DETERMINATION OF LEVELS OF HERBICIDE RESIDUES AND PHYSICOCHEMICAL CHARACTERIZATION OF SEDIMENTS FROM SELECTED RIVERS IN AGRICULTURAL AREAS OF TARABA STATE, NIGERIA

Abstract

This study investigated the presence of glyphosate, 2,4-dichlorophenoxyacetic acid (2,4-D), their degradation products and associated physicochemical properties of river sediments from three agriculturally impacted rivers- Kpantinapo, Bakin-Dutse and Lamurde/Nukkai- in Taraba state, Nigeria. Twelve sediment samples were analyzed for pH, total organic carbon (TOC), total organic matter (TOM), cation exchange capacity (CEC) and particle size distribution using standard procedures (Walkley-Black, ammonium acetate and hydrometer methods, respectively). Herbicide residues were extracted via soxhlet extraction with n-hexane and acetone, cleaned, derivatized and quantified using Gas Chromatography-Mass spectrophotometer (GC-MS). 2,4-D was not detected in any of the samples, likely due to its rapid degradation; however, the degradation product 2,4-dichlorophenol was found at a mean concentration of 1.12 mg/kg in six sites. Glyphosate was detected more frequently with a mean concentration of 1.22 mg/kg, indicating more extensive use. Residue concentrations were generally higher in intertidal zones compared to bottom sediments, likely due to surface run-off from surrounding farmlands. Sediment pH ranged from acidic to neutral and moderate levels of TOC and TOM support a medium capacity for contaminant retention and mobility. These findings highlight the persistence of certain herbicide residues and underscore the need for continuous sediment quality monitoring to inform sustainable agricultural and environmental management practices in the region.