ASSESSMENT OF LEVELS OF SELECTED HEAVY METALS AND COLIFORM BACTERIA IN SOIL AND VEGETABLES GROWN AT ELDORET MUNICIPAL DUMPSITE

Abstract

Agricultural practices are on the rise in urban areas of developing countries; Kenya included due to the high rate of urbanization which comes with associated challenges such as increased demand for food and employment. Urban farming is viewed as an important practice since it is a source of income and food. However, limited land spaces in urban areas and the rising cost of artificial fertilizers have been a major challenge to urban farming. Consequently, farmers especially the low income earners are forced to use free land to grow food crops and use raw sewage sludge to enhance fertility of the food crops. In Eldoret, the old municipal dumpsite has become an ideal site for growing vegetables. Sewage sludge is applied to the vegetables without regard to risks caused by toxic heavy metals and pathogenic contamination. Heavy metals are known to accumulate along the food chain. Prolonged consumption of unsafe concentrations of heavy metals may lead to their accumulation in the human body causing disruption of numerous biochemical processes. Pathogenic organisms on the other hand are known to be precursors to diseases like dysentery, typhoid, tetanus and cholera among others. This research was conducted to determine levels of lead, cadmium, copper, zinc, iron, nickel, total coliform, faecal coliform and E. coli contamination in soil, kales (Brassica oleracea), spinach (Spinacea oleracea) and bulb onions (Allium cepa) grown at the old Eldoret municipal dumpsite and irrigated using raw sewage sludge. Levels of coliform bacteria were assessed using multiple tube fermentation technique while heavy metal contaminants were analysed using atomic absorption spectroscopy (AAS). A total of 60 samples were used in two experimental runs carried out between July 2013 and January 2014 to cater for both dry and wet seasons. All data were analysed using SPSS version 20.0 and significance was considered at p < 0.05. Comparison of mean concentration of heavy metals in soil and vegetables and the mean concentration of heavy metals in soil and vegetables during dry and wet seasons was done using paired t-test. The results obtained from municipal dumpsite soil indicated the following mean concentrations: Pb, 1.630 mg/kg, Cd, 0.070 mg/kg, Cu, 0.380 mg/kg, Zn, 2.310 mg/kg, Fe, 101.530 mg/kg and Ni, 10.370 mg/kg. In kales mean concentration of heavy metals were as follows: Pb, 1.356 mg/kg; Cd, 0.110 mg/kg; Cu, 0.095 mg/kg; Fe, 42.070 mg/kg; Zn, 0.875 mg/kg and Ni, 9.240 mg/kg. In spinach the following concentrations were obtained: Pb, 1.088 mg/kg; Cd, 0.090 mg/kg; Cu, 0.103 mg/kg; Zn, 0.800 mg/kg; Fe, 22.110 mg/kg and Ni, 9.190 mg/kg. In onions mean concentration of heavy metals were as follows: Pb, 0.404 mg/kg; Cd, 0.345 mg/kg; Cu, 0.109 mg/kg; Zn, 2.650 mg/kg and Fe, 2.650 mg/kg. Levels of total coliform and feacal coliform in the soil were 3,893 and 3,068 MPN/100 ml respectively while in onions the levels were 10,576 and 5,861 MPN/100 ml respectively. Levels of all the heavy metals were within the acceptable range of WHO/FAO in soil. In vegetables, Pb and Cd were above the acceptable limit while Cu, Zn, Fe and Ni were within the acceptable standard. Levels of faecal coliform in soil and onions were above recommended standard. It was therefore concluded that the vegetables grown in the old Eldoret municipal dumpsite and irrigated using raw sewage sludge are not good for human consumption since they have high levels of Pb, Cd and faecal coliform which are likely to pose health complications to consumers.