The objective of this study was to evaluate the typology of water through physicochemical and bacteriological characterization with the aim of highlighting its vulnerability as a drinking water resource. The methodology adopted was to evaluate the level of pollution by monitoring the spatiotemporal variation of the water pollution indicator levels of Lake Dohou. The sampling frequency is monthly for one year, from November 2017 to October 2018, in order to obtain a fairly representative image of water quality and its seasonal evolution in eight (8) well-defined stations. The parameters were determined using the standard methods defined by the French Association for Standardization (AFNOR). This study shows that the waters are acidic, with an average pH of 5.81 and a low electrical conductivity of between 42.67 ± 4.30 and 59.62 ± 21.84 μS•cm −1. At all stations, seasonal mean water transparencies are low (<1 m). It is also noted that 99.7% of the water samples collected had total nitrogen (TN) levels above the limit of 4 mg•L −1. All of the lake's waters have non-compliant BOD5 (<3 mgO 2 •L −1) for raw water intended for the production of drinking water. Sites D6 and D7 have COD/BOD5 ratio greater than 3, which indicates the presence of non-biodegradable organic matter in these areas. Total coliforms, Escherichia coli and Enterococci were present in 100% (28/28) water samples at concentrations ranging from 2300 to 173,000 CFU/100 mL, from 100 to 1650 CFU/100 mL and from 20 to 1140 CFU 1/100 mL respectively. For Salmonella pathogens, they were detected in 50% of the dry season samples and in 100% of the rainy season samples. This almost permanent presence of this pathogenic germ denotes a poor quality of water with reference to this parameter.

The purpose of this study was to evaluate the contamination by heavy metals and the health risks of the residents of a watershed of the Sassandra river. Water and fish samples were taken from Guessabo Lake during the dry season and the rainy season. The average Hg, Pb, Cd and Zn concentrations in the water samples decreased during the rainy season by 20.51%, 80%, 18, 26% and 61.4%, respectively. In contrast, the average concentrations of As, Cu, Mn and Fe increased by 10%, 84.3%, 48.98% and 11.45%, respectively. The concentrations of heavy metals in water samples follow the trend: Fe> Cu> Mn> Pb> As> Zn> Hg> Cd. All metals except Fe were within permitted limits for drinking water quality at all stations during both seasons. The increase of As, Mn and Fe in water samples during rainy season was inversely proportional to their covalent index. The average heavy metal pollution index (HPI) for each sampling station showed higher pollution at the G2 station. The average Heavy metal evaluation index (HEI) of dry season (28) decreased relatively after the rainy season (21). Pearson's analysis showed that cadmium correlates strongly with HPI (r = 0.896) and HEI (r = 0.95) and iron is also highly correlated with HPI (r = 0.961) and HEI (r = 0.999). The concentration of trace metals obtained in the muscles of Chrysichthys nigrodigitatus (demersal) and Tilapia spp (benthopelagic) showed that Tilapia spp concentrated more non-essential metals (Hg, Cd and As) than Chrysichthys nigrodigitatus. Human health risks of trace metals in fish muscle and water were low, but among the selected metals, As and Hg are the non-essential elements contributing more to the cumulative hazard quotient of HI (0.845) for children and (0.39) for adults.

The aims of the work were to study the current quality of the water in Lake DOHOU used for drinking water supply through several physical, chemical analyses and using water quality indices (WQI). In addition, the question was whether the populations are at risk after drinking water of lake following a reduction of 50% and 75% in the median and maximum values of pesticides. Thus, the results of the pesticide monitoring program were incorporated into probabilistic human health risk assessment exercises. Water samples were collected over a period of one year. Pesticides were subjected to solid phase extraction and then analyzed using gas chromatography coupled to tandem mass spectroscopy. The other parameters were measured according to conventional methods. The results showed that the most frequently detected pesticides were aldicarb (79%), simazine (79%) and monolinuron (44%). They also showed the mean values of concentrations exceeding 1.5 μg/L. Metoxuron detected at a frequency of 29% showed the maximum average concentration (13.46 μg/L). Nearly 98% of the sampling points had at least one substance with an average concentration above the quality standard (0.1 μg/L) and 80% did not meet the total concentration standards. Cumulative risk quotient estimates after 50% or 75% abatement for frequently identified pesticides were greater than unity when extreme values for adults and children were considered. To determine the suitability of water for aquatic life, drinking water consumption and drinking water production, the water quality index (WQI), the heavy metal pollution (HPI) and the heavy metal evaluation (HEI) were calculated. The poor quality of the water was mainly related to pesticides, organic matter and microbiological parameters. Most of the nutrients and metals studied were often below the standards of drinking water