Assessment of Heavy Metal Pollution in Water and Sediment of River Thiba, Kirinyaga County, Kenya

Abstract

Traceelementsfind their way into humans throughingestion, directabsorptionorinhalation. All tracemetals are toxic to animals and plants when present in excess amounts. The harmfuleffects of trace heavymetals in mammals may manifest asgrowth retardation, decrease in longevity, changes in reproductive cycles, chronic diseases and tumourformation. River Thibacatchment isMt. Kenya forestand thenflowsthrough rocks, soil, farmlands, residential areas and towncentres. Due to geological factors and human activities,traceheavy metals maybegettingin riverThibaand since the water is used for domestic purposes and irrigation, it was necessary to determine the heavy metal concentrationinthe river. Sedimentand watersamples were collected along river Thibaduring rainyand dry seasons. The samples were digested thenconcentrationsof eight heavy metals determined using ICP-MS. The mean amountsof Cd, Cr, Ni, Pb, Zn, As, Mn and Se in sedimentwere0.0908, 39.8969, 85.1085, 10.3918, 42.5555, 2.3679, 1678.3876and 5.4907mg/kg respectively during rainyseason and 0.0628, 42.6319, 396.4692, 3.2669,58.7585, 2.8139, 1766.4009 and 6.1059mg/kg respectively during dry season. The mean concentration of the same metals in water was 0.0002, 0.0916, 1.0066, 0.0434, BDL, 0.0025, 1.8484and0.0038ppm respectively during wet season and BDL,BDL, BDL,0.0068,BDL,0.00002, 0.0070 andBDL ppm respectively during dry season. The mean amount of Cr, Ni and Mn in sediment were found to be above WHO and US EPA permissible limitsduring both seasons.During rainy season, the mean concentration of Cr, Ni, Pband Mn in water were above WHO and KEBS/WASREB permissible limitsbut the concentrations of Cd, Zn, As and Se were below the limits. However, during dry season, all the eight heavy metal concentrations in water were below WHO, KEBS/WASREB permissible limits. As far as the eight heavy metals are concerned, water from river Thibamay not be potable during rainyseason but is potable during dry season. However, further investigations should be carried out to determine other water parameters.