Determination of Selected Heavy Metals in Tobacco Tree Shrubs Growing around Dandora Dumpsite, Nairobi, Kenya

Abstract

Environmental pollution by heavy metals is presently a serious threat to public health. Despite the toxic contaminants contained in municipal waste, most of the dumpsites remain unregulated and uncontrolled. The objective of this study was to determine the levels of Pb, Cr and Cd in the leaves of tobacco tree plants growing around the dumpsite so as to assess their impact on the environment. The pseudo-total concentration of the metals in the soil was done so as to calculate the transfer factors.pH and total organic carbon (TOC) of the soil was also determined. Soil and plant samples were collected thrice from thirty two sampling sites along the off-loading path from the centre of Dandora dumpsite up to a distance of 700 m away from the centre at depth of 0-30cm (top soil).  Metal analysis was done using flame atomic absorption spectroscopy (FAAS). Pb levels ranged from 7.58±0.34 to 16.57±0.79 µg/g in the washed leaves and 9.22±0.36 to 19.27±0.40 µg/g in the unwashed leaves. Cr levels ranged from 5.11±0.40 to 14.4±0.91 µg/g in the washed leaves and 5.01±0.45 to 15.50±0.40 µg/g in the unwashed leaves. While Cd levels ranged from 0.24±0.01 to 3.62 ±0.17 µg/g in the washed leaves and 0.37±0.02 to 3.68±0.25 µg/g in the unwashed leaves. All these levels were above World Health Organization recommended limits in plants of Pb (0.3 µg/g), Cr (3 µg/g) and Cd (0.2 µg/g). Pearson correlation of the levels in the plants with their concentrations in the soils gave significantly positive values. This suggest that high metal concentration in the soil leads to increased mobility and hence bioavailability. Results obtained therefore suggest that Dandora dumpsite is highly polluted and people should be discouraged from using waste from the dumpsite as manure.