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The Dakar region is a mega city with multiple contaminant sources from urban expansion as well as industrial and agricultural activities. The major part of the region is underlain by unconfined sandy aquifer, which is vulnerable to contaminants derived from human land use. At present, the contaminated groundwater which extends over a large area in the suburban zone of Thiaroye poses a threat to the future of this valuable resource, and more specifically, a health threat. This study focuses on nitrate pollution occurrences and associated processes using nitrate isotope data (15NNO3, 18ONO3) combined with environmental isotopic tracers (18O, 2H, and 3H). Samples from 36 wells were collected to determine the level, distribution, and sources of contamination in relation to land use. Results indicate that shallow groundwater in the urbanized area of Thiaroye shows distinct evidence of surface contamination with nitrate as much as 300 mg/l NO3-. In rural area not serviced by water supply distribution network, much higher NO3- contents were found in few wells due to household and livestock feedlots. In most groundwater samples d15N values ranged from + 10 to + 22 parts per thousand, indicative of predominantly human and animal wastes. This was confirmed by environmental isotope data which suggest a mixture of polluted recharge waters. By using the dual d15N vs d18O as well as d15N vs NO3- approach, denitrification may occur to some extent but it is blurred by mixing with new infiltrated nitrates and cycling derived from continuous leaky septic system. Results suggest that nitrate contamination of the aquifer is a consequence of unregulated urbanisation (homemade latrines), continuing contaminant transfer in shallow water depth where aerobic conditions prevai

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Communications ExperimentalThe synthesis and purification of bis(dimethylglyoximato)platinum(II) (Pt(dmg) 2 ) has been reported elsewhere [12]. The metal complex was deposited on a cleaved KBr(001) substrate under 4´10 ±7 mbar of residual gas using an organic molecular beam deposition apparatus [29]. The thickness of the evaporated films was controlled by regulating the distance between the substrates and the Knudsen cell in which the metal complex was held. The evaporation temperature was ca. 200 C, and the substrate was kept at room temperature during deposition. The topographic images from atomic force microscopy (AFM) of the evaporated films were measured in air by a Seiko SP-3700 in contact mode. The transmission electron diffraction was taken by a Zeiss CEM-902 with an accelerating voltage of 80 kV. The observed film was stripped from the KBr substrate by immersion in water after being reinforced with an amorphous carbon coating. XRD measurements of the evaporated film on a KBr substrate were performed on a Mac Science MXP-18 diffractometer with Cu Ka radiation source (1.5405 ). Reflections were recorded over a 2y range from 6 to 60.