Physicochemical Quality of Water Resources in the Téguéré River Watershed in the Face of Pressures from Periurban Market Gardening in Korhogo, Northern Côte d'Ivoire

Abstract

In Korhogo, the Téguéré River watershed is home to intensive peri-urban market gardening. The widespread use of pesticides poses a significant risk to water resource quality. This study aims to assess the impact of pesticides on the quality of water resources in the Téguéré watershed. To this end, ten water points were sampled, including four surface water sources (river) and six groundwater sources (wells). Physicochemical parameters and pesticide concentrations were measured. Pesticide contamination indices (PCI) and pesticide alteration indices (PAI) were calculated. Principal component analysis (PCA) identified measurement points groups. The results reveal that the average temperatures of surface water (31.9°C) and groundwater (31.03°C) are higher than the WHO recommended standard (25°C). These waters are acidic, with an average pH of 4.264. Conductivity is higher in surface water (230 µS/cm) than in groundwater (75 µS/cm). Analysis of pesticide residues identified sixteen (16) active molecules belonging to six (6) chemical families: organophosphates, organochlorines, triazines and their metabolites, carbamates, substituted ureas, and pyrethroids. The majority of molecules detected in these waters have concentrations above the WHO guideline value (0.1 µg/L), with a maximum concentration of 3.45 µg/L for chlorpyrifos-ethyl recorded at sampling point No. 4. Triazines and their metabolites dominate surface waters, while organophosphates are most abundant in groundwater. Contamination index (PCI) results indicate that 20.1% of surface waters are of good quality, 47.9% are of poor quality, and 32% are of very poor quality. As for groundwater, 60.86% of samples are classified as good quality and 39.14% as poor quality. The PAI reveals an average value of 5.30 µg/L for surface water, indicating very poor quality, and 1.9445 µg/L for groundwater, indicating degraded quality. The discrimination of pesticide sources by PCA, reveals three distinct poles: intensive agriculture, hydrological interactions, and watersheds with their own characteristics.