river use untreated wastewater for irrigating their adjacent farms and washing cars as a means to their livelihood. Soils and vegetables grown or irrigated with untreated wastewater may contain high levels of heavy metals that are detrimental to health. The heavy metals may emanate from the waste water discharged by the small scale industries that are based in the study site. However, reports on levels of heavy metals in untreated waste water and soils in Kenya are very scarce. Therefore this study aimed to determine the concentration of Cd, Pb, Zn, Mn, Fe and Cu in the soil and untreated waste water in Ruai and Njiru.
Methodology: Untreated wastewater and soil were collected during the dry season from various sites in Ruai and Njiru from small scale farms along Ngong River. The samples were also obtained from a control plot at the Kenyatta University. The samples underwent wet digestion pre-analysis procedures. The heavy metals were determined by atomic absorption spectroscopy.
Results: The concentrations (mg/L) of the heavy metals in untreated wastewater ranged from 3.09 to 3.54 for Mn, 0.01 to 0.03 for Zn, 0.21 to 0.28 for Pb, 4.79 to 8.07 for Fe, 0.17 to 0.22 for Cu and 0.42 to 0.47 for Cd.All the target heavy metals were found to be present in the soil in all the sites. The concentration ranged from 3194.30 to 3603.26 mg/kg for Mn, 13.56 to 15.05 mg/kg for Zn, 70.40 to 73.29 mg/kg for Pb, 7500.75 to 7534.77 mg/kg for Fe, 40.44 to 41.01 mg/kg for Cu and 22.20 to 23.34 mg/kg for Cd.
Conclusion: From the study, the level of heavy metals in the untreated wastewater affects the concentration of heavy metals in soil. When the untreated wastewater has a high concentration of heavy metals, the soil adsorbs the heavy metals and thus high concentrations in the soils.
Keywords: Heavy metals, Untreated wastewater, Soil, Adsorption.
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Corresponding Author
Scholastica Gatwiri Mathenge
P.O Box: 43844-00100, Nairobi, Kenya
+254722936884, Email: This email address is being protected from spambots. You need JavaScript enabled to view it.
DOI: https://dx.doi.org/10.18535/jmscr/v6i8.124
