Status of Agricultural Soil Contamination by Heavy Metals in Uasin Gishu County

Abstract

Heavy metals occur naturally in the environment but anthropogenic activities such as use of chemicals and inorganic fertilizers in farms has resulted in higher concentrations of these metals relative to their normal background values leading to environmental pollution. Soil plays a central role in food safety as it determines the possible composition of food and feed at the root of the food chain. Soil pollution by heavy metals has been on the increase with its main sources being application of agricultural chemicals, improper disposal of industrial wastes, among others. This study investigated different concentrations of the heavy metals in soils of farms during the two major crop seasons in Uasin Gishu County, Kenya. The presences of heavy metals (Lead, Copper, Cadmium, Cobalt and Zinc) were determined in the three agro-ecological zones in Uasin Gishu County. These agro-ecological zones include Lower highland (LH3), Upper midland (UH4) and Upper midland (UH2). Soil samples from randomly selected farmers in the study area at the depth of 0-10cm and 10-20 cm were obtained. A total of seventy two soil samples were collected and analyzed for presence of heavy metals using ICPE-900Shimadzu inductive coupled plasma. The results obtained indicated that concentrations of the heavy metals found in soils at the three agro-ecological zones during the dry and wet seasons varied significantly.The results obtained showed that the mean concentration of Pb, Cd, Co, Zn and Cu in UH2 ranged between 12.0 –15.5ppm, 2.8–4.7 ppm, 2.5–9.5 ppm, 2.3–4.0 ppm, 8.0–16.3 ppm respectively, while in LH3 the concentration range between 10.0 –18.6 ppm, 1.8–4.8 ppm, 2.3–10.0 ppm, 2.0–17.3 ppm, 7.9–17.3 ppm respectively and finally in UH4, the mean concentrations of the five metals ranged between 10.3 –13.0ppm, 1.7–4.3 ppm, 4.0–8.5 ppm, 2.0–2.5 ppm, 7.7–16.5 ppm respectively. The level of Cd concentrations was found to exceed the WHO standard of 3mg/l in the study area. All the heavy metals concentrations varied significantly (P< 0.05) during wet and dry season indicating their mobility in the soils. The presence of heavy metals above the natural levels in the study area is attributed to sources such intensive agricultural activities. The results of this study revealed that the three agricultural zones of LH3 (Lower highland), UH4 (Upper midland) and UH2 (Upper midland) contained variable levels of heavy metals (Pb, Cd Zn, Co and Cu). The levels of heavy metals were high and may be indicative of the level of pollution resulting from farm activities in the three locations. The high level of Cadmium could be attributed to the level of use of inorganic fertilizers in the farmers fields in the study area.

Keywords: Heavy metal; Agro-ecological zones; Agricultural soil; Soil depth; Uasin Gishu County.