Determination of Arsenic Concentration and Contamination Factor in Water from Selected Boreholes in Nairobi City County, Kenya
Kiplangat, S. Alice
MetadataShow full item record
Arsenic is a metalloid, which may be found in surface water, ground water, plants and rocks. In high concentrations, its compounds are considered to be genotoxic and carcinogenic. Arsenic enriched minerals and bearing rocks have been the chief source of arsenic (As) in the ground water. Anthropogenic activities such as improper waste disposal and landfill, excessive use of fertilizers, pesticides and herbicides has also contaminated the groundwater quality to a larger extent. In Nairobi City County, there has been increased number of drilled water boreholes “in thousands,” to meet the demand of the scarcity of water resources. However, there is a high possibility of having some of these boreholes in contaminated sites. Thus there is increased concern on the safety and quality of these borehole water due to possible contamination with toxic heavy metals such as mercury, cadmium and in particular arsenic. The objective of study was to determine the concentration and contamination factor of arsenic in water from selected boreholes in Nairobi City, County. Water was randomly sampled from a total of sixty three (n-63) boreholes in five (5) zones (Central, Eastern, Northern, Western and Southern) during the dry and wet seasons. The arsenic was analyzed by Hydride Generation Atomic Absorption Spectrometer (HG-AAS). The results showed that the arsenic content in borehole water during the dry and wet seasons ranged from 0.00455 0.0022 - 0.01007 0.0060 and 0.002057±0.0008 0.00744±0.0051 mg/L respectively . There was a significant difference (P˂0.05) in arsenic content in borehole water samples in Central zone compared to the other zones. The a rsenic content in water from ten bor eholes (16 %%) during the dry season and four boreholes (6%) during the wet season was found to be above the WHO recomm ended and NEMA regulatory limit of 0.01 mg/L. During the dry season, the calculated contamination factor (CF) for the borehole water ranged from moderately contaminated to very severely contaminated (CF 0.26 – 1.0). On the other hand during the wet season, it ranged from slightly contaminated to severely contaminated (CF 0.10 - 0.74). Therefore, the borehole water for domestic purposes requires monitoring in order to mitigate the effect on human health.