Kissao Gnandi

Increased Bioavailability of Mercury in the Lagoons of Lomé, Togo: The Possible Role of Dredging

Surface sediments of the lagoons of Lomé, Togo, were analyzed for mercury, methylmercury, and trace elements. Concentrations were greater than typical for natural lagoon sediments, and with greater variability within the Eastern lagoon compared to the Western one. The Eastern lagoon is larger and has been dredged in the past, while the Western lagoon, which also receives major waste inputs, has not been dredged and shows less tidal flushing. Accordingly, one naturally believes that the Eastern lagoon is cleaner and probably safe to use due to its natural resources, including fishes to eat. Unexpectedly, we describe here that mercury methylation was greater in the Eastern lagoon, indicating increased bioavailability of mercury, as probably facilitated by past dredging that decreased solid-phase retention of inorganic mercury. Urbanization has historically been more developed in the southern part of the lagoons, which is still reflected in contamination levels of sediment despite dredging, probably because sources of contamination are still more important there today. Such urban contamination emphasizes the need to regulate waste discharges and possible airborne contamination in growing cities of developing countries, and implements environmental and public health monitoring, especially in relation to misbelieves systematically associated with the cleansing effect of dredging activity.

Bioaccumulation de certains éléments métalliques dans les produits maraîchers cultivés sur les sols urbains le long de l'autoroute Lomé- Aného, Sud Togo

Abstract Several metallic elements were analyzed by ICP—AES in 10 vegetable species cultivated in market—gardening agriculture in Lomé and its suburban, along the highway Lomé-Aného, Togo. The results showed a high accumulation of these metallic elements both in the vegetables and in the soils. Leaf vegetables accumulated higher concentration of these metallic elements than bulb or tuber vegetables. These metals could result from the air pollution due to the intense industrial activity and the high road traffic in this site and from chemical fertilizers and pesticides used by the market-gardeners. This survey stated that the metallic elements from air, could accumulate in the legumes by foliar absorption. Furthermore, this study especially pointed out that legumes cultivated in this area could be improper for human consumption.

Distribution of Fluoride in the Phosphorite Mining Area of Hahotoe–Kpogame (Togo)

Background Phosphorites in the mining area of Hahotoé-Kpogamé contain high levels of fluoride that can cause illness among people living close to the mining and processing sites. Objectives To assess the distribution of fluoride in the different areas around the phosphorite mining areas in Togo. Methods Analyses were performed by molecular absorption spectrometer (HACH DR3800) according to the procedure manual at the geochemical laboratory of the University of Lomé. The sodium 2 - (parasulfophenylazo) - 1,8 - dihydroxy - 3,6 - naphthalenedisulfonate (SPADNS) method was used to determine fluoride contents and the PhosVer® 3 with acid persulfate digestion method was used to measure phosphorus pentoxide (P2O5). GraphPad Prism version 3.0 software was used for the data processing. Results The surface water of the mining sites had a fluoride content ranging from 0.38 to 3.52 mg/l (average = 1.33 mg/l; n = 10, n is the number of samples). Groundwater in this area had a fluoride content between 0.15 mg/l and 1.39 mg/l (average = 0.58 mg/l, n = 15). In the groundwater in the villages around the phosphorite processing plant, the fluoride content ranged between 0.15 and 0.63 mg/l (average = 0.41 mg/l; n = 22). The fluoride content in the water of the phosphorite mining area was higher than in Gbodjomé (reference area). Meanwhile, assessment of the effluents discharged into the ocean had a fluoride content ranging from 12 to 20 mg/l. In dusts, the P2O5 and fluoride contents were 36.02% and 1.85%, respectively. Vegetables from the local market garden produce showed levels of fluoride up to 2.06%. The average contents of P2O5 and fluoride in one of the phosphorite profiles were 32.38% and 3.00%, respectively. A significant correlation was observed between P2O5 and fluoride. Conclusions The correlation between P2O5 and fluoride in phosphorites shows that phosphorite mining is the main source of fluoride pollution in this area.

Assessment of pesticide residues and trace element contamination in market gardens of Togo

All intensive agriculture, like periurban agriculture, uses massive inputs such as agrochemicals. This study aims to assess the environmental impacts of agrochemical use in periurban agriculture in Togo. It was based on the chemical analyses of soil, water and vegetable samples. These analyses were carried out by gas chromatography on extracts from soil, water and vegetable samples. In soil samples, the concentrations of pesticide residues are lower than 20 ig/kg of dry material. For water samples, contamination levels vary from 0.02 to 1.1 ig/L of dry material with the highest levels for metalaxyl M (1.1 ig/L) and for dimethoate (1 ig/L). In vegetables, the concentrations measured are between 0.01 and 0.1 mg/kg of dry material. All these concentrations are affected by a positive factor of the maximum limits of residues. These agrochemicals, coupled with periurban environmental management led to the high concentrations of trace elements. Lead and cadmium concentrations in water are 10 and 21 times respectively higher than the maximum concentration allowable for drinking water by the WHO. The study showed that inappropriate use of agrochemicals in Togolese periurban agriculture creates ecological disturbances that could affect produce quality. Key words : Togo, periurban agriculture, agrochemicals, pesticide residues, trace element.