Toxic Metals Pollution and Environmental Risk Assessment of Agricultural Soil in Uasin Gishu County, Kenya

Increased industrialization, typically mechanized farming, addition of agricultural inputs and urbanization are prime sources of metal toxicity in soil, sediment, and water in periurban areas. In Kenya, prolonged mono-cropping and use of agrochemicals trigger toxic (heavy) metals accumulation in environmental media. It is crucial to understand the link between anthropogenic activities and toxic metal concentration in soil in Kenya. Many farmers and residents that may be exposed to toxic metals are uninformed about the potential impacts of these metals on the ecosystem and human health. Soil samples were collected from Jema, Kaprobu, Moiben, Naiberi and Ziwa in Uasin Gishu County and analyzed for mineralogical and toxic metal compositions to assess the contamination and ecological risk indices. Algorithmic environmental risk assessment indices including Hakanson’s ecological index, Muller’s geo-accumulation index and potential ecological risk index were used to compute the likely health risk. Mean concentrations of toxic metals in soils from the study areas in an ascending order were: Mercury (Hg) < Cadmium (Cd) < Selenium (Se) < Arsenic (As) < Chromium (Cr) < Lead (Pb), that is ND, 0.10, 5.34, 27.75, 28.72, respectively. Lead concentration in studied soils was relatively high and its assessed contamination factor (Cf), Geo-Accumulation Index (Igeo), Contamination Degree (Cdeg), and Ecological Risk Index (Eri) showed varying degrees from moderate to very high Cf, moderate to strong Igeo, very high Cdeg and considerable potential Eri, respectively, in the study areas. The increase in Pb is attributable to anthropogenic farming activities in the studied areas. Key words: Environment risk assessment, geoaccumulation, Kenya, soil pollution, toxic metal, Uasin Gishu