Assessment Of Levels Of Selected Heavy Metals In Borehole Water In Ongata Rongai, Kajiado County, Kenya

Abstract

Heavy metal content in groundwater sources is of a growing concern as they are known to be persistent in nature and have been found to bioaccumulate in animals and plants. The heavy metals have been found to cause detrimental health effects to human beings and some of the effects include cancer, nervous system damages, respiratory diseases and even dermatological problems. There’r therefore, need to assess levels of heavy metals in water sources. This study was carried out to evaluate the quality of groundwater sampled from ten selected boreholes in Ongata Rongai town, Kajiado County. Selected heavy metals; zinc, lead, mercury, manganese, cadmium and chromium and associated physicochemical parameters; pH, dissolved oxygen, electrical conductivity, total dissolved solids, turbidity and total suspended solids were determined from the ten borehole sites together with human activities as sources of contaminants. Seasonal variation was considered as an aspect of pollution to the subsurface environment where there was no obvious observable environmental degradation. The heavy metals were determined by use of Flame Atomic Absorption Spectroscopy. Questionnaires were randomly issued to residents in the area to assess their knowledge of water quality and heavy metal knowledge. The physicochemical parameters determined were in the following ranges: pH 6.6±0.1 –8.6±0.1; dissolved oxygen 1.22±0.01- 4.83±0.01 (mgl-1), electric conductance 233±1.0-312±1.0 (mscm-1), total dissolved solids 630±1.3 - 980±1.0 (mgl-1); turbidity 0.04±0.01-0.7±0.01 Nephelomteric Turbidity Units (NTU); total suspended solids 0.9±0.1 - 2.6±0.01 (mgl-1), while for heavy metals; zinc Below Detectable Limits (BDL)- 0.73±0.01 (mgl-1); lead 0.21±0.01- 0.42±0.01 (mgl-1), mercury 0.0002±0.0001 - 0.0019±0.0001 (mgl-1); manganese 0.03±0.01- 0.26±0.01 (mgl-1). Cadmium and chromium had levels below limits of detection of 0.001 (mgl-1) and 0.005 (mgl-1) respectively. Statistical analysis of the data using a 1-Way Analysis of Variance (ANOVA) showed 95% confidence (p<0.05) interdependence of the distance from the boreholes and contaminant levels. The study concluded that lead and manganese levels were slightly higher in all water samples as compared to World Health Organization (WHO), Kenya Bureau of Standards (KEBS) and National Enrvironment Management Authority (NEMA). Cadmium and Chromium were below detectable limits irrespective of the season and proximity to septic tanks. There was no strong relationship between physical chemical parameters and proximity to septic tanks. The seasonal variation had no statistical significant effect on chemical parameters levels and they were within WHO, KEBS and NEMA. The responses from questionnaire showed that public awareness about water quality and vi effects of heavy metals should be done. It can also be concluded that the water is fit for consumption, however regular analysis are recommended and proper disposal management should be employed.