Heavy metal distribution in soils of some urban and peri-urban horticultural farms in Botswana
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Date
2014-07Author
Obuseng, L.C.
Meulenberg, F. Pule
Mubyana, T. John
Mpuisang, T.
Agbenin, J.
Oluko, Patrick Samba
Norton, J.
Okalebo, J.R.
Omondi, E.
N’getich, W.
Shikuku, D.S.
Okeyo, J.M.
Odhiambo, J.A.
Norton, U.
Ashilenje, D.
Wangoli, J.W.
Otiende, Verrah Akinyi
Mwanga, E.F.
Gitau, A.N.
Christiane, T.
Ernest, M.
Manuel, Joana
Matusse, Joaquim
Pimentel, Andréa Eloisa Bueno
Hess, S.
Hatab, A.A.
Da Silva, L.M.
Boly, H.
Glym, C.
Chibinga, O.C.
Musimba, N.M.
Nyangito, M.
Simbaya, J.
Elhag, M. Muna
Sulieman, M. Hussein
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Show full item recordAbstract
Despite the fact that there is high usage of agrochemicals and use of urban waste water for
irrigation, the concentration of potentially toxic metals in urban and peri-urban agriculture
(UPA) farms has not been widely investigated in Botswana. The study focused on quantitative
assessment of potentially toxic metals in horticultural production under UPA. Crops which
are cultivated at the selected study sites include spinach (Spinacia oleracea L.), rape
(Brassica rapa var. rapa.), cabbage (Brassica oleracea var. capitata), green pepper
(Capsicum annum) and tomato (Solanum lycopersicum). Two farms from areas
surrounding Gaborone namely Glenn Valley and Mmankgodi, were sampled for the
determination of total heavy metals concentration in soils. In Glenn Valley secondary treated
waste water is used for irrigation while in Mmankgodi underground water is used. Four soil
profile pits were dug at each farm and soil samples of 20 cm increment were collected from
the surface to a depth of 100 cm. Results showed concentration ranges of 0.12 - 1.22 mg/
L for Cr, 0.09 - 0.47 mg/L for Cu and from 0.01 - 0.24 mg/L for Pb. Copper and Chromium
were above threshold levels for crop production (Cu 0.2 mg/L, Cr 0.1 mg/L) as per Food
and Agriculture (FAO) standards and Botswana Bureau of Standards (BOBs), while Pb
concentration was significantly higher at Glenn Valley than Mmankgodi, but below
recommended threshold levels of 2.0 mg/L. These results are a wake-up call that policies
on the use of sewage effluent and agrochemicals should be enforced.
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