Survey Of Levels Of Some Heavy Metals In Soil, Sugarcane And Some Sugarcane Products From Muhoroni And South Nyanza Sugar Companies Nucleus Estates, Kenya

ABSTRACT

Sugarcane is an important cash crop in Kenya. Due to its economic value, efforts are in progress to increase its production. The efforts include intense use of fertilizers, besides the use of high-yielding varieties. The intense use of fertilizers adds heavy metals to the sugarcane growing soils. The sugarcane plants can bioaccumulate heavy metals from soils to levels above safe limits. Metal levels in soil and factors such as soil pH and soil organic matter (SOM) influence levels of metals in food crops. Cultivation of sugarcane with intense use of fertilizers reduces soil pH and SOM content. Levels of cadmium (Cd), chromium (Cr), copper (Cu), lead (Pb) and zinc (Zn) accumulated in Muhoroni and South Nyanza (SONY) sugarcane estate soils and sugarcane, and soil pH values and SOM content have not been established. The objective of this survey research was to determine soil pH, SOM content and levels of some heavy metals in soil and sugarcane. Topsoil (0-30 cm) and sugarcane stems were randomly sampled from 90 sampling points in triplicate and collected in polyethene bags. Samples were digested in Aqua regia solution and analyzed for Cd, Cr, Cu, Pb and Zn content, and their corresponding contamination levels and bioaccumulation factors were evaluated. Levels of heavy metals in top-soils and in sugarcane were determined using Atomic Absorption Spectrophotometer. Data analysis was done using SPSS 20 and results compared with acceptable limits. The soils had medium SOM content and were strongly acidic. SOM contents were within range required by sugarcane while soil pH values were below optimum range. Levels of metals were low in soil samples and were within safe limits of European Union standards. Levels of Cd, Cu, Pb and Zn in stems were low and within WHO/FAO safe limits except for Cr. Levels of Cr, Cu and Zn in juice were low and within recommended maximum limit while the level of Cd in juice was 13 times higher than the maximum limit. Level of Pb in juice was also above recommended maximum limit. Bagasse contained low levels of metals which were within maximum permissible limit for adult livestock feeding. Bioaccumulation factors of the metals were below 1 showing that sugarcane did not bioconcentrate the metals. Sugarcane can be cultivated in these areas but measures be taken to reduce uptake of Cd and Pb. It is recommended that soil pH be increased to the range required by sugarcane.