Pesticide Residue Levels in Water and Sediment from River Thiba, Kirinyaga County, Kenya

The study assessed the physicochemical parameters and pesticides residue levels in water and sediment samples from Thiba River Catchment area, Mwea Irrigation Scheme, Kirinyaga County, Kenya. The samples were collected from six selected sampling sites in February and May 2021 representing dry and wet seasons respectively, by the meteorological department and based on the human activities and crops grown. The physicochemical parameters determined were pH, total dissolved solids (TDS), total suspended solids (TSS) and electrical conductivity (EC) in water samples and pH and total organic carbon content in the sediment samples. The pH of water samples ranged from 6.12 ± 0.12- 6.91± 0.17, as Total dissolved solids were at 10.03 ± 2.04 mg/L – 100.04 ± 1.10 mg/L while Total Suspendeed Solid values were 103.01 ±3.51mg/L -316.01 ± 6.81 mg/L, and Eelectrical Conductivity was in the range of 30.01± 1.21 µscm-1–200.13 ± 2.01 µscm-1. In the sediment samples, the pH ranged from 5.42 ± 0.12 – 7.52 ± 0.11 and the organic matter content ranged from 27.72± 0.62 – 49.07± 0.78. The farmers applied 12 different pesticides, under different trade names and active ingredient. Chlorpyrifos was the highest used pesticide by 72 % of the farmers followed by Lambda-cyhalothrin at 64 %. The pesticides obtained from the samples were Metalaxyl, chlorpyrifos, and lambda cyhalothrin. In the water samples, chlorpyrifos residue levels ranged from 3.60±0.92 µg/L – 88.24 ±65.97 µg/L, with Metalaxyl from