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\hypersetup{pdftitle={Long"=term Wastewater Irrigation of Vegetable Gardens: Enrichment, Leaching Losses and Balances of Zn and Cd},pdfauthor={Nafiu Abdu, John O. Agbenin, Andreas Buerkert},pdfsubject={Tropentag 2010: Abstract},pdfkeywords={Heavy metals, kano, metal flux, urban agriculture},pdfpagemode=None,colorlinks=true}
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\parbox[b]{13.4cm}{\centering \large{\textbf{Tropentag, September 14-16, 2010, Zurich}}\\[1ex] \Large{``World Food System  ---\\A Contribution from Europe''\\[2ex]}}
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\Large{\textbf{Long"=term Wastewater Irrigation of Vegetable Gardens: Enrichment, Leaching Losses and Balances of Zn and Cd\footnote{\textbf{Contact Address:} Andreas Buerkert, University of Kassel, Organic Plant Production and Agroecosystems Research in the Tropics and Subtropics, Steinstraße 19, 37213~Witzenhausen, Germany, \mbox{e-mail}: \email{tropcrops@uni-kassel.de}}\\[0.8ex]}}
\normalsize{\textsc{Nafiu Abdu$^{1}$, John O. Agbenin$^{2}$, Andreas Buerkert$^{3}$}}
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\begin{itemize*}
\item[]{\small{\textit{$^{1}$Ahmadu Bello University, Department of Soil Science, Nigeria}}}
\item[]{\small{\textit{$^{2}$Ahmadu Bello University, Department of Soil Science, Nigeria}}}
\item[]{\small{\textit{$^{3}$University of Kassel, Organic Plant Production and Agroecosystems Research in the Tropics and Subtropics, Germany}}}
\end{itemize*}
\index[author]{Abdu, Nafiu}
\index[author]{Agbenin, John O.}
\index[author]{Buerkert, Andreas}
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\textbf{Abstract}
\begin{abstract}
\normalsize{
Balances and fluxes of heavy metals (HMs) especially in wastewater irrigated gardens provide important information on agro"=ecosystem contamination, management strategies and sustainability. This study aimed at assessing heavy metal accumulation in soils of vegetable gardens, edible vegetable biomass and annual mass balances of Zinc (Zn) and Cadmium (Cd) resulting from atmospheric deposition and wastewater inputs at the plot scale. Cadmium and Zn concentrations in Kano garden soils attained unsafe levels with concentrations of 2.3--4.8 mg Cd kg$^{-1}$ and 13--285 mg Zn kg$^{-1}$. Inputs of HMs through rainwater, dust and irrigation water were primary contamination sources while crop removal and leaching losses represented major output routes. Irrigation water was the dominant HM source with annual inputs amounting to \mbox{16\,kg} Zn ha$^{-1}$ and \mbox{2.7\,kg} Cd ha$^{-1}$. Dust deposition contributed only \mbox{0.04\,kg} Zn ha$^{-1}$ and 2\,$\times$\,10--\mbox{5\,kg} Cd ha$^{-1}$ annually. Surpluses of Zn and Cd were positive in all gardens and ranged from 1.1--\mbox{15.4\,kg} Zn ha$^{-1}$ and 0.29--\mbox{2.31\,kg} Cd ha$^{-1}$. Heavy metals harvested in vegetables exceeded allowable threshold limits. In amaranth annual total HM inputs reached \mbox{1.7\,kg} Zn ha$^{-1}$ and \mbox{0.003\,kg} Cd ha$^{-1}$ while in parsley annual input of Zn and Cd were up to \mbox{0.9\,kg} Zn ha$^{-1}$ and \mbox{0.001\,kg} Cd ha$^{-1}$. Losses of HMs through leaching ranged from 1.1--\mbox{2.8\,kg} Zn ha$^{-1}$ and 0.2--\mbox{0.3\,kg} Cd ha$^{-1}$ with a high potential for underground water pollution. The high inputs and leaching of Zn and Cd through wastewater irrigation emphasised the urgent need for management practices and legislations that will mitigate the harmful effect of wastewater irrigation to sustain consumer and ecosystem health in Kano. }

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\noindent \textbf{Keywords:} Heavy metals, kano, metal flux, urban agriculture
\index[key]{Heavy metals}
\index[key]{Kano}
\index[key]{Metal flux}
\index[key]{Urban!agriculture}
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