Water, a vital resource for all living beings, is a fundamental need of Man and is involved in domestic, hygiene and food use [1]. When it is taken as a drink, water must be potable. It must therefore meet the quality requirements set by the relevant standards concerning microbiological, chemical, radiological and aesthetic aspects [1]. Whether it is surface water (river, stream, lake or pond water) or groundwater (well, borehole, tap water), its quality is a determining factor for health [2]. Water quality is strongly influenced by anthropogenic pressures such as urbanization, industrialization, agriculture, port activities and shortcomings in sanitation. These human activities would therefore contribute to a deterioration of water quality through the production of pollutants that may end up in water [3]. Among these activities are those linked to ports and to mining. In Togo, previous work has highlighted the link between mining activities and cases of water pollution by heavy metals [4]. As regards port activities, they can lead to water pollution [5] through the accidental or deliberate discharge of hydrocarbons and waste by ships, and through run-off water which carries organic waste, heavy metals and particles towards water sources. In the port zone of Lomé, also classified as a free zone, the high concentration of industrial activities increases the risks of pollution. Indeed, this port free zone is heavily industrialized with nearly 36 industries, operating in the cosmetics, chemical, plastics, food, metal and pharmaceutical sectors [6]. These industries could also generate pollutants. In addition to these toxic substances, the presence of pathogenic microorganisms or bacteria can also alter water quality, thus contributing to water pollution [7]. Water pollution corresponds to its degradation or contamination through the introduction of toxic substances. These substances would affect the natural characteristics of water, in particular the biological and physicochemical characteristics, thus constituting a health risk in the event of consumption by the population. In 2019, water pollution was the cause of 1 - 4 million premature deaths throughout the world [8]. In Togo, previous studies carried out in certain localities of the country, in particular in Lomé [7], Tsévié [9], Tchaoudjo [10] and in the mining area of Bangéli [4] have made it possible to assess water quality in these areas. However, despite the high population density and the industrial concentration in the port zone of Lomé [8], no scientific data exist on the impact of port activities on the quality of the environment. This work therefore falls within the framework of the physicochemical and microbiological characterization of pollution in an industrial and urban setting with a view to assessing the water quality in the port zone of Lomé.

The results were presented by type of water (well water, borehole water and wastewater) and by group of parameters (physicochemical and microbiological parameters), as well as the bioassays.

Water quality is influenced by various factors, in particular anthropogenic activities [14], and can be assessed through physicochemical and microbiological parameters. Among these parameters, mention may be made of physicochemical parameters such as turbidity, temperature, conductivity, pH, the concentration of mineral elements (ammonium ion, calcium, magnesium, chloride, sodium, nitrates) [10] or organoleptic characteristics such as taste and odour [1].

Turbidity is a parameter that makes it possible to measure the cloudiness of water. It is due to suspended particles such as sediments, organic matter and microorganisms [15]. A high turbidity reflects potential pollution, the suspended particles being able to constitute vectors of heavy metals and microorganisms. The results of this study on the groundwater samples (well water, borehole water) made it possible to record a turbidity below the limits recommended by the WHO (≤5 NTU) [15]. This result is similar to that of Ouéda et al. [10] who detected a turbidity complying with the WHO standards in the water samples of the Didaourè agglomeration (Tchaoudjo 1). In contrast, our results differ from those of Tampo et al. [16], who recorded a turbidity above the standard in well water during their work in Démakpoé and Agbalépédogan (Lomé) [16]. In contrast, in the surface water (wastewater 3 and 4), turbidity was high, indicating possible pollution of these waters. The high turbidity observed in these samples would therefore be linked to the presence of insoluble solid particles in suspension. This result as regards wastewater is similar to those of Ayah et al. [3] who recorded a high turbidity (35 NTU) during a study on the lagoon system of Lomé [3].

The SS values of these two samples were also high, far exceeding the regulatory value set by interministerial order MER/MS/MERF No. 010 of 30 March 2015 (≤50 mg/L) [17]. This result is also similar to those of Ayah et al. [3] who indicated an SS of 77 mg/L in the lagoon system of Lomé [3].

According to the WHO, water temperature should not exceed 25˚C. In this study, some well waters and one wastewater sample exceeded this limit, which could favour microbial proliferation. Indeed, a high water temperature would favour the proliferation of bacteria [18]. This result is similar to those of Ouéda et al. [10] who, during their work in the Tchaoudjo 1 area, recorded an average water temperature of 26.17˚C, therefore above the WHO standard. Likewise, the work of Fambi et al. [19] in Togo, like that of Dégbey et al. [20] in Benin, also recorded temperatures above the WHO standards.

As regards pH, a physicochemical parameter which provides information on the acidity or the basicity of an aqueous solution, drinking water, according to the WHO, has an optimum pH between 6.5 - 9.5 [21][22]. The various well water and borehole water samples had a pH complying with the WHO standards. Our results are similar to those of Ouéda et al. [10] who during their work recorded pH values complying with the WHO standards. However, our results differ from those of Fambi et al. [19] who noted, during a study in 2021 on the borehole water of Légbassito and Vakpossito, two localities in the south of Togo, that 70 % of the waters had an acidic pH. These pH values were between 4.94 and 5.9 [19]. As regards wastewater, one sample had a pH not complying with the standard defined by interministerial order MER/MS/MERF No. 010 of 30 March 2015. Indeed, according to this order, the pH of wastewater should lie between 5.5 - 9 [17]. Wastewater sample 4 (WW4), which shows an acidic pH (4.35), and wastewater sample 2 (WW2) do not comply with the national regulations on wastewater. Thus, apart from wastewater sample 4 and, to a lesser extent, wastewater sample 2, the results of our study are similar to those obtained in Morocco by Boutayeb et al. [23], who recorded pH values between 7.05 and 8.2 for various wastewater samples.

