Pesticide Residue Levels in Soil, Water, Kales and Tomatoes in Ewaso Narok Wetland, Laikipia, County, Kenya

Abstract

Soil, water, kales and tomatoes from Ewaso Narok wetland were collected during wet and dry seasons and analyzed for 15 pesticide residues. Multi-residues method (QuEChERS EN) was used for sample preparation and Liquid chromatography-tandem mass spectrometry (LC-MS/MS) used for analysis. The soil was highly contaminated compared to water, kales and tomatoes. Banned (Aldicarb, azinphos methyl) and restricted (diazinon, chlorpyrifos and fenpropathrin) pesticide residues were detected in sample matrices in different concentrations. Residues levels that exceeded the European Union (EU) maximum residues limit (MRLs) were found in kales (triadimefon, cyproconazole I and II, fenpropathrin), tomatoes (cyproconazole I and II, fenpropathrin and spiroxamine) and water (aldicarb). All the pesticide residues concentrations were within the recommended levels of the World Health Organization (WHO) and Agricultural Food Organization (FAO). Residue levels were significantly high in the upstream and midstream during wet and dry seasons. Temperatures, conductivity (EC), pH, salinity, total dissolved solids (TDS) and dissolved oxygen (DO) were measured to assess soil/water quality. All the physicochemical parameters were within the recommended levels. Though most residue levels were below the EU-MRLs, MCLs and within the toxicological levels (LD50), the negative effects of the long term exposure to the wetland biodiversity and human health are real and should not be ignored. Farmers need to embrace Good Agricultural Practices (GAP) in order to reduce over-reliance on pesticide use in the wetland.