Arsenic Contamination in Water from Selected Boreholes in Nairobi City County, Kenya

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. Its levels in drinking water must be regularly monitored and controlled. The objective of study was to determine the concentration of arsenic in water with reference to WHO limits from selected boreholes in Nairobi County, Kenya. Water was randomly sampled from a total of 63 boreholes in five zones (Central, Eastern, Northern, Western and Southern) during dry and wet season. The arsenic was analyzed by Hydride Generation Atomic Absorption Spectrometer (HG-AAS). The results showed that the arsenic content in borehole water during dry season ranged between 0.00455±0.0022 and 0.01007±0.006 and in the range of 0.002057±0.0008 - 0.00744±0.0051 mg/L during the wet season. There was significant difference (P˂0.05) in arsenic content in borehole water samples in Central zone compared to the other zones. During the dry season, arsenic content in water from ten boreholes (16%) and four boreholes (6%) during wet season was found to be above the WHO recommended limit of 0.01 mg/L. The calculated contamination factor for the borehole water ranged from slightly arsenic contaminated in Central zone to very slightly contaminated in the other zones during dry season. During the wet season, the borehole water in all the five zones were very slightly contaminated with arsenic. The pollution index showed that the boreholes in all the five zones during both wet and dry seasons were not polluted with arsenic. Steps should be taken to monitor and treat borehole water for domestic purposes in order to mitigate the effect on human health due to arsenic contamination.