Characterization of dispersion of heavy metals through dust a case study of Lake Nakuru Basin

Abstract

In many tropical countries, there has been rapid industrialization without corresponding legislation and control of environmental effects. The particulate and gaseous pollutants emitted into the atmosphere cause a serious threat due to their quick and uncontrolled spread. The knowledge of the extent of environmental pollution in Kenya is limited. Lake Nakuru which is the core of the Lake Nakuru Basin (LNB) is a closed drainage system which means that all the effluents’ deposited into it including heavy metals accumulates in the lake. This research was carried in 2009 when LNB had suffered long periods of no precipitation and atmospheric dry deposition was occurring. The high temperatures around the basin causes high evaporation in the lake and the residue left is relatively light consisting mainly of carbonate and bicarbonate. This coupled with the high wind speeds, allows re-suspension of soil particles. This study aimed at determining the metal types and their concentrations in the dust dispersed by wind within the basin, and identifying whether the lake could be a potential source of heavy metals in atmospherically deposited dust. Flame atomic absorption spectrometry (FAAS) was used to analyze the concentration of Pd, Zn, Ni, Fe and Cr in 33 samples of suspended particulate matter which were collected from rooftops made of galvanized iron around the LNB. Statistical analyses were done using SPSS version ll.5 and EXCEL spreadsheets. The results of the analyses showed that LNB had the concentrations of the metals varying in the order Fe > Zn > Cr > Pb with mean values of l6.l t 2.5 ppm, 5.5 t 5.7 ppm, 0.3 i 5.7 ppm and 0.2 i 0.1 ppm, respectively. The mean values for these metals in the control locality outside the LNB were 10.7 1 1.3 ppm and 0.3 1- 0.1 ppm for Fe and Zn, respectively. Nickel and the other metals were not detected. All these values were well below the WHO recommended limits of aerial particulate matter in the atmosphere but could, however, be an indicator of the pollution potential of the LNB by increased human and industrial activities. Furthermore, the only values for heavy metals in the carbonate and bicarbonate residues observed in samples collected at the lake were 17.0 i 4.9 ppm and 0.4 1- 0.1 ppm for Fe and Zn respectively and were actually not significantly different from those found in the rooftop sites within the LNB. Therefore, the lake may be ruled out as the main source of heavy metals present in the suspended particulate matter of the LNB since there was no significant decrease of the levels of heavy metals studied with progressive increase in distance from the lake.