Determination of levels of selected heavy metals in soil and vegetables grown at the Market Dumpsite in Eldoret, Kenya.

Abstract

Dumpsite in urban centres are often used for agricultural purposes due to their nutrient- rich soils without regard to the risks of toxic heavy metal. In a similar quest Eldoret market dumpsite is becoming an ideal site for growing vegetables. Consequently, heavy metals accumulate in the vegetables then pass to human beings through consumption causing numerous adverse effects. This research was conducted to determine levels of lead (Pb), cadmium (Cd), copper (Cu), zinc (Zn), iron (Fe) and nickel (Ni) in the soil, then kales (Brassica oleracea) and spinach (Spinacea oleracea) grown in Eldoret market dumpsite. Sampling was done between the month of November 2014 to August 2015 to cover for the dry and wet seasons. The collected vegetable samples were oven-dried at 60 o C, ground and digested using mixture of Li 2 SO 4 , Se, H 2 SO 4 and H 2 O 2 while soil samples were oven-dried at 80 o C, crushed and digested with same mixture as the vegetable samples. The levels of heavy metal in the samples were analyzed using Atomic Absorption Spectroscopy (AA). Calibration graphs were generated using standard solution of concentration ranging from 5 ppm to 20 ppm that gave values of R 2 ranging from 0.9962 to 0.9995. All data were analyzed using SPSS and significance considered at p<0.05. Significance of variation in heavy metals concentrations for soil and in the vegetables during dry and wet season was statistically analyzed using unpaired t-test. The results showed that the soils had the following mean concentrations of heavy metals for the dry (D) and wet (W) seasons: Pb 1.74 mg/Kg (D) and 1.53 (W) mg/Kg, Cd 1.07 mg/Kg for both dry and wet seasons, Cu 51.75 mg/Kg (D) and 50.33 mg/Kg (W), Zn 72.68 mg/Kg (D) and 61.94 mg/Kg (W), Fe 552.51mg/Kg (D) and 554.56 mg/Kg (W) and Ni 52.56 mg/Kg (D) and 54.55 mg/Kg (W). In kales, mean concentration of heavy metals for both seasons were: Pb 1.435 mg/Kg; Cd 0.11 mg/Kg; Cu 41.24 mg/Kg; Fe 454.44 mg/ Kg; Zn 33.67 mg/Kg and Ni 40.08 mg/Kg. In spinach the concentrations obtained for dry and wet seasons were: Pb 0.936 mg/Kg; Cd 0.89 mg/Kg; Cu 42.17 mg/Kg; Fe 441.05 mg/ Kg; Zn 33.80 mg/Kg and Ni 38.19 mg/Kg respectively. The Levels of the heavy metals in vegetables were above the WHO/FAO acceptable limits except for Zn and Ni. The t-test results gave values of p <0.05 implying that there was significant differences between the concentration of the heavy metals in the vegetables and in the soils. Based on the findings, it was therefore concluded that the vegetables grown in the Eldoret market dumpsite are not safe for human consumption due to the high levels of lead, cadmium, iron and copper which are likely to pose health complications to consumers. In order to safeguard people from these toxic vegetables, farming activities in the Eldoret market dumpsite should be prohibited.