Conductivity, which reflects the mineralization of water, expresses its capacity to carry the electric current. It was high both in the groundwater (well and borehole water) and in the surface water (wastewater and water of the 4^th lake). This result is different from that of Gnazou et al. [24] who obtained a conductivity ranging from 70.5 µS/cm to 1756 µS/cm. In contrast, our result is similar to that of Talhaoui et al. [25] who recorded conductivities, with a maximum of 2240 µS/cm during their work in Morocco. According to the European Union (EU) standards, conductivity should be less than or equal to 2500 µS/cm, but permissible value is 400 µS/cm for drinking water. A high conductivity would indicate natural pollution (erosion of rocks) or anthropogenic pollution (agriculture, industries or domestic discharges) [15].

Our study also revealed, in some well water samples (W1, W2 and W4), borehole water samples (BH1) and wastewater samples (WW3), the presence of nitrogen compounds such as nitrates at concentrations above the EU and WHO standards. As regards well water, our results are similar to those of Gnazou et al. [24] who had also recorded high nitrate concentrations in well water in the Zio area. Likewise, the work of Ouéda et al. [10], indicated that 66.67% of the water samples studied in the Didaourè agglomeration had a nitrate concentration above the WHO standards. Ahoudi et al. [22] during their work in the Agoè Zongo area, also recorded high nitrate contents in the various water samples. High nitrate concentrations reflect contamination linked to the leaching of agricultural soils or to urban and industrial discharges.

The ammonium ion, another nitrogen compound, was present at a high concentration in borehole sample 1 (BH1). This result associated to nitrite and nitrate high level in BHI, indicate a possible punctual source of contamination, mainly a possible domestic contamination (human discharges) [10]. This result is similar to that of Ouéda et al. [10], who recorded a high level of ammonium ion in one of their water samples.

The COD of some wastewater samples (WW2, WW4) was high compared with the standard set by interministerial order MER/MS/MERF No. 010 of 30 March 2015 [17]. These results reveal a heavy contamination by refractory pollutants of organic and mineral origin [23]. Indeed, the chemical oxygen demand provides information on possible organic pollution of water [26]. Our results are similar to those of Sema et al. [27] who, during their work in Kara, also recorded high COD values. However, these COD values were high only in the mornings, owing to the discharge of wastewater by the industries [27].

As for the biochemical oxygen demand over 5 days (BOD₅), its value in the wastewater samples (WW2 and WW4) did not comply with the standards in force in Togo. Moreover, the biodegradability index of the wastewater (WW1-WW4) was above 3, thus confirming the presence of non-biodegradable refractory pollutants [28]. Indeed, the biodegradability index makes it possible to assess the biodegradability of organic matter [28] while giving indications on the origin of the pollution [29].

Finally, as regards the concentrations of trace metal elements, the contents found in well water and borehole water were generally in compliance with the WHO Guidelines in 2006. In contrast, in some wastewater samples, the content of trace metal elements such as As did not comply with the Togolese regulations in this field. These results are similar to those of Kpiagou et al. [30] who had also detected high levels of As in the water resources of the Didagou catchment. These results underline the need for an appropriate treatment of wastewater. Indeed, trace metal elements are non-biodegradable toxic pollutants which accumulate in the environment with negative impacts on health [31].

Most of the wastewater also had an odour, testifying to the alteration of the organoleptic characteristics.

Biological assessment, in particular microbiological analysis, constitutes another component of the study of water quality.

In the groundwater and surface water samples, the presence of heterotrophic bacteria at values clearly above the WHO guidelines would indicate a contamination of the water following exposure to overall pollution.

Thermotolerant coliforms (TC) were also found in the groundwater samples at abnormal values, indicating suspected faecal contamination [7]. The heterotrophic plate count and TC values in well water are clearly higher than those found in borehole water (except those of BH2). This difference would be linked to the fact that boreholes are generally deeper and less exposed than wells [11]. The results obtained in this study as regards HPC bacteria and TC in well water and borehole water are similar to those of previous work carried out in Adakpamé [11] and Lomé [7]. This work indeed also recorded the presence of HPC bacteria and faecal coliforms in well water and borehole water. As regards wastewater, only one sample showed TC and enterococci values below the national standards.

Salmonella and clostridia were also found in most of the wastewater. These pathogenic bacteria are indeed often found in wastewater [32].

Just like the physicochemical and microbiological analyses, bioassays also make it possible to assess water pollution [13]. The bioassay with the larvae of Artemia salina indeed makes it possible to obtain indications on possible toxicity and on the ecological quality of the water. The high mortality rates observed in the majority of the wastewater and in one well sample can reveal probable toxicity.

The larvae of A salinatherefore made it possible to obtain indications on the toxicity of the various water samples of the port zone, by serving as bioassay material.

The physicochemical analysis highlighted several anomalies, particularly in the wastewater. From the microbiological point of view, the well water, borehole water and wastewater were contaminated by heterotrophic bacteria and by pathogenic germs. To this is added the high mortality observed during the bioassay on the larvae of Artemia salina, particularly in the wastewater. These results reflect a probable pollution of the waters in the port zone of Lomé. Further researches must be conducted to determine rather contaminations are due to Lomé’s port activities or not.