Heavy Metals and Trace Elements Contamination Risks in Peri-Urban Agricultural Soils in Nairobi City Catchment, Kenya
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Date
2023
Authors
Agassin Ahogle, Arcadius Martinien
Letema, Sammy
Schaab, Gertrud
Ngure, Veronica
Mwesigye, Abraham R
Korir, Nicholas K
Journal Title
Journal ISSN
Volume Title
Publisher
Frontiers
Abstract
Introduction: With urbanization and industrialization in the developing world,
urban and peri-urban agriculture is increasingly contributing to urban food
systems, employment, and income generation opportunities. However,
urbanization and industrialization may release harmful pollutants, including
heavy metals and trace elements into agricultural soils, posing ecological,
environmental and public health concerns. This paper assessed the potential
risks of soil contamination with heavy metals and trace elements in peri-urban
farmlands in Nairobi city catchment in Kenya.
Methods: A total of 60 soil samples were collected from ten vegetable farming
zones (S1-S10) and processed following standard protocols. The
concentrations of As, Cd, Co, Cr, Cu, Fe, Hg, Mn, Ni, Pb, V and Zn were
analyzed in the samples using inductively coupled plasma-mass spectrometry
(ICP-MS).
Results and discussion: Results revealed that the soil samples have elevated
concentrations of As, Cd, Co, Cr, Cu, Fe, Hg, Mn, Ni, Pb, V and Zn, with some
elements including As (1.7%), Cd (13.3%), Mn (80%), Pb (1.7%) and Zn (11.7%)
exceeding the permissible thresholds for agricultural soils. The spatial
distribution of the elements exhibited three similar distribution patterns with
slight variations between the hotspot sites of the different elements: (i) Co and
Mn, (ii) Cu and Cr and (iii) As, Cd, Fe, Hg, Pb and Zn, while Ni and V exhibited
singular spatial distributions compared to other elements. Elements such as As,
Cd, Co, Fe, Hg, Mn, Pb and Zn appeared to be of anthropogenic enrichment, while Cr, Cu, Ni and V appeared to originate mainly from lithogenic and natural
sources. The elements As, Cd, Hg and Pb exhibited high ecological risks, with
Cd contributing about 46-66% of the overall ecological risk. The sampling sites
S1, S5, S7, S9 and S10 depicted the highest ecological risks of 145, 103, 146, 121
and 146, respectively. The findings call for proper zoning of suitable agricultural
areas and sound waste management protocols in urban and peri-urban
landscapes. Further, remediation of contaminated soils and farmers’
sensitization are recommended for ecological and public health risk alleviation.
Description
Article
Keywords
peri-urban agriculture, wastewater irrigation, ecological risk, soil pollution, food safety, spatial distribution
Citation
Ahogle, A. M. A., Letema, S., Schaab, G., Ngure, V., Mwesigye, A. R., & Korir, N. K. (2023). Heavy metals and trace elements contamination risks in peri-urban agricultural soils in Nairobi city catchment, Kenya. Frontiers in Soil Science, 2, 76.