The samples used in this study are of several types:

- animals and plants: fish (Oreochromis niloticus); market garden products (Solanum lycopersicum);

- sediments: water; sediments and soils.

These samples were taken at Houin Logbo on the banks and on Lake Toho. Figure 1 provides information on the geographical location of the lake.

Figure 2 and Figure 3 show the results of microbilogical contamination.

Analysis of these figures revealed the presence of Escherichia coli and fecal enterococci in all samples. The presence of thermotolerant coliforms including Escherichia Coli shows that the contamination is either recent or continuous because the Escherichia Coli germ does not last in the environment. The highest value obtained for Escherichia coli is 1200 CFU/100 mL. The results hereby differ from those obtained at Lake Nokoué, the values of which vary between 4000 CFU/100 mL and 6000 CFU/100 mL [4]. Indeed, we could have had a high dose of Escherichia Coli and faecal enterococci in Houin Logbo since the environment is humid, and very favorable to the multiplication of these bacteria. However, after observation in the field, we observed that market gardeners and farmers use herbicides such as glyphosate, a very effective vectorial but classified since March 20, 2015 as “probably carcinogenic” by the International Agency for Research on Cancer (IARC), an agency of the WHO. These elements, hostile to life, could also act on the bacteriological density.

Tables 1-5 show the results obtained after determinations of metal trace elements (MTE) in water, sediments and soils.

From these tables, it appears that the water of Lake Toho in Houin Logbo is polluted by lead, cadmium respectively 258 times and 219 times higher than GESAMP standards. As for the fish species Oreochromisniloticus, the most consumed by the natives, it has accumulated cadmium and arsenic in its flesh, respectively 1.4 and 1.7 times higher than WHO standards. The MTE determined by the present study were not found at ground level, but market garden products (Solanumlycopersicum) are contaminated by lead and cadmium. The consumption of the fish species Oreochromisniloticus and Solanumlycopersicum market garden products by the population constitute a real health risk for them. The average levels of lead (0.1032 mg/kg), cadmium (0.04673 mg/kg) in water are different from those obtained by Hounkpatin et al., [9] (Pb: 0.56 mg/L; Cd: 0.03 mg/L) and Montcho et al., [14] (Pb: 0.12 mg/kg; Cd: 0.03 mg/kg); As: 7.36 mg/kg); respectively in the lakeside city of Ganvié and in the Ouémé river. The average lead contents (14.79 mg/kg) are lower than that obtained by Hounkpatin et al. [15] (Pb: 54.04 mg/kg) in the lakeside town of Ganvié but higher than those of Dimon and al., [16] (Pb: 0.12 mg/kg) at Lake Ahémé. As for the concentrations of arsenic (0.800 mg/kg) and cadmium (1.27 mg/kg) in the sediments obtained by the present study differ from those obtained by Hounkpatin et al., [15] (Cd: 0.74 mg/kg) in the lakeside city of Ganvié but also those of Dimon et al. [16] (Pb: 0.12 mg/kg; As: 29 mg/kg) in Lake Ahémé. The average levels of lead, cadmium and arsenic in the sediments of Lake Toho in Houin (Pb: 14.79 mg/kg; Cd: 1.27 mg/kg; As: 0.800 mg/kg) are higher than the average levels lead, cadmium and arsenic from water (Pb: 0.1032 mg/L; Cd: 0.04673 mg/L; As: 0 mg/L) from the same lake. This could be explained by the fact that these metals are absorbed on the particles of the sediments, are then released by the mixing of the sediments and dissolve in the aqueous medium [15]. The levels obtained in fish (Oreochromisniloticus) at Houin Logbo (Pb: 0.143 mg/kg; Cd: 0.87 mg/kg; As: 0.466 mg/kg) are higher than those in water (Pb: 0.1032 mg/L; Cd: 0.04673 mg/L; As: 0.0025 mg/L) from the same lake. This would indicate the phenomenon of bioaccumulation. Because soils have the property of fixing MTE, in particular in surface horizons rich in organic matter [17]. Regarding market garden products, the values obtained are all lower than those found at soil level (Pb: 8.528 mg/kg; Cd: 2.755 mg/kg; As: 0.93 mg/kg). Indeed, plants can absorb MTE from the soil through their roots, transport them through the xylem and accumulate them in the various tissues of all organs (root, stems, leaves) [17]. This can lead to direct risks to human health through food plants or indirectly due to accumulation in the food chain through fodder.

Figure 4 and Figure 5 present the Danger Quotients (DQ) linked to the consumption of fish (Oreochromis niloticus) and market garden products (Solanum lycopersicum).

Analysis of the figures shows that the hazard quotients (DQ) obtained in children are all higher than those in adults, whether it is fish (Oreochromis niloticus) or market garden produce (Solanum lycopersicum). This is why children are always the most exposed to metallic trace elements due to their low body weight and their physiological fragility since contaminants are easily absorbed by their bodies [18]. Children’s bodies potentially absorb more contaminants and remain unable to eliminate them than those of adults because their elimination systems are less developed [15]. The hazard quotients for lead through the consumption of fish and market garden products (Solanum lycopersicum) are less than 1 in both children and adults. This confirms that the fish species Oreochromis niloticus from Lake Toho in Houin

Logbo and Solanum lycopersicum market garden products are not contaminated by lead.

The consumption of fish, in particular the Oreochromis niloticus species from Lake Toho in Houin Logbo, exposes the population to the risk of cadmium and arsenic poisoning, while the consumption of market garden products, in particular Solanum lycopersicum, exposes the population to risks cadmium poisoning.