Concentrations of Heavy Metals and Pesticide Residues in Leafy Vegetables and Implications for Peri-urban Farming in Nairobi, Kenya

  • Nancy N. Karanja University of Nairobi
  • Mary Njenga University of Nairobi
  • G.K Mutua University of Nairobi
  • C.J. Lagerkvist Swedish University of Agricultural Sciences
  • E, Kutto University of Nairobi
  • J. J. Okello University of Nairobi
Keywords: food safety, heavy metal concentrations, leafy vegetables, peri-urban, pesticide residue

Abstract

The primary objective of this study was to assess the levels of heavy metals, nitrate, and pesticide residues in kale (Brassicaolaracea var. olecephala), a leafy vegetable. The study was conducted in three peri-urban sites in Nairobi, Kenya, where the use of wastewater irrigation is pervasive. The results indicated elevated levels of boron (B), cobalt (Co), chromium (Cr), copper (Cu), lead (Pb), zinc (Zn) and nickel (Ni) in vegetables irrigated with wastewater in two sites. High loadings of the heavy metals Ni, arsenic (As), Pb, Cr, Cu, and Zn into agricultural soils were demonstrated to be from chicken manure. Nitrate levels were within acceptable daily intakes. Residues of diazinon, cypermethrin, biternol, and profenofos pesticides exceeded permissible maximum residue limits in kale at one site. Study findings suggest that consumers of vegetables grown in wastewater-irrigated soils may ingest significant amounts of heavy metals and pesticides. Considering these findings, reducing heavy metal deposits into soils should be a strategic aim of soil protection policies in Kenya.

Author Biographies

Nancy N. Karanja, University of Nairobi
Professor, Soil Ecology; Director, Microbial Resource Centre
Mary Njenga, University of Nairobi
Post-Doctoral Fellow, University of Nairobi
C.J. Lagerkvist, Swedish University of Agricultural Sciences
Professor of Economics, Swedish University of Agricultural Sciences
E, Kutto, University of Nairobi
University of Nairobi
J. J. Okello, University of Nairobi
University of Nairobi
Published
2012-10-22
How to Cite
Karanja, N., Njenga, M., Mutua, G., Lagerkvist, C., Kutto, E., & Okello, J. J. (2012). Concentrations of Heavy Metals and Pesticide Residues in Leafy Vegetables and Implications for Peri-urban Farming in Nairobi, Kenya. Journal of Agriculture, Food Systems, and Community Development, 3(1), 255–267. https://doi.org/10.5304/jafscd.2012.031.003