Etude des métaux lourds dans les sols, eaux et produits maraîchers des sites d’agriculture urbaine de la région de Dakar (Sénégal) et représentation de leurs caractéristiques par les SIG.

Abstract
Urban agriculture occurs in most developing countries and contributes ore and more to food security and poverty alleviation, but also to public health and sustainable resource management. It produces cheaper and more diverse food, more green space in cities, improves sanitation by reusing wastewaters and creates additional income for households.
However, urban agriculture can have both positive and negative impacts on public health and environment:

General characteristics of urban agriculture are well documented, but scientific investigation of the relationship between urban agriculture and environmental sanitation is lacking (Baumgartner and Belevi, 2001).

This study is intended to fill this gap of knowledge by investigating heavy metals in waters, soils and crops. The objective is to be able to evaluate the actual risk of human exposure and to know which kind of soil is more appropriate for the retention of the toxic substances, for a safe agriculture. The degree of pollution, the influence of soil type, the dynamic of contaminant accumulation will be assessed. The negative impacts of wastewater reuse on crop, soils and ground waters will be quantified, as well as fluxes of contaminants. The effect of different water and nutrient sources (compost, faecal sludge) will be appreciated in order to define guideline values for wastewater reuse, depending of local soil types and irrigation practices. Localisation and prediction (modelisation) of pollution and risk exposure of urban agriculture in Dakar will be done by use of GIS. The GIS have a big potential for land and environment management in developing countries and this application will be a useful tool for local partners, NGO’s or municipalities in the actual theme of urban agriculture. Microbiological and epidemiological data (from IFAN and the diploma thesis that will done at the same time than the Ph.D.-project), will be considered together with heavy metals.

Samples of soils, percolation waters, ground waters and vegetables will be taken on several agricultural sites thank to the implementation of piezometers and lysimeters, as well as wastewaters. Solid phase analysis by XRF will be performed at University of Lausanne and water analysis will be performed both in Lausanne and Dakar by ICP-MS and Polarography-Voltametry. This way, the reliability of local measures will be evaluated.

This study will create a new partnership between Centre d’Analyse Minérale (Faculté de Geosciences et Environnement, Université de Lausanne) which has 20 years of experience in studying contaminated sites and is fully equipped, Laboratoire de traitement des eaux usées (IFAN, Univ. C.A..Diop, Dakar) which is specialised in urban agriculture and is developing a performing laboratory for wastewaters analysis and IRD (Institut français de recherche et Développement, Dakar) which works on anthropogenic soils. The Swiss institute of SANDEC, which supervises scientific research on urban agriculture and sanitation in developing countries will also contribute to this study. The local partners, who have poor experience in heavy metals analysis and in GIS, will be able to test the validity of their laboratory and acquire new competence in GIS for the next part of the project. This can create a pole of competence for them at a national level.



Personnes ressources au Nord :

Faculté des GéoSciences et de l’Environnement (Université de Lausanne):
Hans-Rudolf Pfeifer (directeur de thèse)
Centre d’Analyse Minérale
BFSH2
1015 Lausanne
hans-rudolf.pfeifer@cam.unil.ch

Personnes ressources au Sud :

Institut Fondamental d’Afrique Noire (Université Dakar) :
Seydou NIANG (codirecteur de thèse)
Laboratoire de traitement des eaux usées
I F A N, Université C.A.Diop
Boite Postale 206
DAKAR, Sénégal
seyniang@refer.sn

Institut français de Recherche et Développement :
Dr Guisse, responsable du projet sur les sols anthropiques
Rte de Hann
DAKAR, Sénégal
alguisse@refer.sn