Trace Elements in Rainfall Collected Around Menengai Area Kenya

Abstract

Trace element concentrations were measured in precipitation collected from five sites in the Menengai geothermal area, central Kenyan rift region: two sites in the Centre of the caldera (Menengai Well 2, MW2 and Mlima Punda, MPA), two at the caldera edge, at Laydown Meteorological station (MTS) and Menengai Viewpoint (MVPT), and one in the northern part outside the caldera at Rigogo (RIGGO), between November 2011 and June 2012. The concentrations at these sites were compared with precipitation collected at a control station 30 km from study area at Egerton University Meteorological station. All samples were analyzed for trace metals (Al, Cd, Cr, Cu, Zn, Ni, Pb, Mn, B, As, Se and Mo). The majority of the rain samples collected had pH values higher than 6.2. The mean, median and mode pH was 6.58. High values of pH were attributed to the neutralization by natural alkaline local dusts which contain large fractions of calcite. Concentrations of measured trace elements species were within similar concentration range as those reported for other sites worldwide. Sources of the trace elements were also assessed based on enrichment factor method. The trace elements of anthropogenic origins (Hg, Zn, As, Se, Mo and Cd) were highly enriched with respect to crustal composition indicating the influence of anthropogenic input for these metals. The concentrations of trace metals that were determined in the rainwater samples were relatively low compared to World Health Organization drinking water quality guidelines hence potable for domestic use through rainwater harvesting.