Investigating geogenic lead contamination and its associated health effects in Kilifi area, Kenya

M.Sc. (Geology)Abstract: Lead (Pb) is ranked second in the most toxic substance list by Agency of Toxic Substances and Disease Registry (ATSDR). As a non-essential trace element, Pb presence in blood has no threshold safe limit with prolonged exposure affecting body systems especially brain development in children. In Kilifi area, sedimentary rocks of Triassic to Recent age host a base metal deposit of galena (PbS) that was extensively mined in the 1970s. Over 70% of the local population depends on natural land resources for their daily livelihood. To bridge the existing knowledge gap between ore deposit geology and associated chronic health conditions in the area, this study aimed at investigating the possible link between geogenic Pb and the prevalent chronic health issues affecting Kilifi residents. Soil, food crops and water samples were analyzed for Pb as well as other associated trace metals (Zn, Cu, Mn, Fe and Ba). Medical records collected from the County Health Office were reviewed for prevalent chronic diseases reported in ages below and above 5 years from 2011-2014. Neurodevelopmental disorders (NDD) prevalence in children aged 6-9 years old recorded between March 2015 and August 2016 were also obtained from KEMRI. Soil (n=55), plants (n=8) and water (n=15) samples were collected from random locations covered by Kilifi Demographic and Health Surveillance System (KDHSS) and beyond. Using X-Ray Fluorescence (XRF) technique, soil and plants samples were analyzed for Pb and associated metals. Water samples were analyzed for major cations and anions using inductively coupled plasma optical emission spectrometry (ICP-OES) and colorimetric discrete techniques. All the data was statistically and geospatially processed. Metals concentration in soil is found to be in the ranges of Pb=0.02-370.13; Zn=5.65-389.59; Cu=2.37-30.45; Mn=559.58-3962.81; Ba=3436.8-153675 and Fe=287.06-52472.9 mg/kg respectively. Out of the 55 soil samples, 20% of them had Pb levels exceeding WHO limit of 0.1-20 mg/kg for normal ranges of Pb in soil. In cassava tubers (Manihot esculenta) metals concentration is found to be in the ranges of Pb=0.39-0.49; Zn=17.10-59.54; Cu=2.39-5.74; Mn=132-315.25 and Fe=261.72-789.18 mg/kg respectively. In maize (Zea mays) the metals concentration is Pb=0.42; Zn=35.43; Cu=4.51; Mn=367.63 and Fe=751.53 mg/kg respectively. Metals concentration in cowpea leaves (Vigna unguiculata) are Pb=0.45; Zn=39.72; Cu=5.74; Mn=190.76 and Fe=204.84 mg/kg respectively while in baobab fruit (Adansonia digitata) the metals concentration is Pb=0.39; Zn=23.74; Cu=3.80; Mn=290.03 and Fe=634.17 mg/kg respectively. 100% plant samples (n=8) show Pb quantities above WHO limits of 0.3, 0.2 and 0.1 mg/kg for leafy vegetables, cereals/grains and..