Levels of fluoride ion and selected heavy metals and their impact on River Kimwarer environment in Kerio Valley- Kenya

Abstract

The levels of selected heavy metals in water, plant, soil and sediment samples collected around the Fluorspar Mining and Processing Plant in Kerio Valley were determined using AAS and EDXRFS. Digested soil 7 reference material (IAEA) was used as the standard for analysis of the soil and sediment samples. The results obtained from AAS were compared with those obtained using EDXRFS. The concentration of fluoride in the water, soil and sediment samples was determined using fluoride selective electrode. The mean concentrations in mg/Kg of the elements in the water samples ranged from 0.480 – 54.97 for Fe, 0.138 – 0.319 for Zn, 0.030 –1.280 for Mn, 0.026 – 0.117 for Cu, 0.015 – 0.275 for Pb, 0.000 – 0.102 for Cr and 0.600 – 40.08 for F-. The concentration of the heavy metals and fluoride in the soil and sediment samples though higher than those of the water samples followed a similar trend with the downstream and effluent stream samples having higher concentration than the upstream and lower downstream samples. There was a gradual decrease in concentration of these elements on descending the river lower downstream implying that the factory effluents were responsible for the increased levels of the selected metals and fluoride observed downstream. The roots of Eicchornia crassipes (water hyacinth) had the highest concentration of heavy metals and fluoride followed by the stems while the leaves had the lowest concentration of these elements. Adsorption studies of heavy metals using Eicchornia crassipes showed that the roots of the plant were the most effective in adsorbing the heavy metals and fluoride from artificially prepared solutions of the heavy metals with the mean % adsorption ranging from 75.71 – 85.44, the stems had moderate adsorption ranging from 40.39 – 63.45 while the leaves were the least effective with the mean % adsorption ranging from 23.33 – 37.56. Statistical analysis showed that there was significant difference between the upstream samples and downstream and effluent samples implying that the Fluorspar mining and processing plant was responsible for the increased concentration of heavy metals and fluoride downstream of river Kimwarer. Suitable control measures of reducing the concentration of the hazardous chemical effluents such as periodic excavation of the sedimentation ponds and phytoremediation were proposed.