Occurrence of Glyphosate in Groundwater and Surface Water Within Farming Communities in Central Tongu District, Ghana

Abstract

The study investigated the occurrence/presence of glyphosate residues in groundwater and surface water from selected farming (Pepper, Maize and Cassava) communities within the Central Tongu district of Ghana. The study also evaluated the potential health risk posed to children and adults through drinking of ground and surface water. This was achieved through: (i) assessment of the levels of glyphosate residues in groundwater (Boreholes) and surface water within farming communities of Central Tongu; (ii) appraisal of physical parameters of the waters, as well as assessment of their influence on the levels of glyphosate residues via Principal Component Analysis (PCA); (iii) investigation of the relationship between glyphosate levels and water resources within Central Tongu district using Hierarchical Cluster Analysis (HCA); and, (iv) estimation of the Human Health Risk associated with consumption of groundwater (Borehole) and surface water by inhabitants (children and adults). Glyphosate residue levels were determined by LC-MS/MS; after extraction of glyphosate residues from water using dichloromethane. pH, Temperature, Salinity, Conductivity and Total Dissolved Solids (TDS) were measured on-site using LaMotte PockeTester Multi-meter. The pH of the borehole samples ranged from slightly acidic (5.69) to near neutral (7.4); whiles the pH of the surface water samples ranged from near neutral (7.35) to weakly basic (8.0). Temperature of borehole samples was between 29.7 to 33.5 ℃. The temperature of the surface water samples was also between 30.5 ℃ and 31.8 ℃. Conductivity of surface water ranged from 1025 to 1175 μS/cm; with that for groundwater samples (Borehole) ranging from 1350 - 11320 μS/cm. Salinity ranged from 450 to 570 mg/L; and 640 and 6640 mg/L for surface water and groundwater (Borehole) respectively. TDS for surface water ranged from 670 to 850 mg/L; and 920 to 7780 mg/L for borehole samples. Levels of glyphosate residues (Groundwater: 2.57 - 9.21 μg/L; Surface water: 25.10 - 42.50 μg/L) obtained were below the 280 μg/L Recommended Guideline Value for Canada; and the USEPA Maximum Allowed Concentration of 700 μg/L. However, the levels of glyphosate residue obtained were higher than the recommended 0.1 μg/L glyphosate residue in drinking water by the European Union. pH was identified as the sole physicochemical parameter influencing glyphosate residues in the water resources (through Principal Component Analysis [PCA]). Glyphosate residues were high in slightly basic water samples; and low in slightly acidic water samples. Hierarchical Cluster Analysis (HCA) also established close association between levels of glyphosate and the type of Water resources. The levels of glyphosate in groundwater were relatively low compared to the high levels of glyphosate in surface water. Assessment of Non-carcinogenic Risk using Hazard Quotient (HQ) for acute and chronic exposures revealed some level of risk associated with the consumption of groundwater and surface water from the selected farming communities in the Central Tongu district. For acute exposure, the HQ for groundwater ranged from 0.18 to 0.65 for adults; 0.36 - 0.80 and 1.19 - 1.29 (for two communities; Bakpa Dzave and Kanikope) for children. For surface water, HQ ranged from 1.77 - 3.01 (Adults) and 3.51 - 5.95 (Children). For chronic exposure, the HQ for groundwater ranged from 0.05 - 0.19 (Adults) and 0.10 - 0.37 (Children); whiles the HQ for surface water ranged from 0.51 - 0.86 and 1.00 - 1.70 for adults and children respectively. Groundwater/borehole water did not pose any potential health risk to both adults and children from chronic exposure. Though surface water did not pose any potential health risk chronically to adults; children are at risk. For acute exposure, borehole water did not pose a potential health risk to both adults and children; notwithstanding, children in Bakpa-Dzave and Kanikope were at risk. Acute exposure to surface water poses a potential health risk to both adults and children.