The fish farm concerned by this study is located in Zépréguhé, in the communal territory of Daloa, 9 km far from the city on the road to Bouaflé (Figure 1). This farm is a supply source for Daloa. Where the demand is so high due to the population growth. In fact, Daloa is the third big city in the country with estimated population of 245,360 persons in 2014 an area of 9650.75 ha.

This study is about the analysis of water taken from fish farming ponds in diversion connected to a river. Figure 2 shows the area of ponds in diversion among the fifteen (15) that the farm visited.

The chromatographic analysis made on the samples of fish farming of ZEPREGUHE revealed the presence of nine (9) pesticide residues. These are α-HCH (lindane), heptachlor, aldrin, β-endosulfan, PP-DDD, endosulfan-sulfate, α-endosulfan, cypermethrin and methoxychlor. They are all from the organochlorin family except the cypermethrin which is a pyrethroid (Table 1). Most of these pesticides detected are insecticides that are used in the spraying of coffee and cocoa farms close to fish farmings. And the presence of these substances pond water could be explained on the one hand by the action of the wind that may have directed the pesticide particles contained in the insecticides directly into the ponds during spraying [10]; and, on the other hand, by the action of rainwater that washes up the substances applied to the plantations into the water bodies of the river which supplies the fish farm. Among the pesticides detected, some are forbiden because of their toxicity and ecotoxicology. Their presence in the water shows the fraudulent use of their formulations containing these substances. Traoré and collabotaters have also noted this fraudulent use of organochlorins (endosulfan, lindan, heptachlor) in coffee and cocoa production areas [11]. That is so frightening because some studies classify most of the organochlorins among the endocrinious subversives and the carcinogen molecules [12] [13].

LOQ = 0.018 µg/L.

The residues have been detected in more than 50% of the samples analysed with some concentrations superior to, in most cases the quantification limit (LOQ).

Among the nave (9) pesticide residues detected, five (5) are found in all the waters of all the ponds. These are: lindan (α-HCB), β-endosulfan, PP-DDD, α-endosulfan and methoxychlor. Moreover, among these compounds, α-endosulfan is the molecule with the highest average concentration, with 0.8038 µg/L detected in Pond 2. This value is higher than the maximum permissible concentration of 0.1 µg/L of alpha or beta endosulfan in surface water defined byWorld Health Organization [14] or European Directive 2008/105/EC for 41 substances or groups of substances. The risk of indirect contamination of populations is therefore real since it has been shown that endosulfan is not only a very persistent molecule in the environment but also has a high capacity to bioaccumulate in aquatic organisms, particularly fish, with bioconcentration factor values sometimes ranging between 2400 and 11,000 for whole fish [15].

Table 2 shows the level of contamination per pond by doing the sum of concentrations of the residues detected in the water matrix. Comparing total concentrations from each pond, the following order is obtained: [Pond 3] < [Pond 4] < [Pond1] < [Pond 5] < [Pond 2]. The concentration of pesticide residues in the different ponds could be linked to the acreage and depth of ponds.

The dosage of pond water by the spectroscopy of atomic absorption (SAA) has shown that this water contains trace metal elements sought after which are lead, cadmium, mercury and arsenic. The average concentrations of these TMEs are spread in Table 3.

The results indicate that the pond waters studied have all the same contamination level to the trace metal elements, because statistical analysis has shown that, there is no striking difference between the samples for the different concentrations of TMEs (statistically identical with P > 0.05). In fact, all the ponds are close to rubber, coffee and cocoa farms, that are maybe sources of contamination in TME with the use of fertilisers and agrochemicals [16] [17].

These fish farmings are vessel of wastewater from the keeping up of these farms upstream. Also, runoff water could carry in its passage hydrocarbons and other waste from garages, landfills and households, and loaded with trace elements to flow into the river that feeds these ponds. In terms of global concentrations, when the cumulative concentrations of detected TMEs are calculated per pond, Table 3 also shows that the pond (pond5) has the highest level of TME contamination. The explanation for this lies in the location of the different ponds in relation to the potential sources of contamination. Indeed, among the five (5) ponds studied, pond (E5) is the one closest to the road that adds to the

n: number of samples; P: ponds.

other sources of pollution that the whole fish farm is confronted with. And this position makes it (pond E5) more vulnerable to pollution from car traffic, especially through vehicle exhaust fumes which contain traces of metals alongside. According to some authors [18], fuels contain mercury (Hg), cadmium (Cd), copper (Cu) and lead (Pb) in their composition, although the presence of this last element in the composition of fuel is increasingly questioned in recent years.

Comparing these average contents with the standards in use, it appears clearly through Figure 3 that except lead, the average concentrations of TMEs in the pond water are all superior to threshold values [19]. The content in arsenic (As) is about four times superior to norm. In fact, the histogram (Figure 3), reveals that the average concentration in lead (1.6142 μg/L), remains low compared to the requirements fixed to 10 μg/L. This result conforms to that Diop and collaborators [20], obtained in Dakar in 2014 that evaluating the contamination and the speciation of trace metals in a river containing fish alife, obtained that the average lead (Pb) oscillated between 0.047 and 3.87 µg/L. This result shows that the samples taken would not present any risk of infection or lead contamination in relation to the standard set. On the other hand, the levels of mercury (0.529 μg/L), cadmium (0.847 μg/L) and arsenic (9.174 μg/L) obtained are respectively higher than the reference values set (0.1 μg/L; 0.2 μg/L; 2 μg/L). These results are worrying insofar as cadmium poisoning could cause cancer effects in exposed individuals and lead to endocrine and/or immune system dysfunction in children [21]. Mercury and arsenic are also known to be acutely toxic at low doses, causing infections of the cardiovascular system and other serious illnesses in humans who are exposed indirectly through the consumption of fish in which these contaminants accumulate [22] [23].

Figure 4 presents through the cloud of points the concentration levels of the metallic trace elements studied (Pb, Hg, Cd, As) in each of the fifteen (15) samples. The decreasing order of average concentration of the molecules studied are as follows: [As] > [Pb] > [Cd] > [Hg]. Arsenic is the composite that presents the highest contents with a maximum concentration reaching 9.497 µg/L. Anyway, there is agreat difference between the concentration level of arsenic and that of the three (3) other metals studied, as shown in Figure 4. This preponderance of arsenic in the water could be due not only to the regular use of fertilisers, herbicides or insecticides in the surrounding plantations, but also to the dust heaps or leaching and drainage water from the sand extraction activity carried out near the ponds. Arsenic accumulates naturally in magmatic and sedimentary rocks [24], and sand is usually produced by the weathering and erosion of rocks.